Optical and Microwave Spectra of Cr3+ in the Spinel ZnGa2O4

Abstract

The EPR, optical absorption, and fluorescence spectra of Cr3+ in the spinel ZnGa2O4 have been measured and interpreted using a crystal-field model. The EPR experiments can be described by a spin Hamiltonian whose parameters are: 2D = + 1.048 ± 0.001 cm−1, g‖ = 1.9774 ± 0.0005, g⊥ = 1.9761 ± 0.0005. The broad band transitions to the T24 and lower T14 terms show a trigonal field splitting of < 500 and 1500 cm−1 respectively. The zero field splittings of the A24 level (1.048 cm−1) and E2 level (40.0 cm−1) are considerably different than in the two other spinel systems which have been reported, i.e., ZnAl2O4 and MgAl2O4. The model parameters used in the numerical calculations are: Δ = 18 000 cm−1, B = 670 cm−1, C = 3230 cm−1, ζ = 250 cm−1, υ = − 650 cm−1, υ′ = − 1100 cm−1, k = 0.7. The detailed structure of the phonon sidebands and fluorescence, which is tentatively assigned to exchange-coupled Cr3+ pairs, are significantly different from other spinels.