Dual-Energy-Band Coordinated Modulation via Charge Transfer and Intervalence Charge Transfer for Regulating...

Intervalence charge transfer (IVCT) bands in Pr³⁺-activated phosphors exhibit tunable Pr³⁺³P₀ and ¹D₂ luminescence thermal quenching properties, playing a significant role in solid-state lighting and optical thermometry. However, strong IVCT → ³H₄ nonradiative transitions pose a significant challenge to the widespread application of Pr³⁺-activated phosphors. In this work, the substitution of Nb⁵⁺ by Ta⁵⁺ with a weaker electron-withdrawing ability reduces the optical electronegativity χ_opt(Mⁿ⁺), weakens the nephelauxetic effect, shortens the Nb/Ta-O bonds, increases the host crystal-field splitting, and decreases the Pr-Nb/Ta distance. Consequently, the charge-transfer bands (CTBs) and IVCT bands increase from 4.68 and 4.05 to 4.71 and 4.19 eV. Specifically, the reduction of the relative energy-level gaps ΔE₁ from 0.63 to 0.52 eV results in thermal activation, enabling more electrons from the IVCT band to transfer to the 4f5d energy level or CTB. Furthermore, under 4f5d energy-level excitation, the relative integral intensity of Pr³⁺¹D₂ emission in the x = 0.50 sample reaches 242.31% at 498 K compared to that at 298 K. This dual-energy-band coordinated modulation mechanism of CTB and IVCT bands provides new insights for developing and designing novel antithermal quenching or highly sensitive optical thermometry phosphors.