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

Chromium-doped nano-glass–ceramic samples containing crystallites of α- and γ-polymorphous modifications of eucryptite-like LiGaSiO4 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 Cr3+ and Cr6+ ions were observed in the vitreous precursors, whereas the absorption of Cr4+ ions prevails in the samples after ceramming. The measured fluorescent properties of the glass–ceramics containing only α-LiGaSiO4:Cr4+ 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 3T2 (Cr4+) 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:LiGaSiO4 single crystals. One more Cr4+ 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-LiGaSiO4:Cr4+ crystallites were present. The origin of this fluorescence is so far unclear.