Photoluminescence tuning in a novel Bi3+/Mn4+ co-doped La2ATiO6:(A = Mg, Zn) double perovskite structure: phase transition and energy transfer

Abstract

Red-emitting phosphors are indispensable compounds which are used to achieve a warm white light in phosphor-converted white light emitting diodes (pc-WLEDs). However, the luminous efficiency and stability of red phosphors are still big challenges. In this work, we developed red-emitting double perovskite phosphors La₂ATiO₆:Bi³⁺,Mn⁴⁺ (A = Mg, Zn) (LAT:Bi³⁺,Mn⁴⁺) and discuss the relationship between the double perovskite phosphor structure and the luminescence performance in detail. According to the Rietveld refinement results for the La₂Mg_(1−w)Zn_wTiO₆:Bi³⁺,Mn⁴⁺ (0 ≤ w ≤ 1) (LM_(1−w)Z_wT:Bi³⁺,Mn⁴⁺) solid solution, the proposed mechanism of the spectral adjustment is ascribed to the appearance of the phase transition, which results in a lower local structural symmetry of the [LaO₁₂] polyhedron and the variation of the crystal field environment for Mn⁴⁺. Notably, this is the first time that the influence of the local structure variation on the luminescence tuning in double perovskite structure phosphors has been revealed, and this could offer guidance for the development of new phosphor system. By designing Mg²⁺/Zn²⁺ cation substitution, the internal quantum efficiency (IQE) is remarkably enhanced beyond 20%. In addition, we succeeded in achieving a Bi³⁺/Mn⁴⁺ co-doped energy transfer in the double perovskite structure phosphors. Owing to the Bi³⁺ → Mn⁴⁺ energy transfer in LAT, the red emission of the Mn⁴⁺ ions could be dramatically enhanced. The energy transfer efficiency of LAT:Bi³⁺,Mn⁴⁺ eventually exceeded 90%. The IQE and the thermal stability were all enhanced by around 30% compared to the non-co-doped samples, respectively. These results indicate that the Bi³⁺ → Mn⁴⁺ energy transfer strategy could play a pivotal role in the development of highly efficient red-emitting phosphors. 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 warm pc-WLEDs.