Luminescence in rare-earth-doped thiospinels

Narrow line optical absorption and emission spectra have been observed in Nd³⁺- and Er³⁺-doped In2S3, CdIn2S4, and ZnIn2S4. All three spectra show essentially the same structure, and this indicates that the rare-earth ions occupy the same type of environment in the three lattices. The sites most probably have octohedral symmetry, since electron spin resonance results show that the site for CdIn2S4is octohedral. Fluorescence has been observed from all the Er³⁺- levels almost up to the host lattice band-gap energy above the ions ground state, under both X-ray and ultraviolet excitation. This fluorescence shows the same dependance on rare-earth concentration, method of excitation, and intensity for all three doped host lattices, provided the emission frequency is well removed from the band-gap frequency. The temperature dependance of the fluorescence, however, increases as the emission frequency approaches the host lattice band-gap frequency, and this indicates that a relationship may exist between the extent of the temperature dependance and the magnitude of the band-gap frequency.