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.
These single crystals are doped by ionic exchange in molten salts, part of the sodium being replaced by Nd3+. Studies of the Cr3+ emission and Nd3+ excitation spectra indicate that efficient Cr3+→ND3+ energy transfer takes place in this material at 300 K. From the low-temperature Nd3+ decay profile, it is suggested that the transfer occurs mainly from the 4T2 Cr3+ state, and that Cr3+ pairs do not participate significantly in this transfer.
- This article is part of the themed collection: Computer Modelling Studies of Condensed Matter