Broad Excitation Band and High Efficiency of Red Phosphor Caused by Eu3+-Induced Phase Transition in LiKBi2(MoO4)4

A red phosphor LiKBi2(MoO4)4:Eu3+ was synthesized at 600 °C via a solid-state reaction. Eu3+ doping (>20 mol %) triggers a phase transition (tetragonal → monoclinic), inducing severe [EuO8] polyhedral distortion (D = 0.1002). This structural rearrangement enables an unprecedented broad excitation band (200–400 nm, fwhm >120 nm), identified by DFT and semiempirical modeling as dominated by Bi3+→Mo6+ metal–metal charge transfer (MMCT), with part contributions from Bi3+ 6s→6p and O2–→Mo6+/Eu3+ charge transfers. The optimized LiKBi0.8Eu1.2(MoO4)4 phosphor achieves record efficiencies under 350 nm excitation: IQE = 97%, EQE = 84.7%. Linear thermal response (298–473 K, R2 = 0.994) exhibits high relative sensitivity (Sr = 1.3147% K–1 at 473 K). Combined with a 365 nm UV chip, it delivers warm white light (Ra = 87.3, CCT = 3464 K) with 25.82 lm/W efficacy. This work provides a cost-effective, high-performance red phosphor for high-CRI lighting and high-temperature sensing and implements a structural design strategy for spectral regulation.