Abstract
Polarised luminescence spectra of Cr3+-doped beta -alumina crystals were taken at temperatures between 78 and 295K. From luminescence excitation spectra the energy level scheme of the Cr3+ ion is obtained. This turns out to be very similar to that of ruby, with the Cr3+ ion substitutional for the Al3+ ion in the octahedral sites of the spinel block structure in beta -alumina. Time-resolved spectroscopy allows for the separation of the contributions from non-equivalent centres, characterised by lifetimes ranging from 0.7 ms to 50 ms. Three different sets of centres were identified, corresponding to Cr3+ ions in centrosymmetric and noncentrosymmetric sites. The partially disordered structure of the host crystal is reflected in the shape of the emission lines, whose characteristics are intermediate between those typical of ordered compounds and amorphous ones.
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