Structural, optical, and photoluminescent properties of sol–gel derived Eu-doped Ba_1−xSr_xTiO₃ thin films

Abstract

Eu-doped Ba_1−xSr_xTiO₃ (x = 0, 0.2, 0.3, and 0.4) thin films with Eu-doping content of 1 mol% have been prepared on fused silica substrates by a chemical solution deposition method and characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), optical and photoluminescence measurements. XRD analysis showed that the films were well crystallized with a pure perovskite structure in the annealing temperature range from 650 to 750 °C. AFM observation indicated that the films were dense and smooth. The band-gap energies of the thin films were also investigated. The more the Sr content in the thin films, the narrower the energy gap of the thin films. Photoluminescence spectra of the thin films showed two prominent transitions of Eu³⁺ ions at 594 nm (⁵D₀ → ⁷F₁) and 618 nm (⁵D₀ → ⁷F₂) upon excitation at 395 nm (⁷F₀ → ⁵L₆). The observed changes of luminescence spectra by the decrease of the intensity ratio R, which was defined as the ratio of the integrated emission intensity of ⁵D₀ → ⁷F₂ transition to that of ⁵D₀ → ⁷F₁ transition, were associated with the increase of the inversion symmetry of Eu³⁺ sites when Sr content increased. Lifetime study of photoluminescence indicated that the average lifetime of the thin films was approximately 0.7 ms.