Chromium recharging processes in the Y3Al5O12:Mg,Cr single crystal under the reducing and oxidizing annealing influence

Abstract

The influence of reducing and oxidizing annealing on optical absorption spectra of the yttrium aluminium garnet (YAG) single crystal co-doped with Mg and Cr is investigated using step-by-step isothermal and isochronous thermal treatment in H2 or air flow. The changes in the spectral were analyzed using decomposition on elementary absorption bands of Gaussian shape. The separated absorption bands attributed to the Cr4+ ions occupying octahedral and tetrahedral sites in garnet lattice demonstrate different behavior. The analysis allows to distinguish the electronic recharging process Cr4+ $ARLR Cr3+ taking place in the octahedral sites of garnet lattice and having lower activation energy from the chromium migration process Cr4+ $ARLR Cr4+ happening at higher temperatures or longer exposure. Estimations show that approximately 0. 2 percent of total number of chromium ions occupied tetrahedral sites forming phototropic centers in the YAG: Mg, Cr crystal.