Oxygen Vacancy Effect on Photoluminescence Properties of Self-Activated Yttrium Tungstate

A series of single-phase yttrium tungstate powders were synthesized through solid-state reaction under air or argon atmosphere. All powders showed broad band emission in the visible light region, and the argon-calcined samples presented strong near-infrared luminescence. Moreover, the long-wave excitation bands peaking at 340, 378, 380, 490, and 523 nm depended critically on the calcination atmosphere and temperature. The emergence of these new excitation bands was ascribed to different oxygen vacancy concentrations with the analysis of the first-principle calculation, Raman and X-ray absorption fine structure spectra. The oxygen vacancies caused the reduction of the average coordination number of tungsten, and the position of the localized energy band changed with the oxygen vacancy concentration. Finally, a schematic photoluminescence excitation model was proposed via anion and cation charge transfer. The obtained results promise to be very useful in interpreting self-activated tungstate luminescence mechanism. They can also serve as guide line for tuning the luminescence performance of yttrium tungstate and related materials.