Enhancing Abnormal Thermal Quenching Characteristics of Y 1– x La x NbO 4 :Pr 3+ Phosphors through Energy Transfer Enhancement and Intervalence Charge Transfer Modulation Synergistic Strategy

The abnormal thermal quenching characteristics of phosphors are crucial for enhancing the lighting quality and improving the sensitivity of optical thermometry. How to enhance the abnormal thermal quenching characteristics of phosphors is a great challenge. In this work, based on (Y_1-xLa_x)_0.995NbO₄:0.005Pr³⁺ (x = 0.00, 0.25, 0.50, 0.75, and 1.00) (Y_1-xLa_xNbO₄:Pr³⁺) phosphors with the Nb⁵⁺-O^2- charge transfer band (CTB) and Pr³⁺-Nb⁵⁺ intervalence charge transfer (IVCT) bands, a synergistic strategy of CTB energy transfer enhancement during the heating and IVCT band displacement modulation is proposed to enhance the abnormal thermal quenching characteristics. In addition, with the increase of La³⁺ with a larger ionic radius, the Pr³⁺-Nb⁵⁺ bond length also increases, resulting in the increase of the IVCT band from 4.05 to 4.19 eV; thus, the Pr³⁺³P₀ → ¹D₂ electron transfer through the IVCT channel becomes more challenging. However, thermal activation allows ³P₀ → ¹D₂ electron transfer to occur at higher temperatures, thereby enhancing ¹D₂ → ³H₄ emission. In addition, the enhanced energy transfer of [NbO₄]^3- → Pr³⁺ due to increased La³⁺ substitution enhances the ¹D₂ → ³H₄ emission integral intensity at 498 K from 148 to 436%. The synergistic strategy of CTB energy transfer enhancement during heating and IVCT band displacement modulation provides a new idea for developing and designing strong abnormal thermal quenching phosphors.