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

Chromium-doped nano-glass-ceramic samples containing crystallites of alpha- and gamma-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 degrees C during 2 h) up to tens of microns (additional heat treatment at 900 degrees 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 alpha-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 T-3(2) (Cr4+) state is similar to 12 mu s at 300 K and 65-70 mu s 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 mu s at room temperature and 7-9 mu s at 77K) was observed in the samples in which gamma-LiGaSiO4:Cr4+ crystallites were present. The origin of this fluorescence is so far unclear. (C) 2010 Elsevier B.V. All rights reserved.