Effect of annealing conditions on structural and luminescencent properties of Eu ³⁺ -doped Gd ₂ Ti ₂ O ₇ thin films

Here we report on preparation of Eu ³⁺ -doped Gd ₂ Ti ₂ O ₇ 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 ∼20 nm in the as-deposited to ∼60 nm in the crystalline sample annealed at 1100 °C. Scanning electron microscopy showed dense films with the uniform thickness of about 700 nm. 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 Eu ³⁺ 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.