Luminescence spectra of pure and doped GaBo3 and LiGaO2

Abstract

The luminescences of GaBO₃ and LiGaO₂ are reported. The former has Ga^III in octahedral sites (calcite structure), the latter in tetrahedral sites (ordered wurtzite structure). The Ga^III co-ordination number has the same influence on the luminescence as in the case of oxo-d⁰ complexes: the lower the co-ordination number, the higher the energy of the first absorption band, the larger the Stokes shift, and the less mobile the excited state. The broad-band spectra with large Stokes shift indicate that the nature of the optical transition involved is complicated. Dopants in GaBO₃ are Eu^III and Cr^III. They are characterized by magnetic-dipole emission due to the inversion symmetry site in calcite. The Cr^III ion yields ²E emission at 4.2 K, in contrast to Cr^III in isomorphous ScBO₃ where it yields ⁴T₂ emission. The dopant in LiGaO₂ is Fe^III which yields an intense deep-red emission with pronounced vibrational structure.