Main Radiation Effects in Materials

Radiation Effects in Materials

Categories: Technique\\Materials
Year: 2016
Publisher: ExLi4EvA
Language: english
Pages: 453
ISBN 13: 978-953-51-2418-4
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Radiation Effects in Materials
Edited by Waldemar A. Monteiro

Radiation Effects in Materials
Edited by Waldemar A. Monteiro

Published by ExLi4EvA
Copyright © 2016
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Contents

Preface

Chapter 1 Effects of Electron Irradiation Upon Absorptive and
Fluorescent Properties of Some Doped Optical Fibers
by Alexander V. Kir’yanov
Chapter 2 Radiation Effects in Optical Materials and Photonic
Devices
by Dan Sporea and Adelina Sporea
Chapter 3 The Impact of Successive Gamma and Neutron
Irradiation on Characteristics of PIN Photodiodes and Phototransistors
by Dejan Nikolić and Aleksandra Vasić-Milovanović
Chapter 4 Electron Beam Irradiation Effects on Dielectric
Parameters of SiR–EPDM Blends
by R. Deepalaxmi, V. Rajini and C. Vaithilingam
Chapter 5 Radiation and Environmental Biophysics: From Single
Cells to Small Animals
by Yanping Xu
Chapter 6 Radioactivity in Food: Experiences of the Food Control
Authority of Basel-City since the Chernobyl Accident
by Markus Zehringer
Chapter 7 Radiation Influence on Edible Materials
by Nelida Lucia del Mastro
Chapter 8 Transient Anions in Radiobiology and Radiotherapy:
From Gaseous Biomolecules to Condensed Organic and Biomolecular
Solids
by Elahe Alizadeh, Sylwia Ptasińska and Léon Sanche

VI

Contents

Chapter 9 Elimination of Potential Pathogenic Microorganisms in
Sewage Sludge Using Electron Beam Irradiation
by Jean Engohang-Ndong and Roberto M. Uribe
Chapter 10 Radiation Effects in Polyamides
by Mária Porubská
Chapter 11 Ion-Irradiation-Induced Carbon Nanostructures in
Optoelectronic Polymer Materials
by Taras S. Kavetskyy and Andrey L. Stepanov
Chapter 12 Radiation Effects in Textile Materials
by Sheila Shahidi and Jakub Wiener
Chapter 13 Irradiation Pretreatment of Tropical Biomass and
Biofiber for Biofuel Production
by Mohd Asyraf Kassim, H.P.S Abdul Khalil, Noor Aziah Serri, Mohamad
Haafiz Mohamad Kassim, Muhammad Izzuddin Syakir, N.A. Sri Aprila
and Rudi Dungani
Chapter 14 Ion Bombardment-Induced Surface Effects in
Materials
by Farid F. Umarov and Abdiravuf A. Dzhurakhalov
Chapter 15 Neutron Irradiation Effects in 5xxx and 6xxx Series
Aluminum Alloys: A Literature Review
by Murthy Kolluri
Chapter 16 A Parallel between Laser Irradiation and Relativistic
Electrons Irradiation of Solids
by Mihai Oane, Rareş Victor Medianu and Anca Bucă
Chapter 17 Nanostructuring of Material Surfaces by Laser
Ablation
by Cinthya Toro Salazar, María Laura Azcárate and Carlos Alberto
Rinaldi

Preface

The study of radiation effects has developed as a major field of
materials science from the beginning, approximately 70 years ago. Its
rapid development has been driven by two strong influences. The
properties of the crystal defects and the materials containing them may
then be studied.
The types of radiation that can alter structural materials consist of
neutrons, ions, electrons, gamma rays or other electromagnetic waves
with different wavelengths. All of these forms of radiation have the
capability to displace atoms/molecules from their lattice sites, which is
the fundamental process that drives the changes in all materials. The
effect of irradiation on materials is fixed in the initial event in which an
energetic projectile strikes a target.
The book is distributed in four sections: Ionic Materials; Biomaterials;
Polymeric Materials and Metallic Materials.

Chapter 1

Effects of Electron Irradiation Upon Absorptive and
Fluorescent Properties of Some Doped Optical Fibers
Alexander V. Kir’yanov
Additional information is available at the end of the chapter
http://dx.doi.org/10.5772/63939

Abstract
A review of the recent studies of the effect of irradiating silica-based fibers doped with
rare earths and metals by a beam of high-energy (β) electrons is presented. Of the
review’s main scope are the attenuation spectra’ transformations occurring in optical
fiber of such types under electron irradiation, allowing, from one side, to recover some
general essence of the phenomena involved and, from the other side, to draw the
features that would make such fibers useful for applications, for example, in dosime‐
try and space technologies. Among the fibers of the current review’s choice, exempli‐
fying the effect of electron irradiation most brightly, are ytterbium (Yb) and cerium (Ce)
(the rare earths’ representatives) and bismuth (Bi) (the post-transitional metals
representative) doped fibers, where a diversity of the electron-irradiation-related effects
is encouraged.
Keywords: electron irradiation, ytterbium-, cerium- and bismuth-doped silica fibers,
photodarkening, optical bleaching

1. Introduction
In this chapter, a few examples are demonstrated of the impact of high-energy (β) electrons
irradiation on the absorptive and fluorescence properties of silica-based optical fibers doped
with rare earths and metals. The results presented hereafter seem to be useful for understand‐
ing the processes standing behind the highlighted phenomena and for possible applications of
the fibers, say, in dosimetry and space technology.
In each case, we used for irradiating fiber samples a controllable linear accelerator of the
LU type that emits β-electrons with a narrow-band energy spectrum (~6 MeV) in a shortpulse (~5 μs) mode. The samples with lengths of around 1–2 m were placed into the

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Radiation Effects in Materials

accelerator’s chamber for various time intervals, which provided growing irradiation doses.
The irradiated fibers were then left for 2 weeks prior to the main-course spectral measure‐
ments to avoid the role of short-living components in the decay of induced absorption (IA).
The measurements were done during a limited time (viz., the following 2…3 weeks) for
diminishing the effect of spontaneous IA recovering. Note that ionization, that is, the
production of β-induced carriers by an electron beam (i.e., of secondary free holes and
electrons), is the main cause of the spectral transformations in the fibers. This happens
because high-energy primary β-electrons are virtually nondissipating at the propagation
through a fiber sample; on the other hand, certain contribution in ionization of the fibers’
core-glasses arising from γ-quanta born at inelastic scattering of the high-energy electrons
cannot be disregarded.
We demonstrate below first a study of the resistance of a couple of cerium (Ce)-doped
alumino-phospho-silicate fibers (one of them being codoped with gold (Au)), to β-electrons.
The experimental data reveal a severe effect of β-irradiation upon the fibers’ absorptive
properties, given by noticeable susceptibility of Ce ions being in Ce3+/Ce4+ states to the
treatment, arising as growth followed by saturation of IA. We also report the essentials of
posterior bleaching of β-darkened fibers, also in terms of attenuation spectra’ transforma‐
tions, at exposing them to low-power green (a He-Ne laser) and ultra violet (UV, a mercury
lamp) light. It is shown that both phenomena are less expressed in Ce fiber codoped with Au
than in Au-free one and that the spectral changes in the former are more regular versus dose
and bleaching time.
Then, we provide a comparative experimental analysis of IA, induced by β-electrons, for a
series of ytterbium (Yb)-doped alumino-germano-silicate fibers with different concentrations
of Yb3+ ions and compare this effect with the photodarkening (PD) phenomenon in the same
fibers, arising at resonant (into 977 nm absorption peak of Yb3+ ions) optical pumping. The
experimental data obtained reveals that, in these two circumstances, substantial and complex
but different in appearance changes affecting the resonant absorption band of Yb3+ ions and
the off-resonance background loss are produced in the fibers.
Finally, we report a study of attenuation spectra’ transformations in a set of bismuth (Bi)-doped
silica fibers with various contents of emission-active Bi centers, which occur as the result of
β-irradiation. Among the data obtained, notice a substantial decrease of concentration of Bi
centers, associated with the presence of Germanium (Ge) in core-glass, with increasing
irradiation dose (the “bleaching” effect), while, on the contrary, an opposite trend, that is, dosedependent growth of resonant-absorption ascribed to Bi active centers, associated with the
presence in core-glass of Aluminium (Al). These results are worth noticing for understanding
the nature of Bi-related centers in silica fibers, yet uncovered.

2. The effects of electron irradiation and posterior optical bleaching in
Ce-doped and Ce/Au-codoped alumino-phospho-silicate fibers
Development of suitable host glasses and fibers for dosimetry, which are based on formation
of radiation-induced defects leading to glass coloration [1–6] or filling pre-existing traps,

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers
http://dx.doi.org/10.5772/63939

measured by means of thermally or optically stimulated fluorescence [7], became a hot task.
Dosimetry systems can be used in high radiation fields, for example, in proximity to nuclear
reactors, hazardous places, and in open space. Fiber-based dosimeters are being intensively
investigated and recently a few systems have been proposed, based on versatile physical effects
in radiation-sensitive silica fibers [8].
Cerium (Ce)-doped silica glass has interesting fluorescent properties [9], which makes it
promising for utilizing as a scintillator for detecting X- and γ-rays, or neutrons [10, 11]. On the
other hand, silica glass is known to suffer from the presence of point defects and OH groups,
responsible for nonradiative recombination channels competing fluorescence. In turn, Au,
when combined with cerium oxide (CeO2) is known to be a promising catalyst for the reaction
CO + H2O→H2 + CO2 [12, 13], giving a way to remove carbon-related impurities along with
OH groups from silica matrix during synthesis. Thus, Ce/Au codoped glass is expected to
enhance efficiency of energy transfer from the host matrix to emissive centers. The other
motivation for Au codoping is to increase radiation resistance of Ce-doped fiber, as argued in
more details below. The refereed properties of alumino-phospho-silicate glass doped with Ce
and Ce/Au are also a concern of optical fibers made on its base.
Below, the results of experiments on irradiating Ce-doped alumino-phospho-silicate fibers by
energetic β-electrons are highlighted, resulting in the fibers darkening. It is furthermore shown
that the irradiated fibers are sensitive to weak light of a He-Ne laser (543 nm) and UV mercury
lamp, both leading to partial recovery of their initial properties. The whole of experimental
data evidences notable susceptibility of Ce-doped fibers to both kinds of treatment. As well,
it is demonstrated that the spectral transformations occurring in Ce fiber codoped with Au are
less expressed but more regular upon β-irradiation dose and exposure time when bleaching
than those in Au-free fiber. A brief discussion in attempt of a reasonable explanation of the
experimental laws completes the study, with the key point being a discussion about the species
involved in the processes, which are associated with Ce.
The reported results may have value for using Ce-doped silica fibers for dosimetry in harmful
environments [8, 14–20] and inscribing Bragg gratings [21–25]. As well, these results seem to
be impactful, given by renewed interest to Ce codoping as a tool for diminishing PD in Ybdoped fibers (we inspect the last effect in detail in Paragraph 3).
2.1. Fiber samples and experimental arrangement
The sourcing Ce-doped and Ce/Au-codoped fiber preforms based on alumino-phosphosilicate glass have been made by means of modified chemical vapor deposition (MCVD)
process employed in conjunction with solution doping (SD) technique; the final fibers have
been drawn from the preforms using a drawing tower. Core diameters/numerical apertures
of the two fibers were measured to be ~25 μm/0.15…0.16, respectively.
Estimated from EDX, average doping levels were found to be 5.0 wt.% Al2O3, 0.15 wt.% P2O5,
0.3 wt.% CeO2 (in the Ce-doped fiber) and 5.1 wt.% Al2O3, 0.15 wt.% P2O5, 0.27 wt.% CeO2, and
0.2 wt.% Au2O3 (in the Ce/Au-codoped fiber). Both fibers had multimode wave-guiding, which
make them useful for sensor applications. A sample of standard multimode Al-doped (~6 wt.

5

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Radiation Effects in Materials

% Al2O3) fiber was used in experiments for comparison. The β-irradiation dosage below
corresponds to 1 × 1012 (“dose 1”), 5 × 1012 (“dose 2”), 1 × 1013 (“dose 3”), 5 × 1013 (“dose 4”), 1
× 1014 (“dose 5”), and 2.5 × 1015 (“dose 6”) cm–2.
Optical transmission spectra of fiber samples were measured (employing the cutback method),
using a white light source and optical spectrum analyzer (OSA), turned to a 5 nm resolution.
Such spectra were recorded before and after each stage of β-irradiation and at posterior
exposure to light of a He-Ne laser (543 nm) or UV lamp (λ <450 nm). The attenuation spectra
presented below were obtained after recalculating the measured transmissions into loss
[dB/m]. In some of the figures below the difference spectra in terms of IA are provided, which
were obtained after subtraction of the attenuation spectra of pristine samples from the ones
taken after a certain dose of β-irradiation; this allows one straightforward view on the “net”
spectral loss changes in the darkened fibers. The transmission dynamics at optical bleaching
of β-darkened fibers by 543 nm light was inspected applying “frontal” detecting geometry
where a beam of the He-Ne laser was coupled into a fiber sample, while the transmitted light
was detected using a Si photodetector; this permitted detection of the changes in transmission
in situ. The results of the measurements are given below in terms of absorption difference (AD)
at bleaching with respect to the initial (β-darkened) state of the fiber. The experiments on
optical bleaching of β-irradiated fibers by UV light were as well proceeding in situ, where
transmission change at long-term exposure to UV light was analyzed. All experiments were
made at room temperature.
2.2. Experimental
2.2.1. IA as a result of β-irradiation
In Figure 1, we demonstrate (a) attenuation spectra of the Ce-doped (black solid curve 1) and
Ce/Au-codoped (grey dashed curve 2) fibers before irradiation, that is, in their “pristine” state,
and (b and c) the fibers’ cross-sections, obtained at white light illumination. Long (meters)

Figure 1. (a) Attenuation spectra of pristine Ce-doped (1), Ce/Au-codoped (2), and Al-doped Ce-free (3) fibers in a VISto-near-IR spectral range and micro-photographs of pristine Ce-doped (b) and Ce/Au-codoped (c) fibers. (Reproduced
with permission from Kir’yanov et al. [75]. Copyright© 2014, Optical Society of America).

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers
http://dx.doi.org/10.5772/63939

fibers were used in the measurements applying the cutback method, whereas short (10
centimeters) pieces of fibers—at microscopy. For comparison, spectral loss of “standard” Aldoped Ce-free fiber is presented in Figure 1(a)—see red dash-dotted curve 3.
We reveal from (a) that, in both Ce-doped and Ce/Au-codoped fibers, dramatic growth of
absorption occurs toward UV, below ~550 nm, which is known to be a shoulder of the strong
absorption bands adherent to Ce3+/Ce4+ ions (mostly located in UV [23, 24]), and that no such
feature is observed in the reference Ce-free fiber. Also notice steep loss rise in Ce-doped and
Ce/Au-codoped fibers toward IR and a small peak at ~520 nm (asterisked), the features not
observed in case of the Ce-free fiber.
Figure 2 shows the trends occurring in the fibers’ attenuation spectra as the result of βirradiation at moderate dose 4. Note that in this case, the measurements were proceeding with
shorter fiber samples (~a few cm) in virtue of strong IA, established after β-irradiation.

Figure 2. (a) Attenuation spectra of Ce-doped (1), Ce/Au-codoped (2), and Al-doped cerium-free (3) fibers, all meas‐
ured after β-irradiation with dose 4 (5 × 1013 cm–2) and micro-photographs of Ce-doped (b) and Ce/Au-codoped (c) fi‐
bers recorded after irradiation with this dose. (Reproduced with permission from Kir’yanov et al. [75], Copyright©
2014, Optical Society of America).

It is seen that IA in the Ce-free fiber is ~two times bigger than in the Ce-doped and Ce/Aucodoped ones. The other fact is that IA maxima are located near 400 and 500 nm in these two
fibers, whereas the ones in the Ce-free one—at ~400 and ~600 nm, that is, in the range most
probably attributing to well-known nonbridging oxygen-holes (NBOHCs) [26] (while the
presence of other defect states in it—such as Si-/Al-defect centers cannot be excluded).
Furthermore, it is seen from photos (b) and (c) that, in the Ce-doped and Ce/Au-codoped fibers,
the core and adjacent core-cladding areas suffer darkening after β-irradiation, in the former,
the effect being more pronounced.
Figure 3 demonstrates that IA in the Ce-doped (a) and Ce/Au-codoped (b) fibers increases
monotonously with dose; this trend is noticeable for the 400–700 nm range, while for bigger
wavelengths it fades. The other detail seen is that for moderate doses (1–4), IA is stronger in
the Ce-doped fiber.

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Radiation Effects in Materials

Figure 3. Main frames: IA spectra of Ce-doped (a) and Ce/Au-codoped (b) fibers; curves 1–6 correspond to doses of
irradiation (in both figures) being: 1 × 1012 (1), 5 × 1012 (2), 1 × 1013 (3), 5 × 1013 (4), 1 × 1014 (5), and 2.5 × 1015 (6) cm–2.
Insets: average IA-losses measured within the 1300–1550 nm range vs. irradiation dose. (Reproduced with permission
from Kir’yanov et al. [75]. Copyright© 2014, Optical Society of America).

The two-peaks structure of the IA spectra is apparent at higher irradiation doses for both fibers,
with the first peak (bigger in magnitude) locating at ~415 ± 10 nm and the second one (lower
in magnitude)—at ~520 ± 10 nm (compared to the ~520 nm peak asterisked in the attenuation
spectra of pristine fibers in Figure 1(a)). To evaluate IA strength in the fibers in function of βirradiation dose, let us compare the IA spectra with the attenuation spectra of the same fibers
being in pristine state (refer to Figure 1). It is known that attenuation growth toward UV is
common for Ce-doped glass, as stemming from the transitions inherent to Ce3+/Ce4+ ions.
(Unfortunately, IA arising in the UV-region, below 400 nm, was undetectable using our
experimental equipment.) Regarding IA in the near-IR, note that the spectral transformations
in this region are more complex (see insets to Figure 3) whose nature is unclear at the moment.

Figure 4. Main frames: dose dependences of IA for Ce-doped (a) and Ce/Au-codoped (b) fibers; blue and red symbols
and lines show IA magnitudes of bands 1 and 2, obtained after deconvolution of the spectra shown in Figure 3. Insets:
examples of deconvolution of the data obtained for the fibers, irradiated with dose 5 (spectra are plotted in eV-do‐
main). (Reproduced with permission from Kir’yanov et al. [75]. Copyright© 2014, Optical Society of America).

Deconvolution of IA spectra (Figure 3) allows a closer view on their two-band structure (see
insets in Figure 4(a) and (b)). Spectral locations of the bands (1 and 2) were found to be almost
independent of irradiation dose, for both fibers: they are centered at ~3.0 and ~2.4 (±0.1) eV
and are measured in half-widths at a 3 dB level by ~0.3 and ~0.5 (±0.05) eV, respectively. In
main frames of Figure 4, IA—in terms of these two peaks’ magnitudes—is plotted versus
irradiation dose; these dependences are shown, respectively, by blue (band 1) and red (band

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers
http://dx.doi.org/10.5772/63939

2) symbols. Fitting them within domain of smaller doses (up to ~2 × 1013 cm–2), linear growth
of IA in both bands versus dose is revealed (see the blue and red lines in the figure).
The slopes’ values estimated as the result of fitting were found to be ~1.7 (~1.2 dB/m/cm2) (Cedoped fiber) and ~1.3 (~0.9 dB/m/cm2) (Ce/Au-codoped fiber), correspondingly, for bands 2
and 1. It deserves mentioning that these ratios, on one hand, are almost equal for both fibers
(~1.5) and, on the other hand, the slopes’ ratios, when compared for bands 1 and 2, are vastly
equal as well (~1.3). Furthermore, at bigger irradiation doses IA, in both bands and for either
fiber, steadily approaches the “plateaus”, marked by black dotted lines in the figures. It is
interesting that IA in maxima of bands 1 and 2 at the plateaus (i.e. at doses exceeding 2 ×
1014 cm-2) has virtually the same magnitude, for both fibers.
2.2.2. Bleaching of IA as a result of posterior exposure to 543 nm/UV light
Hereafter, the featuring data on optical bleaching of β-irradiated Ce-doped and Ce/Aucodoped fibers by a low-power He-Ne 543 nm laser and UV mercury lamp are reported.

Figure 5. Dynamics of attenuation decay in terms of AD in Ce-doped (a) and Ce/Au-codoped (b) fibers under the ac‐
tion of 543 nm light (~0.5 mW); bleaching (negative AD) was realized after β-irradiation with doses 2 (curves 1), 4
(curves 2), and 6 (curves 3), for which AD is taken to be zero. (c) Micro-photographs of darkened (dose 5 of β-irradia‐
tion) Ce-doped fiber prior to (top) and after bleaching during 7.5 h (bottom). (d) Examples of the initial 543 nm bleach‐
ing stage, zooming the dependences shown by curves 2 in (a) and (b), respectively. (Reproduced with permission from
Kir’yanov et al. [75]. Copyright© 2014, Optical Society of America).

Keeping in mind that, IA, a signature of color centers or defects in glass matrix produced at
different kinds of irradiation, can be “bleached” by light (see e.g. [59–61]), we found reasonable
to check whether such treatment has effect in our case.
First, we inspected the effect of weak 543 nm light delivered from a 1.5 mW He-Ne laser. In
the experiments, power launched into both fibers was fixed (~0.5 mW; coupling efficiency

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Radiation Effects in Materials

~30%). In this case, very short pieces (1…2 cm) of β-irradiated fibers were handled, given big
IA, measured by hundreds of dB/m (refer to Figures 3 and 4), being established at β-darkening.
The results are shown in Figure 5.
In the left part of Figure 5, we show the temporal dynamics of changes in attenuation of the
Ce-doped (a) and Ce/Au-codoped (b) fibers under the action of 543 nm light, measured at the
same wavelength. The effect of partial bleaching of β-induced loss (the negative AD) is
apparent. Note that optical bleaching of both fibers demonstrates a saturating behavior and
that the decay rate is bigger for the fiber codoped with Au than for Au-free one (compare
curves 1–3 in (a) and (b)); also notice an almost exponential character of bleaching when the
process gets starting (see (d) on the right side of Figure 5). The bleaching effect is clearly
demonstrated by the photographs in Figure 5(c), exemplifying the case of Ce-doped fiber. It
is seen that its initial state (before β-irradiation) was almost restored under the action of 543
nm light: compare the photos in Figure 1(b) and Figure 5(c).
One would speculate on whether bleaching of the Ce-doped and Ce/Au-codoped fibers arises
solely due to laser-light-induced recombination or due to thermally assisted recombination,
too, but as for us, the former appears to play a vital role.
Figure 6(a) and (b) shows how the bleached (main frames) and unbleached (insets) loss in the
Ce-doped and Ce/Au-codoped fibers behave at 543 nm bleaching. Note that unbleached
(remnant) loss is bigger in Ce/Au- than in Ce-doped fiber, that is, codoping of a Ce-doped fiber
with Au results in a similar property of lesser susceptibility to exterior influence (compare with
the results on β-irradiation); however, in the case of bleaching this feature appears to be a
disadvantage.
The results of illuminating darkened Ce-doped and Ce/Au-codoped fibers with UV light are
shown in Figure 7. In Figure 7(a) we exemplify the spectral dynamics of transmission of βirradiated (at dose 5) Ce/Au-codoped fiber. The photographs in Figure 7(b) visualize the result
of treatment, being almost a full fading of IA loss. This effect can be quantified by a shift of
wavelength’s transmission, measured at a 3 dB level (see gray line in Figure 7(a)), from near-

Figure 6. Bleached (main frames) and unbleached (insets) spectral loss in Ce-doped (a) and Ce/Au-codoped (b) fibers
after ~0.5 mW 543 nm treatment, posterior to β-irradiation with doses 2 (curves 1), 4 (curves 2), and 6 (curves 3). For
comparison, curves 0 demonstrate the attenuation spectra of pristine fibers. (Reproduced with permission from Kir’ya‐
nov et al. [75]. Copyright© 2014, Optical Society of America).

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers
http://dx.doi.org/10.5772/63939

IR to VIS. It is seen from Figure 7(c), where we demonstrate the results of experiments with
Ce/Au-codoped (black open dots) and Ce-doped (gray open squares) fibers, that it has a similar
character for both fibers.

Figure 7. (a) Dynamics of attenuation decay (in terms of transmission of Ce/Au-codoped fiber under UV-lamp illumi‐
nation with maximal spectral power @350 nm). Bleaching was realized in the darkened fiber, posterior to β-irradiation
with dose 4. (b) Micro-photographs of darkened (dose 5 of β-irradiation) Ce/Au-codoped prior to optical bleaching
with UV-lamp (top) and after continuous bleaching during 10,000 h (bottom). (c) Examples of the spectral transforma‐
tions during UV-bleaching in terms of shifting of the fiber’s transmission edge wavelength measured at -3 dB level; the
data were obtained for Ce/Au-codoped (open black dots) and Ce-doped (open grey squares) fibers, preliminary β-irra‐
diated with dose 4; both the data are fitted to the eye by dotted red lines. (Reproduced with permission from Kir’yanov
et al. [75]. Copyright© 2014, Optical Society of America).

2.3. Discussion
2.3.1. Pristine fibers
Regarding pristine Ce-doped and Ce/Au-codoped fibers (Figure 1), apart from a strong growth
of absorption seen at shorter (VIS to UV) wavelengths (apparently connected with the presence
of Ce in valences Ce3+/Ce4+ [23, 24]), the other two points deserve mentioning, being (i)
monotonous growth of loss toward IR in both fibers (of not clear origin but inherent to Ce
doping since such trend is absent in the reference Ce free fiber) and (ii) a distinct peak at
~520 nm (~2.4 eV) in the absorption spectra of both fibers (but absent in the Ce free one). We
suppose that this peak has the same origin as band 2 risen at β-irradiation and located at ~2.4 eV
(see Figure 4). This feature has not been reported for bulk Ce-doped silica but is frequently
observed in Ce-doped fibers subjected to ionizing radiations [17, 24]. It can be related to quite
stable Ce3+h+ centers, or alternatively while hypothetically, to Ce4+e− centers (existence of which

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Radiation Effects in Materials

was not documented), but apparently not to sole Ce ions being in either trivalent or tetravalent
state. As for us, a more realistic cause for the existence of Ce3+h+ or/and Ce4+e− defect centers in
pristine fibers, attributable by the 520 nm peak, can be ionization, that is, generation of electrons
e− and holes h+, at the fiber preform’s collapse stage [24] or during the fiber’s drawing with
posterior covering by acrylic outer cladding when—in both situations—strong UV light is
produced, with a result being a trapping of free carriers by Ce3+/Ce4+ species.
2.3.2. β-irradiated fibers
Consider in more details the results of β-irradiation of Ce-doped and Ce/Au-codoped fibers
(Figures 2–4). The processes, involved at irradiating the fibers with the result being rise
followed by saturation of IA, described by the “stretched-exponent” law [14, 24, 26]), comprise:
(i) creating of secondary carriers (holes h+ and electrons e−) in the core-glass matrix by β
(primary) electrons and their trapping on such glass imperfections as Ce ions (Ce3+/Ce4+),
nonbridging oxygen centers, other centers associated with Al and P, and oxygen vacancies; (ii)
direct h+…e− recombination (annihilation); (iii) thermally or/and radiatively activated recom‐
bination between the centers or defects that have arisen during and after β-irradiation.
Concerning the role of Ce-doping, we assume that IA is produced via irradiation-induced
reactions Ce3++h+→Ce3+h+(→?Ce4+) and Ce4++e−→(?Ce4+e−)→Ce3+ [26–28], implying Ce was in
valences 3+/4+ in pristine fibers or/and being generated via irradiation. Note that determina‐
tion of relative contents of Ce3+/Ce4+ ions in the pristine state is hard and that at low Ce doping,
mainly fluorescing Ce3+ are formed in the core-glass, while at higher overall Ce concentration
both Ce3+ and Ce4+ (nonfluorescing) ions can be present. Unfortunately, the absorption spectra
of glasses containing both Ce3+/Ce4+ ions have the featuring bands within a 200–400 nm (UV)
range (not detectable by our spectral equipment); so any arguing about Ce3+↔Ce4+ transfor‐
mations for this range is impossible. In the meantime, the absorption bands of Ce3+h+ and Ce4+e
−
defect centers are expectedly located in VIS (see above), on one hand, and, on the other hand,
the detected spectral changes at β-irradiation occur in VIS, too (band 2); thus, formation of
metastable centers Ce3+h+/Ce4+e− as its result is a worthy proposal.
Furthermore, IA bands 1 (~3.0 eV) and 2 (~2.4 eV) (see Figure 4) have been undoubtedly
separated; see above. The first of them, in Ce-doped and Ce/Au-codoped fibers, has seemingly
the same origin as the one in the Ce-free fiber (see Figure 2), that is, it most probably belongs
to one, most simply organized, type of the two NBOHCs centers, inherent to silica. The other
would stem from Ce doping: it is seen from Figure 2 that such band does not exist in the
reference Ce-free fiber. However, the irradiated Ce-free fiber demonstrates ~600 nm band,
probably attributing the other type of NBOHCs [26], absent in both Ce-doped fibers subjected
to irradiation: compare spectra 1–3 shown in Figure 2. The fact that the dose dependences of
IA (Figure 4) have different characters for the fibers points on different nature of the centers
represented by bands 1 and 2. Therefore, our hypothesis that ~3.0 eV band stems from NBOHCs
and that ~2.4 eV one is associated with a Ce-related center (Ce3+h+/Ce3+e−) seems to be relevant.
In our case (alumino-silicate core glass of Ce-doped and Ce/Au-codoped fibers), such “point”
defects as Al-E’ and Al-oxygen-deficient centers can be also created at trapping secondary

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electrons and holes born at β-irradiation (phosphorous (P) presented in small amount plays a
little effect).
Thus, the processes roughly schematized as Ce3+↔Ce4+ seem to be a sole way to address the
spectral transformations seen from Figures 2–4 to happen via the formation in the Ce- and Ce/
Au-doped fibers of metastable states Ce3+h+/Ce4+e−. Furthermore, it deserves mentioning that
overall susceptibility to β-irradiation (overall IA loss) of Ce-doped fiber is higher than of
Ce/Au-codoped one. This may signify that the core glass containing gold is more stable than
that solely doped with Ce. On the other hand, deviations in the experimental data for kinetics
of IA versus β-irradiation dose for the fibers (refer to IA spectra in Figure 3 and to dose
dependences in Figure 4) are more pronounced in the former than in the latter fiber. A possible
explanation for this can be that codoping with Au gives rise to the core-glass system more
ordered. This property seems to have impact for establishing almost the same path kinetics of
defect centers’ formation as compared with other factors involved in such of type fibers.
2.3.3. Optically bleached fibers
Let us discuss now the effect of partial bleaching of β-irradiated Ce-doped and Ce/Au-codoped
fibers under the action of low-power VIS/UV light (see Figures 5–7). Whereas a doubtless
conclusion on its nature is hard, some discourse about the matters involved can be made. The
processes responsible for recombination of radiation-induced defects or color centers, seen as
IA fading (bleaching) of darkened fibers, can be of thermally and/or optically induced origin.
Bleaching, with its result being decreasing IA versus time, seems to be an example of mainly
optically induced recombination of both types of centers, NBOHCs and Ce-related Ce3+h+
(assumed to be represented by bands 1 and 2, respectively) ones.
As seen from Figure 5(d) and Figure 7(c), IA decreases almost exponentially at the beginning
of bleaching. However, within the whole interval of optical bleaching, IA in bands 1 and 2 is
seen to fade (in terms of negative AD at 543 nm illumination, see Figure 5(a, b), as well as in
terms of shifting the transmission edge to shorter wavelength, at exposure the fibers to UV
light, see Figure 7(a, c)), which obeys a “stretched exponent” law [26]. An explanation for this
behavior can be not only complexity of the mechanisms involved at optical bleaching but also
a fact of limited “penetration” of bleaching light into a fiber sample (especially in the case of
543 nm bleaching).
Concerning the essence of IA at optical bleaching, we can, at the current stage of our knowl‐
edge, propose them only tentatively. If our attribution of IA bands 1 and 2 as “signatures” of
NBOHCs and Ce-related Ce3+h+ centers is correct, then these centers, formed at trapping free
holes, should be breaking via the holes’ detrapping and annihilating with free electrons born
at interaction with VIS/UV light. Weak intensity of bleaching light is guessed to produce
mainly extra electrons rather than holes in the core-glass, leading to dominance of the processes
relating to the hole-trapped centers, such as NBOHC (~3.0 eV band) and Ce3+h+ ones (~2.4 eV
band). Note that a strong candidate to be “in-charge” of production of e− at the UV/VIS
excitation may be Ce3+ ions themselves [15].

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Radiation Effects in Materials

Comparison of the bleaching effect in Ce-doped (without Au codoping) and Ce/Au-codoped
fibers show that it is less expressed in the latter than in the former, which is probably related
to lower susceptibility to exterior influence of Ce/Au-codoped fiber (a consequence of its more
ordered glass network, already noticed).

3. Electron irradiation versus PD of Yb-doped germano-alumino-silicate
fibers: The effects comparison
Yb3+-doped silica fibers (YFs) with different core-glass hosts codoped with Al, Ge, or P have
been of considerable interest during the past decades as extremely effective media for fiber
lasers for the spectral region 1.0–1.1 μm, when pumped at 0.9–1.0 μm wavelengths. A variety
of diode-pumping configurations (core and cladding) and pump wavelengths were examined
so far, resulting in recognition of optimal arrangements for multi-watt release from YF-based
lasers with high optical efficiency ~70–75% and perfect beam quality [29, 30]. However, in spite
of a remarkable progress in the field, there remain obstacles that limit the performance of YFbased lasers, one of them being PD [31], that is, long-term (minutes to hours) degradation of
laser power, measured by units to tens %. This hardly mitigated disadvantage becomes notable
when dealing with a laser based on heavily doped YF where a high Yb3+ population inversion
is created, either at high-power continuous-wave or moderate-power pulsed lasing. A number
of studies were aimed to understand the PD phenomenon which however remained unclear,
although a few hypotheses have been proposed for its explanation [32–42].
On the other hand, a few studies aiming the characterization of susceptibility of YFs under
such irradiations as X-rays, γ-quanta, and UV have been reported [43–45]. The main motivation
was inspection of YF-resistance to harmful environments. In many cases, the excess-loss
spectra induced in YFs resemble the ones, characteristic for PD at resonant pumping into
Yb3+ resonant-absorption band, the fact undoubtedly deserving attention.
Here, the results of two sets of experiments, where susceptibility of YFs with similar germanoalumino-silicate glass-cores, doped with Yb in different concentrations to irradiation by a beam
of β-electrons and to resonant (into Yb3+ resonant band) optical pumping, are presented. In
both circumstances, qualitatively similar trends are revealed, being strong and monotonous
change in attenuation in VIS (darkening), accompanied by more complex transformations
within the resonant absorption band of Yb3+ ions, either upon dose (the case of β-electron
irradiation), or exposing time (the case of optical pumping at 977 nm). Below, we compare and
discuss the experimental results and attempt to explain them.
3.1. Fiber samples and experimental arrangement
The YFs inspected in these experiments were drawn from germano-alumino-silicate glass
preforms fabricated using the “conventional” MCVD/SD route. The attenuation spectra of the
fibers being in pristine (as-received) state are demonstrated in Figure 8(a).

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Figure 8. (a) Attenuation (small-signal absorption) spectra of fibers with low (YF-1), intermediate (YF-2), and high
(YF-3) Yb3+ contents: curves 1, 2, and 3, respectively. (b) Fluorescence spectra of the fibers at resonant 977 nm excitation
(pump power—300 mW). Labeling of curves 1, 2, and 3 is the same as in (a) and (b). Inset in (b) shows “cooperative”
fluorescence in VIS. (Reproduced with permission from Kir’yanov [76]. Copyright© 2011, Scientific Research Publish‐
ing Inc).

The concentrations of Yb3+ ions in the fibers differed by more than an order of magnitude, so
certain differences were expected after their exposure to β-electron irradiation (hereafter in
this paragraph—e-irradiation) and to optical pumping (hereafter—OP) at 977 nm wavelength .
The fibers, having the lowest, the intermediate, and the highest Yb3+ doping level, are referred
further to as YF-1, YF-2, and YF-3, respectively.
The essences of experiments on e-irradiation of the YFs were completely the same as at
irradiating the Ce-doped fibers (Paragraph 2). The indices “1,” “2,” and “3” label below the
doses 2 × 1012, 1 × 1013, and 5 × 1013 cm–2, respectively.
Experiments on OP at 977 nm were made in a similar way as described in Ref. [36]. YF samples
were pumped using a standard 300 mW 977 nm laser diode (LD). The pump light was launched
from LD to an YF sample under study through a splice. The end of the latter was spliced to a
piece of SMF-28 fiber that was, in turn, connected to an OSA for the transmission spectra’
measurements. In these experiments, we handled short (a few cm) pieces of YFs to ensure nolasing conditions and negligible contribution of amplified spontaneous emission of Yb3+.
The optical transmission spectra of the YF samples were obtained using a white light source
with a fiber output and the OSA, turned to a 1 nm resolution. These spectra were recorded
over the spectral range 400–1200 nm, where the most interesting spectral transformations occur
as the result of e-irradiation/OP. The output of the white light source was connected to a fiber
set containing an YF sample (pristine or subjected to e-irradiation/OP), while its attenuation
was measured using the OSA. The attenuation spectra were recorded before and after each
stage of e-irradiation (doses) or OP at 977 nm pumping (times). Lengths of the YFs were chosen
to be short enough, from <1 cm (YF-3) to tens cm (YF-1), to avoid spectral noise artifacts. In
some of the figures below, the difference (IA) spectra are demonstrated which were obtained
after subtracting the attenuation spectra of pristine samples from the ones taken after certain
dose/time of e-irradiation/OP. This allows insight to “net” spectral loss, established after
darkening of either type. All the spectra presented beneath have been obtained after recalcu‐
lating transmission coefficients in loss [dB/cm]. We also measured the fibers’ fluorescence

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Radiation Effects in Materials

spectra and fluorescence kinetics of Yb3+ ions before and after e-irradiation/OP, applying the
“lateral” geometry [46]. We used the same OSA for the fluorescence spectra measurements
and a Ge photodetector (PD) and oscilloscope for the fluorescence-decay measurements. In
the last case, LD power was modulated by a driver controlled by a function generator to achieve
square-shaped pulses with sharp rise and fall edges. The time resolution of the setup was 8 μs.
All the experiments were made at room temperature.
3.2. Experimental
3.2.1. E-irradiation
The attenuation spectra of samples YF-3 and YF-1, having correspondingly the highest and
lowest Yb3+ concentrations, obtained after different doses of e-irradiation, along with the
attenuation spectra of the samples in a pristine (dose “0”) state are shown in Figure 9(a, b).

Figure 9. Attenuation spectra of samples YF-3 (a) and YF-1 (b). The data are for e-irradiation doses increased from “0”
(pristine samples) through “1” and “2”–“3”. Insets show the difference spectra obtained after subtraction of the spectra
of pristine samples from the ones after e-irradiation of the samples. Dashed lines show the positions of wavelengths
for which the data in Figure 10 are built. (Reproduced with permission from Kir’yanov [76]. Copyright© 2011, Scientific
Research Publishing Inc).

First, a notable increase of background loss in VIS with increasing e-irradiation dose is revealed
(see main frames of Figure 9). Also notice a specific spectral character of this loss for both fibers,
viz. a drastic rise of loss-magnitude toward shorter wavelengths. This is a well-known for
Yb3+-free silica fibers’ trend in experiments on various kinds of irradiations. At the same time,
apparent differences are seen in magnitude of e-irradiation-induced loss in these two fibers,
that is, a higher degree of darkening in YF-3 than in YF-1. (For YF-2, intermediate in Yb3+ doping
level, the effect of e-irradiation is intermediate, as compared with YF-3 and YF-1.]
Second, detectable but less pronounced spectral transformations are revealed for the resonantabsorption band of Yb3+ (850–1100 nm) (see insets to Figure 9), where the difference spectra

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are shown, obtained as explained above. Very weak in YF-1 (Figure 9(b)), the spectral trans‐
formations are noticeable in YF-3 (Figure 2(a)). These changes seem to be a result of some
process, associated with e-irradiation of the fibers, which affects concentration of Yb3+ ions.
More details are seen in Figure 10 where we plot the results for samples YF-1 (a) and YF-3 (b),
taken for all doses. Figure 10(a, b) demonstrates how attenuation within the resonantabsorption of Yb3+ ions (peaks at 920 and 977 nm, see also Figure 8(a)) changes throughout eirradiation: see curve 1 (for the 977 nm peak) and curve 2 (for the 920 nm peak), respectively.
A decrease followed by an increase in the magnitude of small-signal absorption arises in both
peaks with dose increasing in YF-3 (heavier doped with Yb3+); this trend is, in contrast, less
expressed in YF-1 (lower doped with Yb3+).
For comparison, we plot in Figure 10 the changes in attenuation of YF-3 (c) and YF-1 (d) fibers
in VIS, where background (nonresonant) losses arise as the result of e-irradiation. Here we
limit ourselves by the data, counted for 500 (curve 3) and 633 (curve 4) nm. It is seen that
background loss steadily grows with dose, a common effect for silica fibers. Note that the rate
of growth is higher in YF-3 than in YF-1. Furthermore, an initial level of background loss in
pristine YF correlates with initial content of Yb3+ ions.

Figure 10. Dose dependences of attenuation in resonant-absorption Yb3+ peaks centered at 977 (curves 1) and 920
(curves 2) nm (top panels) and in VIS, for wavelengths 500 (curves 3) and 633 (curves 4) nm (bottom panels). The data
are for samples YF-3 (a, c) and YF-1 (b, d). (Reproduced with permission from Kir’yanov [76]. Copyright© 2011, Scien‐
tific Research Publishing Inc).

Figure 11(a) and (b) gathers the experimental data obtained using all fibers, YF-1, YF2, and
YF-3. From Figure 11(a), it is seen that a monotonous increase of nonresonant loss in VIS
(darkening), exampled by wavelengths 500 and 633 nm, with increasing Yb3+ concentration;

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Radiation Effects in Materials

the latter is proportional to YF small-signal absorption at 977 nm. This demonstrates that the
presence of Yb3+ dopants gain their degradation at e-irradiation. (Here we show the results
obtained at dose “3” only, because for other doses the dependences are similar, given by a
smooth dependence of induced loss in VIS versus e-irradiation dose (see Figure 10(c, d)). From
Figure 11(b), it is seen that the lowest levels to which the values of absorption in the 977 nm
peak approach throughout e-irradiation (minima of curves 1 in Figure 9) decrease with
increasing Yb3+ content (a similar trend is observed for the other peak of Yb3+, at 920 nm). This
fact seems to be in favor of that initial concentration of Yb3+ ions in pristine samples substan‐
tially decreases as a result of e-irradiation, at the primary stage. However, at the following
stages, Yb3+ concentrations are re-established on levels comparable with those in pristine YFs
(refer to Figure 10(a)). [The remainder of Figure 11(c, d) provides the data, obtained in the
experiments on OP of the YFs, reported below.]

Figure 11. The results of experiments with fibers YF-1, YF-2, and YF-3, which were obtained for different e-irradiation
doses (a, b) and OP times (c, d). The data are for the resonant-absorption peaks at 977 and 920 nm (filled and empty
asterisks) (b, d)) and for the VIS region, exampled by wavelengths 500 nm (crossed squares) and 633 nm (crossed cir‐
cles) (a, c). Dotted lines are for visual purposes only. (Reproduced with permission from Kir’yanov [76]. Copyright©
2011, Scientific Research Publishing Inc).

3.2.2. PD at OP
We report here the results of OP experiments for sample YF-3 mainly (see Figures 12–14),
having the biggest content of Yb3+ ions. Then, we summarize all the results, obtained for YF-1,
YF-2, and YF-3 fibers, in Figure 11(c, d).

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Figure 12. Attenuation (small-signal absorption) spectra of fiber sample YF-3 after OP @ 977 nm. The data are for a
pristine sample (curve 1: “0 min”) and for photo darkened samples (curves 2 and 3, obtained after 40 and 150 min of
OP, respectively). Dashed lines show the positions of wavelengths for which the data in Figure 13 are built. (Repro‐
duced with permission from Kir’yanov [76]. Copyright© 2011, Scientific Research Publishing Inc).

Figure 13. Dose dependences of attenuation in resonant-absorption (Yb3+) peaks centered at 977 (curve 1) and 920
(curve 2) nm (a) and in VIS, for wavelengths 500 (curve 3) and 633 (curve 4) nm (b). The data are for sample YF-3.
(Reproduced with permission from Kir’yanov [76]. Copyright© 2011, Scientific Research Publishing Inc).

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Radiation Effects in Materials

Figure 14. Difference attenuation spectra after dose “3” of e-irradiation (curve 1) and after 2 h of OP at 977 nm (pump
power is 300 mW) (curve 2); curve 3 is the difference of spectra 1 and 2. The data are for sample YF-3. (Reproduced
with permission from Kir’yanov [76]. Copyright© 2011, Scientific Research Publishing Inc).

Figure 12 shows the attenuation spectra of sample YF-3 (length, 0.8 cm) after 40 and 120 min.
of OP. The LD power was fixed in these experiments at 300 mW, the highest in our circum‐
stances level of Yb3+ ions inversion. For comparison, the attenuation spectrum of pristine
(0 min) sample YF-3 is shown in Figure 12, too. Once compared with the attenuation spectra
after e-irradiation (refer to Figure 9(a)), these spectra are seen to be similar. That is, a substantial
increase of background loss is observed in VIS with increasing OP-time (the PD effect). Note
that the spectral “signature” of PD resembles the one after e-darkening (see Figure 9).
In Figure 13(a), we demonstrate the results of the experiments with sample YF-3, obtained at
increasing OP time. Their representation is similar to the one used at the description of
experiments on e-irradiation (see Figure 10(a)). From Figure 13(a), it is seen how attenuations
in the two absorption peaks of Yb3+ ions (at 977 and 920 nm) change throughout OP; see curves
1 and 2, respectively. The time dependence of OP-induced changes at 977 nm resembles the
dose dependence at e-irradiation of sample YF-3. However, curve 1 in Figure 13(a) has
“asymmetric” shape versus OP time, differing from “symmetric” shape of the dose depend‐
ence at e-irradiation given by curve 1 in Figure 10(a). Furthermore, the time dependence of
OP-induced changes at 920 nm, see curve 2 in Figure 13(a), is very weak, being completely
different from curve 2 in Figure 10(a) (e-irradiation). Therefore, we can propose that different
mechanisms, responsible for the induced changes in the resonant-absorption band of Yb3+ at
977 and 920 nm, stand behind these two (e-irradiation and OP) treatments of the fibers.
In Figure 13(b), we demonstrate the results of spectral transformations arising in YF-3 in VIS,
at OP. Again, we provide in Figure 13(b), the data for a couple of wavelengths, 500 (curves 3)
and 633 (curves 4) nm, as most representative. In contrast to the dose dependences at eirradiation, long-term OP at 977 nm results in completely different dynamics of background
loss in time. Indeed, it is essentially nonlinear versus time: there is a short timing interval in
the beginning (few minutes) where PD increases dramatically, while afterward (tens of
minutes) it slows down and tends to saturate.

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Figure 14 allows one to compare the attenuation spectra for YF-3 suffered dose “3” of eirradiation (curve 1) and 2 h of OP (curve 2). The spectra look qualitatively similar, which may
tell that the mechanisms involved are similar in these two circumstances. At the same time, if
one spectrum is subtracted from another, the result (curve 3 in Figure 14) brings some news.
That is, apart from the difference presented in VIS (in background loss), there is a feature in
the Yb3+ resonant band: though no deviation from “plain” behavior of curve 3 is seen near 920
nm peak of Yb3+, there is a well-defined (negative) 977 nm peak (it is marked by a dotted ring).
This detail seems to be important as it lightens nonhomogeneity within the Yb3+ resonantabsorption band near 977 nm, present at OP but not—at e-irradiation.
This detail becomes expressed more when one analyzes the data obtained at PD of the other
fibers, YF-1 and YF-2 (see Figure 15). In this figure, where we plot the difference spectra
obtained for these fibers, analogous but clearer seen detail appears exactly within the 977 nm
peak of Yb3+ ions (it is marked by a dotted ring in (a) and (b)).

Figure 15. Difference loss spectra of YF-1 (a) and YF-2 (b), obtained after 1 h of OP at 977 nm. (Reproduced with per‐
mission from Kir’yanov [76]. Copyright© 2011, Scientific Research Publishing Inc).

Let us return to Figure 11(c, d), where we gather the results on OP for all YF samples.
In contrast to the results on e-irradiation (Figure 11(a, b)), one can reveal first nonlinear growth
of background loss at 500 and 633 nm with increasing Yb3+ concentration (Figure 11(c)).
Apparently, this behavior is different from linear growth of background loss at e-irradiation
(Figure 11(a)). Second, it is seen that, instead of a linear decrease of the resonant peaks at 977
and 920 nm with dose (occurring at primary stages of e-irradiation—see Figure 11(b)), a
nonlinear law is obeyed by a decrease of the resonant peak at 977 nm while almost no change
happens with the peak at 920 nm (Figure 11(d)).
Thus, the situation with OP-induced spectral transformations in the YFs is complex and
curious at first glance. The 977 nm peak is strongly affected by OP, not the 920 nm one. This
can be explained by the presence in the fibers of some other centers than Yb3+ dopants, but
closely related to them and spectrally matching them near 977 nm. Moreover, partial weight
of such centers in YF-core is expected to increase with increasing Yb3+ ions concentration. The
nonlinear behavior of the nonresonant background loss versus OP time, discussed earlier (see
Figure 13(b)), seems to be a related phenomenon.

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Radiation Effects in Materials

3.2.3. What’s about fluorescence?
The fluorescence spectra obtained using pristine YF-1, YF-2, and YF-3 fibers at 977 nm pumping
are shown in Figure 8(b). All these are similar in appearance and their intensities are propor‐
tional to Yb3+ ions concentrations in the fibers (The measurements were made at the same
conditions and at the same pumps.)
We also measured the fluorescence spectra of the YFs after irradiation by an electron beam
and after long-term OP at 977 nm, but almost no qualitative spectral changes were captured
in the Yb3+ fluorescence band; so we don’t provide them here. We could only notice a small
decrease in the fluorescence power as the result of the treatment, but this trend could not be
quantified. Furthermore, it was found that the characteristic Yb3+ fluorescence decay time
slightly decreases in the set of pristine YFs. This is a result of the presence of two exponents in
the fluorescence kinetics, measured by ~0.7 and ~0.2…0.3 ms. Note that insignificant growth
of the latter contribution was detected for the fiber with the highest Yb3+ content (YF-3); see
also Ref. [46–48]. However, the time constants obtained at fitting were nonaffected neither by
e-irradiation nor by long-term OP. Concluding, we can reveal that none, or very insignificant,
changes occurred in the YFs in the sense of Yb3+ fluorescence.
3.3. Discussion
Summarizing all the data, we notice that either at e-irradiation or at resonant OP substantial
and complex but different in appearance changes arise within the resonant absorption band
of Yb3+ ions (“reversible bleaching”), while monotonous growth of nonresonant background
loss is observed in VIS (“darkening”). Furthermore, these trends are revealed to stem from the
changes in concentrations of Yb3+ ions and, seemingly, of other centers, closely related to them
and spectrally matching them near 977 nm. This is the main news of this study.
A general consequence of the experiments on e-irradiation, rise of background nonresonant
loss in YFs in VIS (see Figure 10 (c, d)), is not surprising. This loss correlates spectrally with
the excess loss arising in optical fibers at other types of irradiation (X-rays, γ-quanta, UV [33–
35]). Some other aspects are as follows:
1.

A monotonic increase of the background loss in VIS (darkening) with increasing Yb3+
content in the YFs, which demonstrates that the presence of Yb3+ dopants leads to a higher
degree of the fibers’ degradation at e-irradiation (Figure 11(a)).

2.

A notable decrease followed by equally notable increase arising in the resonant-absorption
peaks of Yb3+ (at 920 and 977 nm) with increasing e-irradiation dose (Figure 10 (a, b)), the
effect also dependent on Yb3+ concentration (Figure 11(b)).
Thus, the presence of Yb3+ dopants in the fibers results in a more pronounceable degra‐
dation at e-irradiation, with a probable reason being that Yb3+ ions are powerful sources
of secondary carriers (electrons and holes) born at e-irradiation. That is, the changes within
the resonant-absorption band of Yb3+ may stem from excitation of inner-shell (f) electrons
of Yb3+ and their valence transformation through the charge-transfer (CT) processes (direct
and reversed), sketched by the following reactions [36]: e- + Yb3+ → Yb2+; e+ + Yb2+ → Yb3+,

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where e– and e+ stand for secondary (irradiation induced) electrons and holes, and Yb2+ is
the notation for Yb ions in 2+ valence state. In turn, the presence in the fibers of secondary
carriers as the result of e-irradiation can produce such defects as oxygen-deficit center
(ODC) and NBOH centers [47]. These centers are known to be responsible for the wide
excess-loss spectral bands similar to the ones produced in the darkened fibers (Fig‐
ures 9 and 14).
Qualitatively similar observations can be made regarding the spectral transformations in
the YFs as the result of OP at 977 nm (refer to Figure 11(c, d) and Figures 12–15). Analo‐
gously, the following trends are drawn:
3.

Background loss in VIS substantially grows at long-term OP (see Figures 12 and 13(b))
while its character is typical for PD in YFs [31–41]. However, an increase of this loss in VIS
with increasing small-signal absorption has, in contrast to e-irradiation, a nonlinear law
(Figure 11(c)), thus revealing an almost quadratic dependence versus Yb3+ concentration.

4.

The dependences of resonant absorption, measured in the peaks of Yb3+ at 977 and 920 nm
upon OP time, have essentially different characters (Figure 13(a)). If the absorption
coefficient in the 977 nm peak changes by a law similar to the one at e-irradiation, the
absorption coefficient in the 920 nm peak is virtually constant throughout long-term OP.
The concentration dependences shown in Figure 11(d) tell us more: the changes in these
peaks with increasing content of Yb3+ ions are also different. We cannot interpret these
details in terms of simple concentration dependences in regard to Yb3+ ions. Otherwise,
an assumption can be made instead that the changes in the 977 nm peak are related to the
changes in concentration of some others than Yb3+ ions centers but spectrally matching
them in the 977 nm peak.

5.

The spectral signature of the latter is seen from Figures 14 and 15 where the difference
attenuation spectra after OP are demonstrated. One can see from these figures that the PD
effect (growth of nonresonant loss in VIS) is accompanied by bleaching of the resonant
peak at 977 nm, whereas none happens with the peak at 920 nm. Note that a similar feature
was reported earlier for the other type of YF, fabricated by the DND method [36].

The observations (3–5), when gathered together, tell us that PD in the YFs at high-power, longterm OP at 977 nm arises among the centers concentration of which is a nonlinear (almost
quadratic) function of Yb3+ ions concentration. These are most probably the centers composed
of couples of Yb3+ ions (pairs), or agglomerates of the latter. Furthermore, similar reactions: e+ Ybp3+ → Ybp2+; e+ + Ybp2+ → Ybp3+ (see above) can be proposed to address these transformations
at OP, where index p stands to show that a pair of Yb3+ ions is involved in the processes and
notations e– and e+ are used for an electron and a hole, free or trapped by the nearest ligand,
say oxygen. Such reactions can go at the assistance of CT-processes between ion pairs where
both constituents are in the excited state. Hence, the spectrally wide background loss (PD) in
the fibers (see Figures 12 and 14) can be produced Ybp2+ and of e–/e+-related centers (say, ODCs
and NBOHCs) at OP, like this takes place at e-irradiation.

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Radiation Effects in Materials

It is currently accepted that PD occurs among clusters of Yb3+ ions (obviously, pairs are their
kind). However, a novelty found here is the spectral feature, occurring at OP (see dotted rings
in Figures 14 and 15) but not—at e-irradiation.
There are evidences for that PD can be itself associated with nonbinding oxygen near surfaces
of Yb/Al clusters that can be formed in alumino-silicate glass (our case). The nonbinding
oxygen originates from Yb3+ substituting Si4+ sites. When subjecting a YF to 977 nm OP, the
excess energy is radiated as phonons, causing a lone electron of a nonbinding oxygen atom to
shift to a nearest neighbor nonbinding oxygen atom with creation of a hole and a pair of lone
electrons, which results in a Coulomb field between the oxygen atoms to form an unstable
“color” center. Conversion of such an unstable center to a semistable center requires shifting
of one electron of the lone electron pair to a nearest neighbor site. As a result of this, the
formation of Yb-related ODC can happen. On the other hand, PD in alumino-silicate YFs may
take place via breaking of ODC, which gives rise to release of free electrons. The released
electrons may be trapped at Al or Yb sites to form a color center resulting in PD. These
hypotheses can serve as the arguments, bringing more clarity in understanding the similarity
of the spectral transformations in YFs at e-irradiation (creation of “secondary” carriers by βelectrons) and at OP (creation of carriers and color centers by pump-light).

4. Effect of electron irradiation upon optical properties of Bi-doped silica
fibers
Bi-doped silica fibers with core-glass codoped with Al, Ge, or P are currently of increasing
interest, being a promising active medium for amplifying and lasing in the spectral range 1.1–
1.6 μm (see e.g. [49–59]). In spite of remarkable success in the field, there remain certain
obstacles for further improvements of Bi fiber lasers and amplifiers because the main problem
is lack of clarity in the nature of Bi “active” centers (Further—BACs) in silica glass. Thus, any
research aiming to recover the essences of BACs would have value.
Below we highlight the effect of irradiation of Bi-doped germano- and alumino-silicate fibers
by a beam of free electrons of high energy. The main result of the treatment was found to be
decrement (“bleaching”)/increment (rise of resonant absorption) in the characteristic peaks,
being ascribed to BACs in Bi-doped germano-silicate/alumino-silicate fibers. (Note that
analogous trends were reported for similar fibers and glasses under the action of UV laser
pulses and γ-quanta [60, 61]). Given that the other optical properties of the fibers under scope,
such as BACs fluorescence spectra and lifetimes, were found to be weakly affected by electron
irradiation, the changes in the absorption spectra should be associated with the changes in
BACs concentration, as firmly justified in our study.
4.1. Fiber samples and experimental arrangement
The Bi-doped silica fibers were drawn from Ge and Al codoped silicate-glass preforms,
fabricated applying the MCVD/SD technique. Core radii of the fibers were measured to be in
the 2…3 μm range. The representative attenuation spectra of pristine (as-received) Bi-doped

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers
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germano- and alumino-silicate fibers, having comparable contents of BACs, are shown in
Figure 16. Hereafter, the emission-active BACs are referred to as Bi(Ge,Si) and Bi(Al), respec‐
tively, in these two types of fiber. Impact of electron irradiation on the basic characteristics of
the fibers, referred to further as Bi-1, Bi-2, and Bi-3 (germano-silicate) and Bi-4 (aluminosilicate), is addressed subsequently.

Figure 16. Attenuation spectra of typical Bi-doped germano-silicate (curve 1) and alumino-silicate (curve 2) silica fi‐
bers. Arrow shows the pump wavelength (977 nm) used in the experiments on fluorescence spectra and lifetimes
measurements. Dashed lines show schematically a trend of the background loss to grow toward shorter wavelengths.
(Reproduced with permission from Kir’yanov [67]. Copyright© 2011, Optical Society of America).

Electron irradiation of Bi-1…Bi-4 fibers was proceeding in the conditions, described in
Introduction; the indices “1,” “2,” and “3” label to doses 2 × 1012, 1 × 1013, and 5 × 1013 cm–2,
respectively. The technique applied to reveal the spectral transformations in attenuation of the
Bi-doped fibers as the result of irradiation was completely the same as described in Paragraphs
2 and 3 and is not repeated here. When measuring Bi-related fluorescence, we utilized the same
LD (pump wavelength, 977 nm) for excitation. As seen from Figure 16, the pump wavelength
was on the Stokes tail of the 750–950 nm absorption band of BACs in Bi-doped germano-silicate
fiber and, correspondingly, on the anti-Stokes slope of the absorption band (centered at
1050 nm) of BACs in Bi-doped alumino-silicate fiber. We applied in the BACs fluorescence
measurements the lateral detecting geometry, when it was collected from the surface of a Bidoped fiber sample; the same OSA and a Ge PD were handled to proceed the fluorescence
measurements.
4.2. Experimental
The experimental results are presented by Figures 17–21. The attenuation spectra of Bi-doped
germano-silicate fiber sample Bi-2 subjected to electron irradiation with doses “2” and “3” are
shown in Figure 17(a) along with the attenuation spectrum of a pristine (dose “0”) fiber of the
same type. A strong irradiation-induced bleaching effect can be revealed from the figure, seen
as drop of magnitude of the absorption peaks labeled “1” (the 750–950 nm band) and “2” (the

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Radiation Effects in Materials

Figure 17. (a) Attenuation spectra of Bi-doped germano-silicate fiber sample Bi-2 obtained before (dose “0”) and after
(doses “2” and “3”) irradiation. The spectral area, comprising the resonant-absorption peaks “1” and “2” which attrib‐
ute Bi(Ge,Si) centers in the host glass, is shown (b) Insight to the spectral area of peak “2” in a vaster scale. (Repro‐
duced with permission from Kir’yanov [67]. Copyright© 2011, Optical Society of America).

Figure 18. Attenuation spectra of Bi-doped germano-silicate fibers Bi-1 (curves 1 and 2) and Bi-3 (curves 3 and 4), ob‐
tained before (dose “0”) and after (dose “3”) electron irradiation. [The spectral area for the peak “1” is zoomed.] (Re‐
produced with permission from Kir’yanov [67]. Copyright© 2011, Optical Society of America).

1250–1450 nm band). It is accompanied by an increase of background loss at shorter wave‐
lengths (refer to the left side of Figure 17(a)), a well-known feature in experiments on influence
of various type of irradiations on optical properties of Ge-doped silica fibers (see e.g. Refs. [62–
66]). Unfortunately, such a drastic growth of background loss did not allow us to make wellresolved measurements of the irradiation-induced transformations of BACs band peaked at
~500 nm (see Figure 16), so we inspected mostly the changes in peaks “1” and “2”. Also notice
that almost no changes arise in the attenuation peak at 1180 nm, which corresponds to the
cutoff wavelength: this and other Bi-doped germano-silicate fiber samples were drawn to
provide single-mode propagation for wavelengths >1200 nm.

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers
http://dx.doi.org/10.5772/63939

Figure 19. Dose dependences of attenuation of the resonant-absorption peaks “1” (~820 nm) (a) and “2” (~1400 nm) (b):
The data for Bi-1 (curves 1), Bi-2 (curves 2), and Bi-3 (curve 3) are shown. (c) insights dose dependences of the peaks
magnitudes’ ratios (820…1400 nm – curve I and 500…1400 nm – curve II), for fibers Bi-1 (circles) and Bi-2 (squares).
(Reproduced with permission from Kir’yanov [67]. Copyright© 2011, Optical Society of America).

Figure 20. Dose dependences of background loss measured at 700 nm for fibers Bi-1 (1), Bi-2 (2), and Bi-3 (3). (Repro‐
duced with permission from Kir’yanov [67]. Copyright© 2011, Optical Society of America).

Figure 21. Attenuation spectra of Bi-doped alumino-silicate fiber Bi-4, obtained before (curve 1, dose “0”) and after
(curve 2, dose “3”) electron irradiation. A part of the spectra is shown where the main resonant-absorption peaks of
Bi(Al) centers are observed. Inset highlights the behavior of one of the peaks (at ~700 nm) against the irradiation dose.
(Reproduced with permission from Kir’yanov [67]. Copyright© 2011, Optical Society of America).

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Radiation Effects in Materials

Of separate interest is the behavior of absorption peak “2.” Since absorption of BACs in this
spectral area is covered by an absorption peak of OH groups (1385 nm), we found reasonable
to zoom the spectral transformations for this range (see Figure 17(b)). From the figure, it is
seen that the contribution in attenuation which comes from contaminating by OH groups is
unchanged after irradiation, while the one stemming from the presence of the Bi-dopants is
substantially reduced.
One more example of the irradiation-induced bleaching effect is given in Figure 18 where we
make insight to the spectral transformations in the absorption peaks within the 750–950 nm
band (“1”) after electron irradiation of the rest of Bi-doped germano-silicate fibers, Bi-1 and
Bi-3. These two have, in pristine state, a higher and lower than Bi-2 concentration of BACs,
correspondingly (see Figure 17). The spectra shown in Figure 18 have been obtained before
(dose “0”: black curves 1 and 3) and after (dose “3”: blue curves 2 and 4) electron irradiation.
Qualitatively, the same law, viz., bleaching of the resonant-absorption peaks through the
interval 750–950 nm as the result of electron irradiation, is revealed, now for fiber samples Bi-1
and Bi-3. Hence, the bleaching effect is found to be a general essence of the Bi-doped germanosilicate fibers.
The next graphs plotted in Figure 19 (a, b) demonstrate how absorption peaks “1” (namely,
its main subpeak centered at 820 nm) and “2” (the one centered at ~1400 nm) are reduced via
electron irradiation (these dose dependences are shown for all fibers: Bi-1, Bi-2, and Bi-3). The
initial absorption values (in peaks; these are given near each curve in Figure 19(a, b)) were
taken from the attenuation spectra of pristine (dose “0”) samples. Curves 1–3 for resonantabsorption peaks “1” (Figure 19(a)) and “2” (Figure 19(b)) were obtained from the spectra
shown in Figures 16 and 17 after subtracting the background loss, which grows at irradiation
(refer to Figure 16 and also to Figure 20). Note that, for fiber Bi-3 characterized by the lowest
content of Bi centers, the data are provided for peak “1” only because the measurements for
peak “2” were below the resolution limit. It is seen from Figure 19(a, b) that bleaching of the
resonant-absorption bands after electron irradiation is a characteristic feature of the Bi-doped
germano-silicate fibers. Furthermore, resonant absorption bleaching in peaks “1” and “2” has
almost the same character, which is evident from Figure 19(c) where we plot the ratio of
absorption coefficients in peaks “1” and “2” in function of irradiation dose for Bi-1 and Bi-2
samples; see curve I. As seen, this quantity is kept virtually unchanged via irradiation, being
equal to its initial value measured in pristine state. The same conclusion can be made for the
ratio of absorption coefficients in peaks at ~500 nm and ~1400 nm (“2”), see curve II in
Figure 19(c). This is a justification of that resonant-absorption bands peaked at ~500, ~820, and
~1400 nm (and accordingly emission-active BACs attributed by these peaks, see Figures 16–
18) are affected by the same or by a very similar manner by electron irradiation.
Then, as seen from Figure 20, the background loss (measured in the dip at 700 nm, between
the absorption peaks ascribed to BACs in germano-silicate fiber; see Figure 17) monotonously
increases with dose, a common effect for all kinds of Ge-doped silica materials. (Growth of the
background loss is even more pronounceable in the UV.)
The results of electron irradiation of the Bi-doped alumino-silicate fibers (exemplified for fiber
Bi-4) deserve a separate attention. Figure 21 shows how the attenuation spectra of this fiber

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers
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are changed after a maximal dose of electron irradiation. It is seen from a direct comparison
of curves 1 and 2 (obtained before and after irradiation) that in the Bi-doped aluminate fiber
an opposite (to the case of the Bi doped germanate fiber) trend exists, viz. instead of resonantabsorption bleaching (see Figures 17–19), weaker but detectable extra absorption arises in the
peaks centered at ~520 and ~700 nm. Inset to Figure 21 examples the dynamics of the absorption
peak at ~700 nm upon dose; note that almost the same dose behavior is observed for the peaks
at ~520 and ~1050 nm.
We do not present here the results of measuring fluorescence spectra and fluorescence lifetimes
adherent to BACs, obtained before and after irradiation; the reader is advised to refer to [67]
for details. The only thing to mention in this regard is that the fluorescence spectra of both
types of the Bi-doped fibers (germano- and alumino-silicate) were not affected qualitatively
by electron irradiation, with a sole result of the latter being a decrease/increase of integrated
fluorescence power emitted by the germano-/alumino-silicate fibers. Also note that almost no
change was detected in the fluorescence kinetics for pristine and irradiated fibers of these two
types (0.38 ± 0.03/0.89 ± 0.04 ms). Thus, the changes in the resonant-absorption peaks, detected
above, should be related to a decrement/increment of the BACs concentration in the germa‐
nate/aluminate Bi-doped fibers.
4.3. Discussion
First of all, the attenuation spectra of typical pristine Bi-doped germano- and alumino-silicate
fibers (Figure 16) need examination. From these spectra that cover an extended wavelengths
interval (400–1600 nm), one can recognize the “fingerprints” of Bi dopants in the fibers,
appearing through the correspondent resonant-absorption bands: these were referred to as
Bi(Ge,Si) and Bi(Al) centers. Specifically, the main absorption peaks at 520, 700, and 1050 nm
(the Bi-doped alumino-silicate fiber) seem to belong to the center Bi(Al), whereas the ones at
500, 820 (910), and 1400 nm (the Bi-doped germano-silicate fiber)—to physically similar Bi(Ge)
and Bi(Si) BACs. Note that the peaks at 1400 nm look indistinguishable for both fiber types;
so they can be related to Si forming host of both the glasses (see e.g. Refs. [68, 69]). (Other
spectral features not linked to the presence in the fibers of Ge, Al, and Si originate either from
contaminating by water (OH peaks at 1385 and 1240 nm) or from special design of the fibers
(the cutoff peaks). Regarding the experimental results on electron irradiation, they are
remarkable but not enough to make a definite conclusion on real processes involved. The only
thing to propose is possible correlation of the rise and decrease of IR emission-active BACs
concentrations after electron irradiation in alumino- and germano-silicate fibers, respectively,
with known facts that substitutional four-coordinated Al in alumino-silicate glass is a hole
trap, whereas substitutional Ge in germanate glass is an electron trap [64, 66, 70–72]. This
difference can strongly affect the residuary charge state of the Bi specie after the electron
irradiation. The process of radiation-induced charge trapping of both electrons and holes can
be accompanied by the formation of different point defects (say, Ge(1), Ge(2), GeE’, Al-E’, and
Al-ODCs [73, 74]), detectable in ESR and optical spectra’ measurements.

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Radiation Effects in Materials

5. Concluding remarks
Resuming, we have shown in this chapter that a diversity of effects can be encouraged at
irradiating optical silica-based fibers with dopants of different kinds by high-energy βelectrons. This has been demonstrated on the examples of Ce- and Ce(Au)-doped aluminophospho-silicate fibers, Yb-doped germano-alumino-silicate fibers, and Bi-doped germanoand alumino-silicate fibers. The data presented in this Chapter is a collection of our recent
results, published in and in part reproduced from Refs [67, 75, 76]. In each case, unavoidable
“darkening” of the fibers in VIS arises as the main feature of electron-irradiation. Meanwhile,
such treatment allows one to detect interesting laws in transformations that “active” dopants
presented in the fibers suffer as well as to propose mechanisms responsible for the phenomena
involved. Also note that the new knowledge arising as the result of considering these trans‐
formations can be helpful for some applications of these or other doped fibers in such areas as
dosimetry (on nuclear plants) and space technology and can be as well valuable when
designing fiber devices (lasers and amplifiers) for the next-day telecom systems.

Acknowledgements
The author sincerely acknowledges the following people, contributing in the researches
highlighted above: Dr. N.S. Kozlova (National University of Science and Technology (MISIS),
Moscow, Russia)—for assistance in electron irradiation of all fibers; Drs. M.C. Paul and S.
Ghosh (Central Glass & Ceramic Research Institute, Kolkata, India)—for providing samples
of Ce and Ce(Au)-doped fibers and for discussions; Drs. V.V. Dvoyrin, V.M. Mashinsky, and
E.M. Dianov (Fiber Optics Research Center of the Russian Academy of Sciences, Moscow,
Russia)—for providing samples of Bi-doped fibers and valuable discussions; Dr. Yu.O.
Barmenkov (Centro de Investigaciones en Optica, Leon, Mexico)—for participating in experi‐
ments with Ce and Ce(Au)-doped fibers and useful discussions. The author also thanks
support from the Ministry of Education and Science of the Russian Federation under the
“Increase Competitiveness Program of NUST «MISiS»” (Grant К3-2015-056).

Author details
Alexander V. Kir’yanov
Address all correspondence to: kiryanov@cio.mx
Centro de Investigaciones en Optica (Center for Optical Researches), Leon, Guanajuato,
Mexico

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http://dx.doi.org/10.5772/63939

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Chapter 2

Radiation Effects in Optical Materials and Photonic
Devices
Dan Sporea and Adelina Sporea
Additional information is available at the end of the chapter
http://dx.doi.org/10.5772/62547

Abstract
The chapter continues previous reviews on radiation effects in optical fibers and on the
use of optical fibers/optical fiber sensors in radiation monitoring, published by InTech
in 2010 and 2012, by referring to radiation effects in optical materials, with an empha‐
sis on those operating from visible to mid-IR, and on some photonic devices such as
optical fibers for amplifiers, fiber Bragg gratings and long period gratings. The focus is
on optical materials and fiber-based devices designed for both terrestrial and space‐
borne applications. For the presented subjects, an overview of available data on Xrays or gamma rays, electron beams, alpha particles, neutrons, and protons effects is
provided. In addition, comments on dose rate, dose, and/or temperature effects on
materials and devices degradation under irradiation are mentioned, where appropri‐
ate. The optical materials and photonic devices reliability under ionizing radiation
exposure is discussed as well, as the opportunities to use them in developing radia‐
tion sensors or dosimeters. The chapter includes an extensive bibliography and
references to last published results in the field. Novel proposed applications of photonic
devices in charged particle beam diagnostics, quasi-distributed radiation field mapping
and the evaluation of radiation effects in materials for mid-IR spectroscopy are briefly
introduced to the reader.
Keywords: radiation effects, optical materials, optical fibers, fiber Bragg grating, long
period grating

1. Introduction
The goal of this chapter is to continue previous reviews on radiation effects in optical fibers [1]
and on the use of optical fibers and optical fiber sensors in radiation related measurements [2],

38

Radiation Effects in Materials

by referring to radiation effects in optical materials and some photonic devices. According to
this vision, the chapter is organized to cover the interaction of ionizing radiation with some
optical materials and optical fibers, followed by a reference to radiation effects on some photonic
devices based on optical fibers. The discussion addresses radiation effects produced by both
energetic photons and charged particles, as appropriate [3]. In this context, an overview of some
recently published results in the field is included, with a focus on original authors’ contributions.
The terrestrial radiation environments where optical and photonics components can be found
include, but are not limited to, high energy physics experiments, nuclear power plants [3],
fusion installations as the International Thermonuclear Experimental Reactor – ITER, or the
Laser Mégajoule – LMJ [4–8], high power laser installations [9], nuclear waste repositories [10],
high energy physics [11, 12], medical equipments for diagnostics or treatment [13]. On the
other side, applications of optical components or photonic devices can be found in spaceborne
instrumentation [14–16]. These environments involve various types of ionizing radiations,
depending on the application considered: X-rays or gamma rays, electron beams, alpha
particles, neutrons, protons, and Bremsstrahlung [3, 14, 17].

2. Radiation effects in optical materials
2.1. Optical materials
Extensive research was involved in the elucidation of defects formation in glasses, as investi‐
gations were performed in glasses with various compositions under ionizing and non-ionizing
radiation exposure. The studies were focused either on the materials degradation upon
irradiation or on the possible use of such materials in radiation dosimetry [18, 19]. The radiation
induced changes depend on the glass composition, total dose, dose rate, temperature and
humidity during exposure, and post irradiation heating of the sample [19]. The operation of a
glass-based dosimeter can be decided as function of radiation sensitivity, linearity of the
response, stability of the radiation produced effect, and possibility to re-use the material.
Besides glass-based optical materials, radiation hardening tests were performed on various
other optical materials. More than 20 years ago radiation induced defects were studied in
BaF2 crystals by exposing them to gamma rays (from 10 Gy to 47 kGy) and observing the optical
attenuation recovery (between 300 and 700 nm) under UV radiation and the scintillating signal
[20]. Samples from different manufacturers exhibited radiation induced attenuation (RIA)
saturation starting from 102 Gy. Crystal impurities and defects are the primary source of the
optical attenuation increase in the 190–250 nm and 500–600 nm spectral bands induced by
gamma rays [21]. BaF2 and LaF3 were subjected to Ne and U ions (at energies from 1.4 to 13.3
MeV/u) bombardment, and their degradation was investigated by scanning force microscopy
(SFM), optical spectroscopy and surface profilometry. RIA for BaF2 shown an increase at λ =
240, 420, 550 and 750 nm, while LiF3 crystals remained almost unchanged spectrally. Surface
topography studies indicated the presence of hillock in the irradiated zone [22].
Neutron irradiation was done on Y3Al5O12, CaF2 and LiF and RIA was monitored for UV-visible
spectra. For Y3Al5O12 samples an increase of the optical attenuation was present for wavelength

Radiation Effects in Optical Materials and Photonic Devices
http://dx.doi.org/10.5772/62547

lower than 350–400 nm. CaF2 and LiF single crystals degrade their optical transmission after
neutron exposure mostly in the 400–500 nm region. When heated after the irradiation RIA for
the three crystals recovers according to different patterns [23].
Gamma irradiation (dose rate 110 Gy/h, total doses of 500 Gy, 2 kGy, 8 kGy, 20 kGy) was
conducted on CaF2, Fused Silica and Clearceram in order to evaluate their qualificat