Processing-dependence and the nature of the blue-shift of Bi³⁺-related photoemission in ScVO₄ at elevated temperatures

We report on the mechanism of photoemission from Bi³⁺-related centers in ScVO₄. In this material, an unusually strong red photoluminescence was recently observed and was related to hypothetic interactions between oxygen vacancies and Bi³⁺ species, denoted as oxygen vacancy perturbation. Here, we provide further experimental evidence for the existence of an interrelation between the availability of oxygen and the blue-shift of Bi³⁺ photoluminescence. For this, the effect of preparation conditions and the temperature-dependence of the spectroscopic properties of ScVO₄:Bi³⁺ are studied. Under a reducing atmosphere, as a result of vanadate reduction from V⁵⁺ to V³⁺, a structural change occurs at high temperature from ScVO₄ to ScVO₃. However, this transition is avoided through mild treatment for short times. Then, instead of a crystallographic change, different types of defects, which assumedly partition in the vicinity of the Bi³⁺ dopants, could be locally generated at the expense of oxygen vacancies. As a result, Bi³⁺ luminescence occurs at higher energy. Similar but considerably smaller blue-shift is confirmed due to thermal inversion from ³P₀ to ³P₁ because the Bi³⁺ photoluminescence was measured at elevated temperature. On the basis of these results, we believe that the careful engineering of the local defect environment around Bi³⁺ and the distribution between the excited states of ³P₀ and ³P₁ can tailor the spectral properties of future Bi³⁺-based phosphor materials.