Structural changes induced by KrF excimer laser photons inH2-loaded Ge-dopedSiO2

Abstract

Photochemical reactions related to the Ge lone-pair center ͑GLPC͒ that are induced by KrF excimer laser photons in H 2 -loaded Ge-doped SiO 2 glass have been investigated. Without the H 2 loading, the Ge electron center ͑GEC͒ and the positively charged GLPC were induced by the laser irradiation. In the H 2 -loaded sample, the GEC, the Ge EЈ center, and the germyl radical ͑GR͒ were induced by the irradiation, while the positively charged GLPC was not observed after the irradiation. If the H 2 -loaded sample was thermally annealed after the photon irradiation, the concentration of the photo-induced GEC decreased monotonically with an increase in the annealing temperature. On the other hand, the concentration of the GR increased up to the annealing temperature of 160°C, and it decreased at higher temperatures. Without the pre-irradiation, the induction of the GR was not observed even in the H 2 -loaded sample. From these results, it is concluded that the positively charged GLPC is terminated with a hydrogen atom in the H 2 -loaded sample and then becomes the GR by trapping an electron thermally released from the GEC. ͓S0163-1829͑99͒05631-3͔ PHYSICAL REVIEW B 15 AUGUST 1999-I VOLUME 60, NUMBER 7 PRB 60 0163-1829/99/60͑7͒/4682͑6͒/$15.00 4682

Ultraviolet-light-induced processes in germanium-doped silica

“…The increased absorption below 242 nm may well be due to the absorption edge reached from the defect state D 1 , and 213 nm will then correspond to excitation to the top of the band gap. This is a considerably simpler and more straightforward interpretation than the assignments sometimes found in other papers 26 . UV-induced index changes at 193 nm may well proceed through interactions with these states.…”

“…If one measures the absorption spectrum of UV-irradiated silica glass with positive index changes, one finds some complicated changes in the absorption near 242 nm. 26 In addition there is a weak absorption near 435 nm and a very weak absorption near 600 nm. 27,28 The complicated changes in the absorption near 242 nm have been assigned to the combination of an absorption near 275 nm, another absorption centered at 213 nm, and a reduced absorption at 242 nm.…”

“…27,28 The complicated changes in the absorption near 242 nm have been assigned to the combination of an absorption near 275 nm, another absorption centered at 213 nm, and a reduced absorption at 242 nm. 26 Some papers make a more detailed distinction between different contributions. The increased absorption below 242 nm may well be due to the absorption edge reached from the defect state D 1 , and 213 nm will then correspond to excitation to the top of the band gap.…”

Bleaching of optical activity induced by UV laser exposure in natural silica

“…The absence of Ge(2) defects in our wet samples could be due to their annealing by reaction with hydrogen, whose concentration in form of O-H bonds is higher, by about an order of magnitude, than in dry silica. Hence, the so produced Ge(2)-H groups could become H(II) centers by trapping an electron [23]. This process may be a further contribution to the post irradiation growth of H(II) centers observed in our samples [11].…”

H(II) Centers in natural silica under repeated UV laser irradiations

“…In fact, it has been hypothesized that a contribution to photosensitivity arises from conversion processes of Ge-related defects, one of which is the transformation of the optically active twofold coordinated Ge (=Ge •• ) into the paramagnetic H(II) center (=Ge • -H) by trapping a H 0 atom [2,[4][5][6]:…”