SrTiO₃:Eu³⁺ phosphors prepared by sol-gel synthesis: Structural characterization, magnetic properties and luminescence spectroscopy study

Abstract

We report the results of the comprehensive study of the structural, magnetic and optical properties of SrTiO₃ perovskite doped with Eu³⁺ ions. Polycrystalline powders were obtained by sol-gel process including high-temperature annealing at 1300 °C. The structural analysis showed that material is composed of several phases with dominant SrТiO₃ and onsiderable quantity of titanium dioxide (rutile, 10…20%). Both the amount of Eu and ratio of Eu:Sr in the final product are considerably smaller as compared to the original solutions for synthesis. The elemental analysis reveals europium only in the phase of EuSrTi₂O₇ compound for equimolar ratio of Eu and Sr during the synthesis. The EPR analysis reports deficiency of Eu²⁺ in the samples under investigations. SrTiO₃:Eu³⁺ powders demonstrate weak photoluminescence, which intensity grows up with increasing the concentration of Eu and reaches its maximum at c.a. 8 mol.% of Eu in the original solutions. Addition of Al increases the intensity of photoluminescence (c.a. 2.2 for 10 mol.%). Emission spectra are typical for Eu³⁺ occupied sites with high symmetric environment (dominant ⁵D₀→⁷F₁ transition) with relatively low distortion (both ⁵D₀→⁷F₂ and ⁵D₀→⁷F₄ as well present, but with a lower intensity) of coordination polyhedron. Low solid-solubility limit of Eu³⁺ in perovskite matrix (less than 1 mol.%), peculiarities of optical spectra, effect of Al, production/annealing temperature dependence etc. have suggested that structural effects are dominating in functional, in particular, optical properties of SrTiO₃:Eu³⁺ phosphors.