Optical and electron spin resonance spectroscopy of Ti3+ and Ti4+ in Al2O3

Abstract

The absorption spectrum of Ti³⁺:Al₂O₃ crystals grown in a reducing atmosphere consists of the main blue‐green absorption band and a weak infrared band. This infrared absorption decreases in intensity on annealing the as‐grown samples in a reducing atmosphere. The analysis of electron spin resonance spectra of the as‐grown samples, in which the infrared absorption band is observed, indicates that the center associated with the band is a cluster involving Ti³⁺ and Ti⁴⁺ ions with a neighboring, charge compensating Al³⁺ vacancy. The coexistence of a Ti⁴⁺ ion and an Al³⁺ vacancy in the neighborhood of the Ti³⁺ ion weakens the crystal field at this ion more than a single Ti⁴⁺ ion, giving rise to a red shift of the Ti³⁺ absorption.