Optical behaviour of sodium β-aluminogallate single crystals doped with Cr3+and Cr3+–Nd3+

Abstract

Single crystals of formula Na1.6(Al0.5–xGa0.5Crx)11O17.3(x= 0.002, 0.01), were grown by the flux evaporation method. The crystal structure study shows a β-alumina type structure with strong delocalisation of Na+ ions and an inhomogeneous distribution of Ga3+. In addition to a broad and intense emission band, corresponding to the Cr(4T2→4A2) transition, the fluorescence spectra present two other signals attributed to the Cr(2E→4A2) transition of various chromium species. At 700 nm, the emission band corresponds to a D3d symmetry site and at 709 nm to a CMs symmetry site occupancy. Cr3+ pairs are also identified. Time-resolved fluorescence spectroscopy and lifetime measurements are used to determine the Cr3+ site occupancy and to study Cr3+–Cr3+ interactions.