Tuneable photoluminescence of β-K2SO4 phosphors with enhanced thermal stability and quantum efficiency by chemical substitution

In this work, a novel Orthosilicate-Orthophosphate structure phosphor K1-x(BaSr) (1+x)/2(SixP1-x)O4: Eu2+ (0 ≤ x ≤ 1) with superior quantum efficiency and excellent thermal stability was designed for the application of next-generation high-power white light-emitting diodes (WLEDs). The Rietveld refinement shows the isotopic co-substitution of P5+ and K+ for Si4+ and Ba2+/Sr2+, generating a continuous change of centroid shift and crystal field splitting, further contributing to tuneable light from blue to green emission. Moreover, the excellent quantum efficiency stems from the widened bandgap and the defect-associated electron traps. Using experimental and density functional theory calculation, we confirm the potential mechanism of enhanced thermal stability, in which the co-substitution-induced crystal size mismatch brings the trapped electrons to move from defect levels to a higher energy state (conduction band) and then continue radiative transition. This work provides valuable insights into the design of other phosphors with enhanced thermal stability and quantum efficiency.