Nano-glass–ceramics containing chromium-doped LiGaSiO4 crystalline phases

Abstract

Abstract Chromium-doped nano-glass–ceramic samples containing crystallites of α- and γ-polymorphous modifications of eucryptite-like LiGaSiO 4 were fabricated by devitrification of Cr–Li–Ga–Si–O glass of various compositions. Evaluated sizes of the crystallites in synthesized samples are from tens of nanometers (in the case of ceramming at 570–650 °C during 2 h) up to tens of microns (additional heat treatment at 900 °C during 5 min). Spectroscopic investigations (absorption and fluorescence spectra, fluorescence decay kinetics) of the prepared vitreous precursors and of the nano-glass–ceramic samples were performed. The absorption bands of Cr 3+ and Cr 6+ ions were observed in the vitreous precursors, whereas the absorption of Cr 4+ ions prevails in the samples after ceramming. The measured fluorescent properties of the glass–ceramics containing only α-LiGaSiO 4 :Cr 4+ crystallites are as follows: the fluorescence peak position is 1280 nm, the FWHM of the fluorescence band is 270 nm, the lifetime of the excited 3 T 2 (Cr 4+ ) state is ∼12 μs at 300 K and 65–70 μs at 77 K. These properties are similar to those of the earlier investigated Cr:LiGaSiO 4 single crystals. One more Cr 4+ fluorescent center with a shorter decay time (1–1.5 μs at room temperature and 7–9 μs at 77 K) was observed in the samples in which γ-LiGaSiO 4 :Cr 4+ crystallites were present. The origin of this fluorescence is so far unclear.