Photoluminescence Tuning in Novel Bi3+/Mn4+ Co-doped La2ATiO6:(A = Mg, Zn) Double Perovskite Structure: Phase Transition and Energy Transfer

摘要： Red-emitting phosphors are indispensable componans to achieve warm white light of phosphor-converted white light emitting diodes (pc-WLEDs). However, the luminous efficiency and stability for red phosphors are still a big challenge. In this work, we develop red-emitting double perovskite phosphors La2ATiO6:Bi3+, Mn4+ (A = Mg, Zn) (LAT: Bi3+, Mn4+) and disscuss the relationship between double perovskite phosphors structure and luminescence performance in detail. By designing Mg2+/Zn2+ cation substitution, It is noteworthy that the internal quantum efficiency (IQE) is remarkeblely enhanced beyond 20%. According to Rietveld refinement results for La2Mg(1-w)ZnwTiO6:Bi3+, Mn4+ (0 ≤ w ≤ 1) (LM(1-w)ZwT:Bi3+, Mn4+) solid solution, the proposed machanism of the spectral adjustment is ascribed to the appearance of phase transition, which results in a lower local structure symmetry of [LaO12] polyhedron and variation of crystal field environment for Mn4+. Notably, it is the first time to reveal the influence of local structure variation on luminescence tuning in double perovskite structure phosphors, which could offer a guidance to develop new phosphors system. In addition, we firstly succeed in realizing Bi3+/Mn4+ co-doped energy transfer in double perovskite structure phosphors. Due to the Bi3+→Mn4+energy transfer in LAT, red emission of Mn4+ ions could be dramatically enhanced. The energy transfer efficiency of LAT: Bi3+, Mn4+ eventually reaches exceed 90%. The IQE and thermal stability are all enhanced around 30% than non-codoped samples, respectively. These results indicate that Bi3+→Mn4+energy transfer strategy could play a pivotal role in developing highly efficient red-emitting phosphor. The performance of the fabricated pc-WLEDs devices indicates that LAT:Bi3+, Mn4+ could be a promising red phosphor for near ultraviolet (n-UV) based on warm pc-WLEDs.