Site-Selective Luminescence of Eu3+ Ions in Silicate-Tungstates: A Study on Spectroscopic Features with Apatite and Scheelite Structures

The present work studies europium-ion spectroscopic features in solid solutions based on silicate-tungstates Ca2La6.8Eu1.2Si5.6W0.4O26.4 and Ca8Eu2Si3W3O26 microcrystalline powders with the crystal structure of silicate apatite and scheelite respectively. Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. In simpler terms, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectroscopy, primarily in the electromagnetic spectrum, is a fundamental exploratory tool in the fields of astronomy, chemistry, materials science, and physics, allowing the composition, physical structure and electronic structure of matter to be investigated at the atomic, molecular and macro scale, and over astronomical distances. The spectroscopic features were studied by means of photoluminescence spectroscopy and X-ray excited luminescence at temperatures 4.6, 90 and 295 K. In Ca2La6.8Eu1.2Si5.6W0.4O26.4 only intensive luminescence was observed, which was characterized by a set of 5D0 7FJ dominant intraconfigurational transitions for Eu3+ ion. In Ca8Eu2Si3W3O26, both 5D0 7FJ intraconfigurational transitions for Eu3+ ion and wide 430 nm emission band corresponding to host self-trapped exciton (STE) emission are observed. This STE emission band is reabsorbed by the f – f absorption of Eu3+ ions by means of energy transfer from host to Eu3+. The asymmetry coefficient which characterizes the shape of the emission spectrum of Eu3+ ions strongly depends on the energy of exciting photons. The Eu3+ ion might occupy two nonequivalent crystallographic sites. Some features of this phenomenon were discussed.