Excitation Wavelength Dependent Luminescence of LuNbO4:Pr3+—Influences of Intervalence Charge Transfer and Host Sensitization

A series of LuNbO4:Pr3+ phosphors was prepared by a solid-state reaction method at high-temperature. Rietveld refinements were performed based on powder X-ray diffraction (XRD) data. Diffuse reflectance spectra (DRS), UV–vis photoluminescence (PL), time-resolved emission spectra (TRES), and fluorescence decays were utilized to study the luminescence and host sensitization processes of Pr3+ in LuNbO4. Excitation wavelength dependent luminescence of LuNbO4:Pr3+ was investigated and explained in consideration of the processes of nonradiation relaxation via cross-relaxation, multiphonon relaxation, and crossover to the intervalence charge transfer (IVCT) state. Furthermore, the host sensitization of Pr3+ emission in LuNbO4 was confirmed and the energy transfer efficiency from host to Pr3+ increased with increasing Pr3+ doping concentration/temperature. Because the change of emission intensities for both blue from the host and red from 1D2 is sensitive to temperature, a large variation of emission color is observed between RT and 500 K.