Vanadium in yttrium aluminum garnet: charge states and localization in the lattice

TL;DR

This study investigates the charge states, localizations, and optical properties of vanadium ions in yttrium aluminum garnet (YAG) crystals using optical absorption and EPR measurements, revealing charge transformations and site-specific behaviors.

Contribution

It provides detailed analysis of vanadium charge states and their lattice site occupations in YAG, including high-frequency EPR parameters and theoretical energy level calculations.

Findings

V3+ occupies both octahedral and tetrahedral sites in as-grown crystals.

Annealing in air induces V3+ to V4+ charge transformation.

Optical and EPR data enable accurate assignment of absorption peaks.

Abstract

Vanadium ions charge states and their incorporation in the yttrium aluminum garnet Y3Al5O12 (YAG) lattice were studied by the correlated optical absorption and electron paramagnetic resonance (EPR) measurements. In as-grown crystals, the occupation of the V3+ at both the octahedral and tetrahedral aluminum sites was proven. The V3+ to V4+ charge transformation was observed after annealing in air, whereas annealing in the hydrogen atmosphere resulted exclusively in a slight weakening of the V3+ absorption bands due to partial recharge of these ions. Spin Hamiltonian parameters of the V3+ and V4+ ions at the tetrahedral sites including the zero field splitting and the 51V 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 V3+ and V4+ ions were calculated. The charge distribution over the tetrahedral V3+ and its nearest oxygen surroundings was found to be strongly inhomogeneous whereas the tetrahedral V4+ 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.