Regulating Luminescence Thermal Quenching of Praseodymium-Doped Niobo-Tantalate Phosphor through Intervalence Charge Transfer Band Displacement.

Pr-related intervalence charge transfer (IVCT) bands are a research hotspot owing to their amelioration in the luminescence thermal quenching of Pr-activated phosphors. Here, a typical IVCT band displacement strategy via a topological chemical scheme is reported to optimize the luminescence thermal quenching performance of praseodymium-doped niobo-tantalate. The substitution of Ta ions for Nb ions reduces the valence-weighted average cation optical electronegativity and increases the bond lengths of the activator (Pr) to the ligand cations (Nb and Ta) via adjusting the crystal structure, leading to an increase in the IVCT energy level position from 3.521 to 4.139 eV. The increase in the IVCT energy level leads to an increase in the number of electrons located in the Pr P energy level, which compensates for the emission of D during warming. Especially, the energy gap value of the IVCT band is positively correlated with the thermal quenching activation energy Δ. Δ increases, the crossover point rises, and the nonradiative transition decreases, further enhancing the Pr D emission. At 503 K, the D emission integral intensity increases from 14 to 224% relative to the 303 K original integral intensity. This IVCT band displacement strategy can be used as a scheme for designing antithermal quenching luminescence materials.