A study of optical properties and site preference of Bi³⁺/Eu³⁺ co-doped CaLa₄Si₃O₁₃ red-emitting phosphors for w-LED applications

Eu³⁺ ions are commonly employed as emitting centres for red phosphors, which suffer from the small absorption cross-sections. In this work, Bi³⁺ ions are used to sensitize Eu³⁺ ions in CaLa₄Si₃O₁₃ host as an attempt to enhance the Eu³⁺ emission. The site preference of Bi³⁺ ions is investigated in detail. The emission peak at 400 and 430 nm can be ascribed to the Bi³⁺ in La2 and La1 sites, respectively. The reduction of emission intensity and the shortened lifetime of Bi³⁺ ions suggest that efficient energy transfer from Bi³⁺ to Eu³⁺ ions. Moreover, the Bi³⁺ ions in the La1 sites are confirmed to be more efficient sensitizers for Eu³⁺ ions owing to the more significant spectral overlap than the Bi³⁺ ions in the La2 sites. The thermal stability of the synthesized phosphors is superior or comparable with other reported Bi³⁺/Eu³⁺ co-doped phosphors, which is not affected by the site preference of Bi³⁺ ions. The results suggest that Bi³⁺ ions are efficient sensitizers for Eu³⁺ ions and the prepared phosphors can be potentially employed as red-emitting component for w-LED applications.