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Vanadium ions charge states and their incorporation in the yttrium aluminum garnet Y 3 Al 5 O 12 (YAG) lattice were studied by the correlated optical absorption and electron paramagnetic resonance (EPR) measurements. In as-grown crystals, the occupation of the V 3+ at both the octahedral and tetrahedral aluminum sites was proven. The V 3+ to V 4+ charge transformation was observed after annealing in air, whereas annealing in the hydrogen atmosphere resulted exclusively in a slight weakening of the V 3+ absorption bands due to partial recharge of these ions. Spin Hamiltonian parameters of the V 3+ and V 4+ ions at the tetrahedral sites including the zero field splitting and the 51 V hyperfine constants have been determined using the high-frequency, up to 300 GHz, EPR measurements. From the analysis of the spin Hamiltonian parameters in the framework of the crystal field theory, the ground state energy levels splitting of the V 3+ and V 4+ ions were calculated. The charge distribution over the tetrahedral V 3+ and its nearest oxygen surroundings was found to be strongly inhomogeneous whereas the tetrahedral V 4+ ion concentrated the charge with very weak participation of surrounding ligands. Furthermore, the correlation of the optical and EPR data allowed the proper assignment of the optical absorption peaks in YAG:V crystals.

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Cerium doped rare-earth aluminum garnets represent an important class of scintillation and luminescent materials widely used in different technical fields including the medical imaging and the solid state white light...

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