The fluorescence of Cr3+ in ordered and disordered LiAl5O8 and in LiGa5O8

The spectra of Cr3+ in ordered and disordered LiAl5O8 and LiGa5O8 are fairly complex, consisting of a strong zero phonon line with weaker lines on both high and low energy sides of the main line. The origins of the most most prominent lines in LiAl5O8:Cr3+ are identified and it is show that a number of them are zero phonon lines, probably due to Cr3+ in sites having octahedral coordination with differing distortions, and that even in the ordered phase of this compound it has local domains characteristic of the disordered phase. It is also show that the previously reported R line splitting, with an abnormal value of 266 cm-1, consists in fact of two separate Cr3+ centers in LiAl5O8, compled through phonon-assisted energy transfer. The large R-line splitting observed in LiGa5O8:Cr3+, 278 cm-1 in magnitude, may also be due to the presence of two independent centers. (Author)