Energy transfer, structural and luminescent properties of the color tunable phosphor Y2WO6:Sm3+

Abstract

Inorganic phosphors based on monoclinic Y2WO6 doped with Sm 3+ ions were prepared via conventional solid-state reactions at high temperature. A total of six samples were obtained with different Sm 3+ concentrations (0-9%). The purity of the as-prepared phases was checked by powder X-ray diffraction (PXRD). The excitation, emission, and time-resolved emission spectra were examined in detail. The experimental decay curves were fitted to the Inokuti-Hirayama model, showing that the Sm 3+ ions form clusters at all compositions.Periodic hybrid density functional theory calculations were also carried out on the undoped material and on 144-atom supercells of stoichiometry Y1.9375Sm0.0625WO6 and Y1.875Sm0.125WO6. The different coordination environments at the Y1, Y2 and Y3 sites are analysed in detail. The calculated structure and band gap of Y2WO6 are in good agreement with experiment with one potentially important discrepancy in a Y3-O bond length. The thermodynamically favoured substitution sites for Sm, Y2 and Y3, in the supercell are not those observed under the preparation conditions used here, since the experimental Rietveld analysis suggests occupation of Y1 at all concentrations. Analogous calculations for the Eu-doped system highlight marked differences between Eu and Sm despite their similar ionic sizes. The calculated densities of states show the position of the 4f levels in the band gap depend on the 2 sites occupied by the dopants and thus expect marked differences in the luminescence spectra, opening up possibilities for tuning device performance.