Tuning oxygen vacancy photoluminescence in monoclinic Y₂WO₆ by selectively occupying yttrium sites using lanthanum

The effect of isovalent lanthanum (La) doping on the monoclinic Y₂WO₆ photoluminescence was studied. Introducing the non-activated La³⁺ into Y₂WO₆ brings new excitation bands from violet to visible regions and strong near-infrared emission, while the bands position and intensity depend on the doping concentration. It is interesting to find that doping La³⁺ into Y₂WO₆ promotes the oxygen vacancy formation according to the first-principle calculation, Raman spectrum, and synchrotron radiation analysis. Through the Rietveld refinement and X-ray photoelectron spectroscopy results, La³⁺ is found to mainly occupy the Y2 (2f) site in low-concentration doped samples. With increasing doping concentration, the La³⁺ occupation number at the Y3 (4g) site increases faster than those at the Y1 (2e) and Y2 (2f) sites. When La³⁺ occupies different Y sites, the localized energy states caused by the oxygen vacancy pair change their position in the forbidden band, inducing the variation of the excitation and emission bands. This research proposes a feasible method to tune the oxygen vacancy emission, eliminating the challenge of precisely controlling the calcination atmosphere.