Optical and microwave spectra of Cr³⁺ in the spinel ZnGa ₂O₄

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 4A2 and lower 4A terms show a trigonal field splitting of <500 and 1500 cm-1 respectively. The zero field splittings of the 4A2 level (1.048 cm -1) and 2E 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=18000 cm -1, 5 = 670 cm-1, C = 3230 cm-1, ζ = 250 cm-1, v= -650 cm-1, v′= -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.