Role of oxygen vacancy in rare-earth-free LiCa₃Mg(VO₄)₃ phosphor: Enhancing photoluminescence by heat-treatment in oxygen flow

As a kind of white light emitting diode (w-LED) with many advantages, rare-earth-free vanadate phosphor has attracted more and more attention. The oxygen vacancies and other surface defects in vanadate oxide have obvious effects on its structure and properties. In order to reveal the specific effects, we heat-treat the original LiCa₃Mg(VO₄)₃ (LCMV) in an oxygen flow with different time to decrease oxygen vacancies, and find that the lattice distortion of [VO₄] tetrahedron caused by oxygen vacancy is effectively reduced. Meanwhile, the crystallinity of the treated samples increases, the surface defects decreases, and the fluorescence intensity increases. The variation of photoluminescence quantum yield (PLQY) with oxygen treatment time is as follows: the enhancement effect firstly reaches the strongest (69.34 %) within one hour, then begins to decline after two hours, and finally reaches the platform after three hours and remains basically unchanged. The reason for the enhancement of PLQY is the decrease of oxygen vacancy after one-hour treatment, and the reason for the decrease of PLQY after a further increased treatment time is that the absorption of oxygen and water in air caused by excessive surface defects introduced by oxygen treatment.