Optical absorption and electron paramagnetic resonance studies of Cr3+-doped Y3Ga5O12 phosphor

Y3Ga5O12 powder doped with Cr3+ ions was prepared, and was characterized by powder X-ray diffraction analysis. Typical absorption spectra of Cr3+ in octahedral symmetry contained several spin-allowed absorption bands, of which four were usually well resolved. Absorption bands at 268, 373, 438, and 612 nm were assigned to the 4A2g (F) → 4T1g (P), 4A2g (F) → 2A1g (G), 4A2g (F) → 4T1g (F), and 4A2g (F) → 4T2g (F) transitions, respectively. In EPR spectra, two resonance signals with g = ~4.03 and ~1.92 and g = ~4.79 and ~1.92 were observed at room temperature and 123 K, respectively. The low-field line of the spectrum was attributed to isolated Cr3+ ions and the high field line mainly to Cr3+–Cr3+ exchange-coupled pairs. The Cr3+ crystal field and spin Hamiltonian were evaluated from the resonance line positions observed in the EPR spectra. The nature of bonding in the crystal is discussed on the basis of correlation of optical and EPR data.