INFRARED LUMINESCENCE OF IRON-DOPED SYNTHETIC FORSTERITE

Luminescence spectra of an iron-doped (0.2%) synthetic crystal of forsterite have been measured at low temperature (15 K). These show several zero-phonon lines at 813, 1025. 1093 and 1134 nm, all with phonon side bands. The emission at 1093 nm is due to chromium (Cr4+) and occurs also in both nominally pure crystals and chromium-doped samples. However, the 813 nm line is ascribed to Fe3+ ions, probably in tetrahedral (Si) sites, on the basis of the measured lifetime (15.5 + - 0.5 ms) and the analysis of excitation spectra. The 1025 and 1134 nm lines have measured lifetimes of 8.4 and 5.7(+ - 0.5) mus respectively at 20 K and are similar in other respects. It is suggested that these lines may be due to Fe2+ ions in octahedral (Mg) sites.