Photoinduced conversion of optically active defects in germanium-doped silica

Identification of Sn variants of theE′center in Sn-dopedSiO2

“…Few works on silica-based optical fibers analyzed the EPR features of EЈ-like Ge centers 8 and their behavior during photoactivated processes. [9][10][11][12][13] Other promising substitutionals, particularly Sn, 14,15 could be embedded in silica but their substitutional role is more questionable. 16,17 To our knowledge, no direct EPR evidence of EЈ-Sn centers has been reported.…”

Anisotropic luminescence photo-excitation in H2-loaded Ge-doped silica exposed to polarized 193nm laser light

“…[5,6,15]. This feature has been attributed by some authors to the coexistence of structurally different defect types and by others that attributes to a single defect affected by the structural environment inhomogeneity arising from the amorphous matrix [9,14,16].…”

“…The UV-induced bleaching of this band leads to the formation of new absorption bands at %4.6 eV, %5.8 eV and %6.2 eV and may also give rise to luminescence [2][3][4][5][6][7]. In particular, fiber irradiated with UV light at 5 eV displays an emission of broadband blue fluorescence around 285 nm (4.4 eV) and 400 nm (3.1 eV), referred to as a and b bands, respectively [2].…”

“…Several works propose that the defects involved both in absorption and fluorescence are the same [3,4] at least for low Gecontent SiO 2 . However, attempts to correlate the photo-luminescence (PL) to the UV absorption spectra as a function of UV-exposure or heat treatments have lead to opposite conclusions [5,6] in 'highly' (>1 wt%) Ge-doped glasses. This leads to think that luminescence center is not the main one but it can absorb anyway or 'receive' energy through a transfer.…”

Nucleation-controlled vacancy formation in light-emitting wide-band-gap oxide nanocrystals in glass

“…31 In Ge-containing silica-based glass, light emission in the violet spectral region is mainly expected from oxygen deficient defects consisting in twofold coordinated O-Ge-O sites. [31][32][33] However, in such defects, the emission is ascribed to triplet-to-singlet transitions with a decay time of 0.1 ms, 32 incompatible with the observed fast decay in the ns domain. Instead, violet luminescence with few ns of lifetime is typical of alkali-germanates and alkali-silicates, 34,35 arising from non-bridging groups 3ORT-O-M with T = Si, Ge and M = Li, Na.…”