Defect-induced optical absorption and photoluminescence of Verneuil-grown SrTiO 3 crystal

Abstract

In order to clarify the mechanism of the photoluminescence (PL) and other photo-induced effects observed for Verneuil-grown SrTiO 3 crystal, a nominally pure dark-blue as-grown crystal, which has high DC conductivity ( σ ≃ 1 0 - 3 Ω - 1 cm - 1 ) and high dielectric constant ( ε > 1 0 6 at 1 kHz) at room temperature, was prepared and annealed at 973 K in a 90% Ar–10% H 2 mixture gas stream. The optical density (OD) and PL spectra were studied at the different stages of the annealing. In addition to the band gap absorption, at least eight intense optical absorptions due to crystal defects are observed around about 2.9, 2.4, 2.2, 2.1, 1.7, 0.82 and 0.27 eV for the as-grown crystal. With progressing annealing, these absorptions became weak and the crystal became a colorless-transparent insulator. We have found a reasonable connection between the OD spectra and the PL ones.