Determination of exchange parameters of Cr3+ pairs in MgAl2O4 by optical measurements

The emission and luminescence excitation spectra of nearest-neighbor Cr3+ pairs in spinel MgAl2O4 have been studied. Analyses of these spectra yield the (4A2, 4A2) ground state level splittings. They are described by −JS̄1⋅S̄2+j (S̄1⋅S̄2)2, with S1=S2=3/2, J=−(29±3) cm−1, and j=−(3±2) cm−1. A couple of transitions to the first excited pair state (4A2, 2E) have been observed in the excitation spectrum; however, the data are insufficient to determine the parameters describing the exchange splittings of the excited state.