UV Laser Decay of Oxygen‐Deficient Centers in Silica Glasses

Abstract

Oxygen-deficient centers decay with simultaneous formation of color centers in IR and UV grade silica glasses under KrF laser irradiation was studied. The nonexponential dependence of the ODC photodecay in silica glass on the UV irradiation dose (number of laser pulses) was observed. Postpulse long-time temporal behaviour of recombination luminescence and laser induced photoconductivity was analyzed for the two types of glasses in time scale up to 0.5 ms. Long time fluorescence tail is attributed to migration of electrons through the shallow traps before recombination and recovery of ODC. The models of postpulse recombination which can explain the observed nonexponential behaviour of ODC decay (geminal and homogeneous) are discussed. The principle part of impurities caused electron traps in the postpulse ODC recombination is shown.

Photoinduced Reactions of Oxygen-Deficient Centers with Molecular Hydrogen in Silica Glasses

“…The increase of light intensity results in an increase of the possibility of multistep processes and subsequent photoionization of ODC5•6 ODC + 2 hv -E' center + e (20) The possibility of this pathway of ODC photoreaction was shown by ESR and UV spectroscopic detection of laser-induced E' centers, by the quadratic dependence of photoreaction yield on laser pulse fluence, and also by direct measurement of photoconductivity in oxygen-deficient silica glasses. 6 In our experiments, the UV pulse energy fluence was ionization of ODC must also be high.6 Figures 6b,c and 7b demonstrate our experimental results on UV laser photochemistry of ODC in hydrogen-saturated silica fibers. The bleaching of the 248 nm ODC absorption band is several times stronger than that for low-intensity irradiation (mercury lamp) with the same dose.…”

“…The electronic photoexcitation of these ODC gives a strong photoluminescence with maxima at 280-285 nm (singlet-singlet transition) and 450-455 nm (triplet-singlet transition).1 These defect centers can be stabilized both in the bulk and on the surface of silica glasses.2 Irradiation of ODC with UV light initiates reactions which lead to the formation of new types of defects. [3][4][5][6] In previous works,5-8 some important features of these processes stimulated by UV light (both laser and conventional) with different intensities have been shown. The various chemical processes may be used to modify the defect structure of glasses and, thus, to obtain new optical properties.…”

“…The Scheme of ODC Photoreactions. Equations[2][3][4][5][6][7] describe the photoexcitation of ODC and the following reactions of singlet and triplet states with molecular hydrogen (ODC) + hv -(ODC)s, (photoexcitation) (W0) (2+ hv (triplet luminescence) (fcj. )(6) (ODC)T, + H2 products (quenching of trip lum) (ZR T) '…”

“…Figure6. Absorption spectra of KUVI-grade fiber samples before UV irradiation (curves 1), after UV irradiation (curves 2), and after postirradiation annealing at 500 K (curves 3): (a) mercury lamp irradiated fiber samples.1 = 5 mW/cm2, t = 15 min, T = 295 K. (b) KrF laser-irradiated fiber samples.…”

Changes in the Raman and Fluorescence Spectroscopic Signatures of Irradiated Organic‐Mineral Mixtures: Implications for Molecular Biosignature Detection on Mars

“…To confirm that the observed fluorescence is organic, a subset of the fused silica samples was exposed to repeated laser pulses with the deep ultraviolet (DUV) laser (248.6 nm). Previous work found that exposing fused silica to repeated laser pulses of varying energies can either anneal crystal defects resulting in a decrease of the ∼280 nm feature intensity or increase the concentration of defects, thus increasing the 280 nm feature intensity, depending on laser energy and/or thermal environment (Bagratashvili et al., 1992; Leung et al., 1991; Morgan et al., 2022; Zhou et al., 2014). In this work, repeated laser pulses of several fused silica samples resulted in a decrease of all fluorescence, including the 280/295 nm feature (Figure 4).…”