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 O^2–→Mo⁶⁺/Eu³⁺ charge transfers. The optimized LiKBi_0.8Eu_1.2(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 (S_r = 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.