Effect of annealing conditions on structural and luminescencent properties of Eu3+-doped Gd2Ti2O7 thin films

Abstract

Here we report on preparation of Eu3+-doped Gd2Ti2O7 pyrochlore luminescent thin films by pulsed laser deposition technique and their structural, morphological and optical characterization. The influence of annealing temperature and background gas (air vs. argon) on film photoluminescence is examined for the optimization of post-deposition annealing conditions. As-deposited amorphous films become pure pyrochlore crystalline after calcination at temperatures higher than 1000°C. Atomic force microscopy showed increase in the grain size from ∼20nm in the as-deposited to ∼60nm in the crystalline sample annealed at 1100°C. Scanning electron microscopy showed dense films with the uniform thickness of about 700nm. Luminescence spectra of crystalline films were complex and composed of better resolved emission lines than in the amorphous sample. Emission spectra showed that symmetry of Eu3+ sites become disturbed in annealed films due to the extrinsic thermal stress. Films treated in argon displayed similar emission and excitation spectral features like air-treated ones, but with better resolved emission lines. Calculated quantum efficiency of emission showed that optimization of annealing conditions led to an enhancement of films luminescence. The highest quantum efficiency of emission and the longest lifetime is found for the sample annealed at 1100°C in presence of argon.