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 χopt(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.
Lv et al. (2026) studied this question.