QUENCHING OF THE FLUORESCENCE FROM CHROMIUM(III) IONS IN CHROMIUM-DOPED FORSTERITE BY AN ALUMINUM CODOPANT

The H2O2-assisted sol-gel method was used to synthesize polycrystallin e chromium and aluminum codoped forsterite powders with varying ratios of aluminum to chromium. These powders were used as feedstocks to gro w single crystals by the floating zone method. The dopant composition of the resulting pleochroic crystals was determined by neutron activat ion analysis, Hyperfine splittings observed in the EPR study revealed that over half of the Cr3+ ions were present as chromium-aluminum pair s. The near-IR emission spectra of the crystals displayed the high rat ios of Cr4+ to Cr3+ fluorescence intensities that have been previously reported for co-doped forsterite. Integration of the Cr4+ and Cr3+ EP R resonances, however, revealed that most of the chromium was in the 3 + oxidation state. The high ratio of Cr4+/Cr3+ emissions is attributed to quenching of the fluorescence from Cr3+.