Development of a potential optical thermometric material through photoluminescence of Pr³⁺ in La₂MgTiO₆

In this work, we demonstrate a potential thermometric material after systematic studies on the concentration/temperature-dependent spectroscopic properties of Pr³⁺ excited multiplets and of the Pr³⁺-Ti⁴⁺ intervalence charge transfer (IVCT) state in (La_1-xPr_x)₂MgTiO₆. The experimental results indicate that the electron population efficiency between the involved Pr³⁺ 4f multiplets is directly governed by multi-phonon relaxation (MPR) and cross relaxation (CR), and the IVCT state provides an additional contribution to the ¹D₂ luminescence. A schematic energy level diagram is proposed to illustrate the electron population pathway in Pr³⁺ doped La₂MgTiO₆. The observations clarify that the dramatic thermal-quenching of ³P₀ luminescence is mainly induced by the electronic configuration crossover between the ³P₀ multiplet and the IVCT state. On the other hand, the ¹D₂ luminescence possesses an excellent thermal stability in a large temperature region. These temperature sensing features of the Pr³⁺ doped La₂MgTiO₆ material indicate its potential application in optical thermometric techniques.