Effect of cooling on the optical properties and crystallization of UV-exposed photo-thermo-refractive glass

Quantitative UV–VIS spectroscopic studies of photo-thermo-refractive glasses. I. Intrinsic, bromine-related, and impurity-related UV absorption in photo-thermo-refractive glass matrices

“…3, the general patterns of the UV spectra of standard PTR glass (Spectrum 1) and bromine-containing PTR glass matrix sample (Spectrum 2) are, in general, similar to those presented in a few sources touching upon this topic [12,26,28,34]. In agreement with [28], the spectrum of standard PTR glass differs from that for the bromine-containing PTR glass matrix in the shift of a steep rise in the UV absorption to the lower wavenumbers and in the occurrence of an additional band around~32,800 cm -1 (305 nm) known [12,20,21,27,28] to be due to the 2 F 5/2 →5d 1 Laporte allowed optical transition of Ce 3+ ion. The only difference is the fact that Spectrum 2 is free of the Cr 6+ -related impurity band that occurred in the spectrum of bromine-containing matrix from [28].…”

“…It is these nano-sized NaF crystals that are considered to be responsible for a decrease in the refractive index of the treated PTR glass sample as a whole. In [26,27], a substantial role of bromine in these crystallization processes is stressed.…”

“…The main efforts of investigators were confined, until now (see, for example, [26][27][28][29][30], to analyzing the structure of a 400 to 500 nm envelope due to the plasmon resonance on metallic silver particles that dominates the spectra of completely treated samples (i.e., those subjected to both the UV irradiation and heat treatment). The UV spectral manifestations of dopant valence states responsible for the resultant formation of silver particles were, in most cases, outside the scope of these studies.…”

“…The longer wavelength 280-350 nm region of the spectra is known [12,20,21,27,28] to contain a broad band centered around~305 nm (32800 cm -1 ) that turns out to be (with the impurity bands neglected) the only one spectral feature observable distinctly in the raw experimental spectra of these glasses. This band, like the one in the spectra of other silicate glasses, is assigned in the above sources to the 4f 1 →5d 1 electronic transition in the Ce 3+ ion.…”

“…In the shorter wavelength 200-280 nm region, the UV spectra of initial PC/MC and PTR glass samples are known [12,20,21,27,28] to be characterized by a rapid smooth rise in the absorptivity with a decrease in wavelength that is considered to be due to the envelope of bands related to several activators in the valence states such as Ce(IV), Sb(III), Sb(V), and Ag + . The envelope center is estimated to be located around~245 nm, the short-wavelength wing of the envelope seeming to overlap greatly with the intrinsic absorption tail of glass matrix.…”