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We investigated photo-induced effects in Ge-Ga-Se films. It was found that, thermal annealing causes the increase of the bandgap in the as-prepared films, and all three annealed films show photodarkening (PD) behavior with light illumination but the change of optical bandgap is minimum in Ge25 film. Such PD behavior can be recovered by reannealing of the film. The kinetic process of Tf/Ti exhibits part recovering of PD during the cycle of laser on and off. Moreover, no obvious structural change can be observed in the Raman spectra of the films at different states, especially in that of Ge25 film. [ABSTRACT FROM AUTHOR]

We presented an experimental comparison of the core-composition difference on the suppression of the photodarkening and transverse mode instability effects. Two core-composition fibers, entailing Yb/Al/Ce and Yb/Al/P co-doped fibers, were fabricated by MCVD process combined with solution doping technique. The parameters of two fibers were almost the same. The PD-induced loss at equilibrium was 3.94 dB/m at 702 nm in Yb/Al/Ce fiber, while it was 0.99 dB/m in Yb/Al/P fiber. To obtain a deeper understanding of the impact of PD on laser performance, a bidirectional pumping fiber amplifier was constructed. Compared with Yb/Al/Ce co-doped fiber, the TMI thresholds of Yb/Al/P co-doped fiber were enhanced in co-pumped and counter-pumped schemes. Meanwhile, the slope efficiency in bidirectional scheme was promoted by 4%. Moreover, the transmittance at 638 nm confirmed the superior PD resistance of Yb/Al/P co-doped fiber. These experimental results pave the way for the further development of high-power fiber lasers.

To get insights into glassy Se at Kauzmann temperature, Se clusters including helical and disordered H–nSe–H chains with n ≤ 20 are constructed, using an ab initio molecular orbital package. The study demonstrates the existence of kinked chains with bistable dihedral‐angular conformations, which have similar total energies to that in straight helical chains. Electronically, such kinked chains possess wider optical gaps with no gap states, which is less efficient in localized electronic excitation. This would predict that the photodarkening cannot appear in fully stabilized glasses at Kauzmann temperatures, the behavior being similar to that demonstrated for liquid Se lying in thermal equilibrium. [ABSTRACT FROM AUTHOR]

In this paper, an improved mathematical model is proposed by taking the factors of high-energy photons and temperature into consideration, which is verified and explained by the experimental data in our experiments and other papers. By fitting and analyzing the experimental data, we can quantitatively determine the relationship between the pump power P λ and the photon frequency ν in the fiber core, the core area A and the temperature T of the fiber core and PD loss, and explain the mechanism of the PD phenomenon to a certain extent. We believe that the excitation of color centers by high-energy photons is the main reason for photodarkening. Furthermore, there is a positive correlation between the power of high-energy photons and the photodarkening rate, and the temperature is positively correlated with the saturated photodarkening absorption. [ABSTRACT FROM AUTHOR]

In this work, we revealed the possible mechanisms of the photodarkening in Pr3+ ions singly doped and Pr3+/Ce3+ co‐doped silicate glasses and fibers induced by X‐ray and 488‐nm laser radiations and studied the role of Ce3+ in increasing radiation resistance in Pr3+‐doped silicate glasses and fibers. The absorption, emission, electron paramagnetic resonance (EPR), radiation induced attenuation spectra, and X‐ray photoelectron spectroscopy (XPS) of Pr3+ singly doped and Pr3+/Ce3+ co‐doped silicate glasses before and after X‐ray radiation were measured and analyzed. The fluorescence intensity and photoinduced attenuation of Pr3+ singly doped and Pr3+/Ce3+ co‐doped silicate fibers at visible wavelengths pumped by 488‐nm laser were measured and analyzed. The influence of Ce3+ ions co‐doping on the spectroscopic properties of Pr3+ ions as well as the radiation‐induced defects in silicate glasses was studied. Results demonstrate that both X‐ray and 488‐nm laser radiations will induce photodamage in Pr3+ ions‐doped silicate glasses and fibers. Co‐doping Ce3+ (by up to 1 mol%) is efficient to suppress the darkening induced by both X‐ray and 488‐nm laser radiations without influence on the luminescence behavior of Pr3+ ions in silicate glasses and fibers. Our studies demonstrate the promising potential of Pr3+/Ce3+ co‐doped silicate glasses for visible lasing applications. [ABSTRACT FROM AUTHOR]

Amorphous chalcogenide glasses are intrinsically metastable, highly photosensitive, and therefore exhibit numerous light-induced effects upon bandgap and sub-bandgap illumination. Depending on the pulse duration of the excitation laser, ChGs exhibit a series of light-induced effects spanning over femtosecond to seconds time domain. For continuous wave (CW) illumination, the effects are dominantly metastable in terms of photodarkening (PD) and photobleaching (PB) that take place via homopolar to heteropolar bond conversion. On the other hand, under nanosecond and ultrafast pulsed illumination, ChGs exhibit transient absorption (TA) that is instigated from the transient bonding rearrangements through self-trapped exciton recombination. In the first part of the review, we pay special attention to continuous wave light-induced PD and PB, while in the second part we will focus on the TA and controlling such effects via internal and external parameters, e.g., chemical composition, temperature, sample history, etc.

We report on a single-frequency fiber master oscillator power amplifier utilizing a polarization-maintaining step-index fiber with an Al/Ce/F core-glass composition doped with a very high Yb concentration (0.25 at.%). This design made it possible to use a very short fiber (~1 m) and to coil it in a tight radius (4 cm in the amplifier, while 2 cm gave similarly negligible bending loss) so that the packaged system is one of the most compact reported to date (~0.6 L). The use of a short fiber increased the threshold for stimulated Brillouin scattering well above 100 W while maintaining near-ideal beam quality. The fiber was pumped with a diode-pumped solid-state laser and cooled passively by spooling it on a grooved aluminum mandrel. The amplifier produced a strongly linearly polarized output at 1064 nm in the fundamental mode (M2 ≤ 1.2) with a 150 kHz linewidth and a power of 81.5 W for 107 W of launched pump power. No deleterious effects from the elevated thermal load were observed. The residual photodarkening loss resulting from the high Yb concentration, found to be small (~0.7 dB/m inferred at 1064 nm) with accelerated aging, reduced the output power by only ~20% after 150 h of operation. [ABSTRACT FROM AUTHOR]

Many studies have been conducted on the photodarkening in chalcogenide glasses, and a maximal change is demonstrated to appear around Ge20As25S55. However, the reason for this selected composition remains unanswered, for which a plausible idea is proposed here. It seems that the composition has a maximal atomic volume in the ternary system, which probably gives rise to least photoexpansion (or photocontraction). The idea suggests that disordered, moderately‐rigid networks are effective in enhancing the photodarkening through suppressing macroscopic viscous relaxation. [ABSTRACT FROM AUTHOR]

In this paper, an improved mathematical model is proposed by taking the factors of high-energy photons and temperature into consideration, which is verified and explained by the experimental data in our experiments and other papers. By fitting and analyzing the experimental data, we can quantitatively determine the relationship between the pump power Pλ and the photon frequency ν in the fiber core, the core area A and the temperature T of the fiber core and PD loss, and explain the mechanism of the PD phenomenon to a certain extent. We believe that the excitation of color centers by high-energy photons is the main reason for photodarkening. Furthermore, there is a positive correlation between the power of high-energy photons and the photodarkening rate, and the temperature is positively correlated with the saturated photodarkening absorption.

Yttrium oxyhydride (YHO) is a rare‐earth‐metal oxyhydride that has attracted considerable attention due to its outstanding photochromic properties. The transparency of YHO thin films across the infrared and visible spectral regions is reduced considerably under UV illumination (photodarkening) and recovers when the illumination is removed (bleaching). Although oxygen diffusion has been shown to be necessary for these processes, the exact mechanism for the photochromic behavior is not yet understood. In this work, infrared spectroscopy is utilized to investigate the effect of temperature on the photochromic properties of YHO thin films. The measurements show that YHO can photodarken at temperatures as low as 5 K, where anion diffusion is expected to be severely limited. The bleaching of the films is small, but not zero, for temperatures between 5 and 50 K. A stepwise recovery of the transmittance is observed as the temperature of the films is increased above 100 K up to 250 K. The temperature‐dependent data show that anion diffusion is not required to explain the photochromic behavior of YHO, and that an additional mechanism (or mechanisms), e.g., electronic charge transfer, contributes to the photochromic behavior of YHO, as well as other rare‐earth‐metal oxyhydrides. [ABSTRACT FROM AUTHOR]

We report on a single-frequency fiber master oscillator power amplifier utilizing a polarization-maintaining step-index fiber with an Al/Ce/F core-glass composition doped with a very high Yb concentration (0.25 at.%). This design made it possible to use a very short fiber (~1 m) and to coil it in a tight radius (4 cm in the amplifier, while 2 cm gave similarly negligible bending loss) so that the packaged system is one of the most compact reported to date (~0.6 L). The use of a short fiber increased the threshold for stimulated Brillouin scattering well above 100 W while maintaining near-ideal beam quality. The fiber was pumped with a diode-pumped solid-state laser and cooled passively by spooling it on a grooved aluminum mandrel. The amplifier produced a strongly linearly polarized output at 1064 nm in the fundamental mode (M2 ≤ 1.2) with a 150 kHz linewidth and a power of 81.5 W for 107 W of launched pump power. No deleterious effects from the elevated thermal load were observed. The residual photodarkening loss resulting from the high Yb concentration, found to be small (~0.7 dB/m inferred at 1064 nm) with accelerated aging, reduced the output power by only ~20% after 150 h of operation.

This study reports the radical elimination of the photodarkening (PD)-effect in Yb-doped fiber through deuterium loading. With deuterium pre-loading, no PD-induced excess loss of the Yb-doped fiber was observed under 915-nm pumping conditions. Moreover, the existing loss induced by the PD effect was also eliminated via deuterium loading, and the excess loss declined to nearly 0  dB/m. The method was also validated in a KW-level fiber laser experimental setup. In the 20/400-μm deuterium pre-loaded Yb-doped fiber, an output laser power of 1630 W and beam quality factor (M2) of 1.69 were obtained. The two parameters remained stable during the entire continuous operation process of 40 min, and displayed very little power fluctuation of <0.5%. The results of our experiments confirmed that deuterium loading can protect Yb-doped fibers from the PD effect, thereby improving the power and mode stability, which is often deteriorated by PD. Notably, the results of this study are beneficial in terms of further development of high-power fiber lasers. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) properties of PbSe and Sr2+‐doped PbSe quantum dots (QDs) doped in silicate glasses were investigated by changing the excited laser wavelength and intensity. When BaO was replaced by SrO, the Sr2+‐doped PbSe QDs formed and showed large blue‐shifts in both absorption and PL bands compared to the PbSe QDs. It is attributed to the increasing in band gap resulted by the incorporation of Sr2+ ions into PbSe QDs. These two kinds of QDs were excited by the laser with the wavelengths of 1319 and 1532 nm. When rising the pumping intensity up to 1000 mW, the PL intensity from Sr2+‐doped PbSe QDs monotonically increased, while, the PL intensity from PbSe QDs reached maximum at pumping intensity at ~200 mW (λex = 1319 nm) and ~300 mW (λex = 1532 nm). The good resistance to photodarkening of Sr2+‐doped PbSe QDs is indicated passivation effect on the surface defects from Sr2+ ions doping. For Sr2+‐doped PbSe QDs the anti‐Stokes photoluminescence (ASPL) were observed when using both 1319 and 1532 nm excitation. The integrated intensity of the ASPL is linear with the excitation intensity, which indicates that the ASPL belongs to the phonon‐assisted one‐photon process. And the ASPL intensity as a function of excitation intensity shows a size dependence of the QDs. [ABSTRACT FROM AUTHOR]

We report on our investigation of photo-darkening (PD)-induced thermal load in Yb-doped fiber lasers and the effective suppression by H2-loading. Compared with a quantum defect, the contribution of heat produced by PD was evaluated, indicating PD may become the primary heat source. To reduce the heat generation, the effect of H2-loading on thermal load was quantitatively analyzed. The experimental results showed that 86% of PD loss was mitigated and 82% of PD-induced thermal load was eliminated by H2-loading. In contrast, due to the presence of extra heat source, only 14% heat decreased in the Ce-doped fiber at similar PD loss level. The results indicate that H2-loading is promising for further improving the stable operation of fiber lasers. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Study of the fluorescence properties of MAPI perovskite in air and nitrogen. • Changes in fluorescence are correlated with morphology changes through XRD. • Evidence that degradation occurs at the same time as photobrightening. • Highlights the complex nature of fluorescence behaviour of perovskite thin-films. Abstract Organic-inorganic perovskite materials, such as methylammonium lead iodide, are good candidates for the next generation of solar cells with an impressive certified 23.7% power conversion efficiency. However, their development is impeded by their poor stability to oxygen, moisture, light and combinations of these. The bulk photoluminescence of perovskite films is extremely sensitive to the environment (humidity, light intensity, temperature, atmosphere) and has been shown to undergo rapid photobrightening and photodarkening. Here, we study the changes in photoluminescence behaviour (intensity, wavelength and full-width-at-half-maximum) in both air and nitrogen and correlate this with changes in the crystal structure of the films under illumination. We show that photodarkening is caused by degradation of the perovskite and that both brightening and some degree of darkening are competitive processes occurring simultaneously. During photobrightening the fluorescence emission spectrum red-shifts which can be explained by the halide redistribution and passivation of trap states in the perovskite. We conclude that care is required when measuring fluorescence of perovskite due to the important variations in intensity, emission wavelength and full-width-at-half-maximum. [ABSTRACT FROM AUTHOR]

Abstract Yb3+, Yb3+/Al3+, Yb3+/P5+, and Yb3+/Al3+/P5+ doped silica glasses were prepared via the sol-gel method combined with high-temperature sintering. The amorphous nature of as-prepared glasses was confirmed by the X-ray diffraction analysis. The composition dependent ultraviolet (UV) absorption changes in the glasses were correlated with the local structure of Yb3+ ions that was obtained by pulsed electron paramagnetic resonance (EPR). In situ photoluminescence evolution and continuous wave EPR spectrum of color centers induced by a 193-nm UV laser were recorded, and the role of UV absorption bands in the photodarkening process was discussed. The results indicated that the strong UV absorption bands in the range of 190–290 nm were primarily attributed to the charge-transfer (CT) transition from O2– to Yb3+ and the position of CT bands shifted to a higher energy level with increases in the electronegativity of next nearest neighbor atoms (Al/Si/P) of Yb3+ ions. Furthermore, the results revealed that excitation into the CT bands leads to the generation of oxygen hole centers and Yb2+ ions. The study is useful for understanding the underlying mechanism of photodarkening in Yb3+-doped high-power laser fibers. Highlights • High-purified, large-size and homogeneous doping glass samples were prepared using sol-gel method combined with high-temperature sintering, which ensures the accuracy and convenience of subsequent structural and property testing. • Effect of Al and/or P doping on the local structure of Yb3+ ions and UV absorption spectra of doping glasses was systematically studied, and the relationship between them was revealed for the first time. • The nature of UV-radiation induced color center is identified by in-situ photoluminescence and continuous wave EPR spectra, and the role of UV absorption bands in the process of photodarkening was discussed. [ABSTRACT FROM AUTHOR]

Abstract To investigate the laser performance and material characters of Ce/Yb/F-codoped aluminosilicate binary glass fiber, we took commercial Nufern-20/400–9 M fiber as a research object. 1.83 kW laser output power at 1066 nm with an optical-to-optical efficiency of 81.7% was achieved in master oscillator power amplifier (MOPA) system. No power roll-over was found for about 1 h at the maximum power, indicating Nufern-20/400-9M fiber has excellent power stability. Ce3+ ions can effectively suppress the regular photodarkening phenomenon easily-observed in Yb-doped aluminosilicate glass fiber. However, as the laser output power exceeded 1 kW, optical nonlinearities, such as four-wave-mixing and stimulated Raman scattering, emerged and the beam quality factor M 2 degraded heavily from 1.60 for 1 kW to 2.37 for 1.8 kW. The studying results show that Nufern-20/400-9M fiber with strong nonlinearities and low threshold of modal degradation in the MOPA system which is suitable for kW-level fiber laser applications. [ABSTRACT FROM AUTHOR]

Abstract 5 at.% Yb:Y 2 O 3 transparent ceramics were fabricated using vacuum sintering plus HIP. The ceramics doped with 1 at.% ZrO 2 as the sintering additive were densified at 1700 °C in vacuum followed by HIPing at 1775 °C, while those without sintering additives were densified at 1520 °C in vacuum followed by HIPing at 1450 °C. After sintering, both ceramics had relatively high in-line transmittance. However, during laser experiments, the ZrO 2 -doped Yb:Y 2 O 3 (Zr-YbY) ceramics were photodarkened when irradiated by 940 nm pump light. The discoloration might be attributed to the formation of Zr3+ color centers during lasing. In contrast, no photodarkening effect was detected in the pure Yb:Y 2 O 3 ceramics without sintering additives (P-YbY). The P-YbY ceramics exhibited much higher lasing efficiency (17%) than the Zr-YbY ceramics (9%). To our best knowledge, it is the first time that the photodarkening effect was detected in rare-earth doped sesquioxide laser ceramics. [ABSTRACT FROM AUTHOR]

• Study of mechanisms of the photodarkening in chalcogenide glasses. • Ab initio molecular orbital calculations for S/Se chains. • Defect models are less plausible. • Strains in intermolecular distances cause the photodarkening. • The phenomenon is connected with the glass transition. The photodarkening is observed in many chalcogenide glasses, while its mechanism remains controversial. There are few reports which discuss the whole process. We consider the mechanism through ab initio molecular-orbital calculations for the simplest systems, elemental S and Se clusters. The results manifest that valence-alternation pair (VAP) defects are unstable in the dark, thus it cannot be an origin. On the other hand, intimate VAPs can be quasi-stable, while those affect only band-edge states, which is contradictory with observed spectral modifications. By contrast, strains in van-der-Waals (VDW) distances are likely to broaden the lone-pair electron band. A refined bond-twisting model is able to trace such a process, including annealing stage. Quantitatively, the maximal red-shift of ∼0.1 eV can be related with quasi-stable strains containable in a medium-range volume of ∼1 nm3, which can be thermally released through atomic twisting motions over angular barriers with a height of ∼1 eV. [ABSTRACT FROM AUTHOR]

We describe a framework for modeling the writing and erasure of thermally-distributed activated processes that we can specifically apply to UV-induced refractive index change, particularly in fibers. From experimental measurements (isochrons and/or isotherms), this framework allows to find the distribution function of the activation energy by providing only a constant, which can be determined by a simple variable change when a few assumptions are fulfilled. From this modeling, it is possible to know the complete evolution in time of the system. It is also possible to determine the annealing conditions for extending a lifetime. This approach can also be used for other physical quantities, such as photodarkening, stress relaxation, and luminescence decay, provided that it can be described by a distribution function.

The aim of this work is to experimentally investigate one-dimensional (1D) photonic crystals (PCs) and the photo-induced effect of their defect layer. A radio frequency (RF) magnetron sputtering technique was used to fabricate ten-pair 1D PCs with and without a single defect layer, utilizing TeO 2.33 and SiO 2 with different refractive indices. The photonic band structures in the PCs were also analyzed, and the measured transmittance (T) spectra were compared with the simulated results. The 1D PC without a defect layer had a forbidden band gap in the wavelength range of 1203–1421 nm. The 1D PC with defect layer generated a sharp peak within a photonic band gap (PBG) at the central wavelength of 1291 nm. After exposure to a He-Cd laser of λ = 325 nm, the resonant T peak shows red-shift because of photodarkening effect caused by the behavior of valence-alternation pairs (VAPs) in amorphous chalcogenides. [ABSTRACT FROM AUTHOR]

Photodarkening in Yb-doped fibers is known to be dependent of Yb population inversion. In addition to this dependence, we report that pump wavelength selection plays a significant role in photodarkening dynamics. It is found that 976 nm pump source can lead to more severe photodarkening effects than 916 nm pumping at the same inversion levels. This observation is consistent in Yb-doped fibers with various compositions. Our work reveals pump wavelength is another determinant factor of photodarkening besides the inversion level and emphasizes the importance of pump wavelength selection in high power Yb-doped fiber lasers and amplifiers. [ABSTRACT FROM PUBLISHER]

Multielement (ME) (P-Yb-Zr-Ce-Al-Ca) nanophase separated silica-glass-based optical fiber is fabricated through a conventional-modified chemical vapor deposition (MCVD) process, coupled with solution doping technique. The lasing and photodarkening behaviors of this ME fiber have been demonstrated and compared, in terms of its photodarkening (PD) performance at moderate pump powers (tens of Watts), with standard Yb-doped fiber with phospho-alumino-silicate (PAS) glass composition, which clearly reveals that the ME-Yb doped fiber is a promising candidate for laser applications with enhanced PD resistivity. [ABSTRACT FROM AUTHOR]

The laser irradiation on films brings many changes in its different properties for optoelectronic applications. The current work deals with the deposition of Sb 10 S 15 In 15 Se 60 film by thermal evaporation technique and then laser irradiated at different time durations to study the variation in structural and optical properties. In the present investigation, laser irradiation was carried out by 532 nm laser (2.33 eV) for different time durations, such as 0, 10, 20, 30, and 60 min. Due to the irradiation process, the surface morphology changed while the structure remained polycrystalline in nature by increase in crystallinity with irradiation time. All the optical parameters (linear and nonlinear) were calculated from UV–Vis spectroscopy data. Due to irradiation, the transmission decreased and shift in absorption edge occurred that leads to the reduction in optical gap from 1.73 eV to 1.27 eV. Such photodarkening phenomenon increased the refractive index which led to the increase in nonlinear optical entities like nonlinear refractive index and 3rd order nonlinear susceptibility. The variation of carrier concentration, VELF, and SELF, were also evaluated at different exposure times. The observed changes in the structural and optical properties with laser irradiation are suitable for various photonics devices. The laser irradiation on the surface of Sb 10 S 15 In 15 Se 60 thin film increased the crystallinity and decreases the transmission as well the optical bandgap, and consequently increased refractive index. The nonlinear absorption coefficient decreased with irradiation time. [Display omitted] [ABSTRACT FROM AUTHOR]

The photodarkening phenomenon in alumino-silicate glass preforms, doped with different ytterbium concentrations, was studied. The UV band, comprised between 180 and 350 nm, was examined before and after irradiation at 976 nm. The non-linear dependence of 240 nm band with concentration after infra-red irradiation was demonstrated and ascribed predominantly to Yb3+ pair’s interaction. The emission spectrum after the excitation in UV spectral region showed increased intensity after photodarkening, probably due to Yb2+ ions creation. Phenomenological photodarkening model and the possible existence of several defect types are presented.

Interaction of intense ultrashort laser pulses with wide bandgap materials is dominated by nonlinear absorption that can be measured by monitoring the transmission of incident pulse or a weak probe pulse. Transmission of incident pulses focused inside glass exhibit a gradual decline after nonlinear absorption sets in at a certain threshold laser fluence. In contrast, we demonstrate a step-function like self-limiting behaviour in transmission of incident pulses inside polymers, dropping abruptly to ∼ 20% (∼ 35%) in PDMS (PMMA) and remaining nearly constant beyond the threshold fluence. The self-limiting threshold, which decreases with the number of incident pulses, is also associated with the onset of blackening in polymers. By measuring the transmission of a probe pulse we show that the degree of blackening increases with the number of pump laser pulses reaching a saturation where only ∼ 40% of the probe is transmitted. Spectroscopic characterization of laser irradiated polymers indicates a localized reduction in the band gap when compared with pristine polymers. We exploit laser-induced blackening to fabricate embedded micro-optical white light filters by varying the laser fluence and the number of modified layers. [ABSTRACT FROM AUTHOR]

The influence of both thermal treatment and laser irradiation on the structural and optical properties of films in the Sb 2 O 3 –Sb 2 S 3 system was investigated. The films were prepared by RF-sputtering using glass compositions as raw materials. Irreversible photodarkening effect was observed after exposure the films to a 458 nm solid state laser. It is shown, for the first time, the use of holographic technique to measure “in situ”, simultaneously and independently, the phase and amplitude modulations in glassy films. The films were also photo-crystallized and analysed “in situ” using a laser coupled to a micro-Raman equipment. Results showed that Sb 2 S 3 crystalline phase was obtained after irradiation. The effect of thermal annealing on the structure of the films was carried out. Different from the result obtained by irradiation, thermal annealing induces the crystallization of the Sb 2 O 3 phase. Photo and thermal induced effects on films were studied using UV–Vis and Raman spectroscopy, atomic force microscopy (AFM), thermal analysis (DSC), X-ray diffraction, scanning electron microscopy (MEV) and energy-dispersive X-ray spectroscopy (EDX). [ABSTRACT FROM AUTHOR]