Luminescence of Cr3+ ions in ordered and disordered LiAl5O8

The phosphorescence and excitation spectra of Cr3+ ions in the ordered and disordered phases of LiAl5O8 have been measured and interpreted. In both phases Cr3+ substitutes for Al3+. In the ordered phase the rhombic symmetry is responsible for a relatively large splitting of 2E(2G), 2T1(2G) and 2T2(2G) levels and the occurrence of an intense zero-phonon line in the broad 4A2 → 4T2 absorption band. In the disordered phase three different sites for the Cr3+ ions have been found. This can be explained in terms of different nearest-neighbor Li+ and Al3+ ion distributions.