Tuning luminescence thermal quenching performance of KxMgxSc1.95−xMo3O12:5%Eu3+ phosphor via synergistic negative thermal expansion and charge compensation effects†

Negative thermal expansion (NTE) compounds offer significant opportunities for advancing our understanding of thermal expansion phenomena and their applications in various fields. However, the unique properties arising from anomalous lattice effects of NTE materials remain underexplored for addressing luminescence thermal quenching, particularly through cation substitution in NTE-based host materials. In this study, we have synthesized K_xMg_xSc_1.95−xMo₃O₁₂:5%Eu³⁺ phosphors (x = 0, 0.4, 0.7, 1.0) and investigated their crystal structure, microstructure, and thermal expansion properties utilizing temperature-dependent synchrotron radiation, scanning electron microscopy, and temperature-dependent Raman spectroscopy. The corresponding phosphor with x = 0.4 possesses near-zero expansion with α_V = −0.58 × 10⁻⁶ K⁻¹, while those with x = 0.7 and 1.0 show positive thermal expansion with thermal expansion coefficient α_V = 2.82 and 3.59 × 10⁻⁶ K⁻¹, respectively. Furthermore, we have assessed their luminescence thermal stability and the underlying mechanisms through temperature-dependent UV-visible absorption, photoluminescence excitation, and emission spectra spectroscopy. Interestingly, K_0.4Mg_0.4Sc_1.55Mo₃0₁₂:5%Eu³⁺ and K_0.7Mg_0.7Sc_1.25Mo₃0₁₂:5%Eu³⁺ exhibit significant thermal stability, whereas KMgSc_0.95Mo₃0₁₂:5%Eu³⁺ demonstrates strong thermal quenching. Among these phosphors, K_0.4Mg_0.4Sc_1.55Mo₃0₁₂:5%Eu³⁺ exhibits negative thermal quenching behavior, retaining 182% of its initial intensity measured at 300 K, even at 700 K. The luminescence decay analysis indicates that the resistance to thermal quenching arises from the synergistic effects of the NTE of the host and K⁺ charge compensation. This work has explored a cation substitution strategy for NTE-based phosphors to introduce a novel near-zero thermal expansion material and identify a red phosphor with wide-temperature-range thermal stability.