OPTICAL EMISSION SPECTRUM OF CR-3+-EU-3+ PAIRS IN EUROPIUM GALLIUM GARNET

Measurements of the emission spectrum of pure and chromium-doped europium gallium garnet are presented. The emission from weakly coupled Cr3+-Eu3+ pairs is of primary interest, and as was previously found for EuAlO3: Cr3+, fluorescence originates on the chromium Eg2 level and terminates on the FJ7 levels of neighboring europium ions. Pair transitions to J=3 through 6 have been observed. The energy levels of the final states are in good agreement with the FJ7 levels of the pure crystal which are measured in absorption. Pair transitions to J=1and2 are obscured by strong vibronic transitions. A spin-dependent dipole moment resulting from the Cr3+-Eu3+ exchange is invoked to explain the emission. This requires the three t2g chromium orbitals to be inequivalent. The term which is isotropic in the europium orbitals results in pair emission to J=1. The transitions to J>1 occur from terms which contain the orbital dependence of the europium electrons. The experimental observation of pair transitions to levels with J>1 verifies the existence of europium electron anisotropy in the Cr2+-Eu3+ exchange interaction. © 1969 The American Physical Society.