New insights in the structure–luminescence relationship of Eu:SrAl 2O 4

Abstract

This work aims the preparation of Eu:SrAl 2O 4 through a sol–gel methodology. Some studies point out the possibility that hexagonal polymorph exhibit higher luminescence efficiency than the monoclinic one. However, the slow diffusion processes in the solid-state reactions require the use of fluxing agents, like B(III) ions, to reduce the synthesis temperature, thus favouring the formation of the monoclinic phase and avoiding the stabilization of the hexagonal one. For that, the synthesis proposed in this work allows to prepare pure hexagonal and monoclinic polymorphs without the use of any fluxing agent. The influence of Eu-doping level and firing temperature in the crystalline structure and optical properties of both polymorphs are studied by means of X-ray diffraction, Raman scattering, absorption, excitation and emission spectroscopy. Emission spectra reveal the existence of energy transfer between the monoclinic matrix and the Eu 2+ ion, but the luminescence efficiency is not influenced by the crystalline polymorph but it mainly depends on the firing temperature.