Role of energy band structure on the luminescence performance of double perovskite La₂LiMO₆:Eu³⁺ (M=Sb, Ta, Nb) red emitting phosphors

Monoclinic double perovskite La₂LiMO₆:Eu³⁺(M = Sb, Ta, Nb) phosphors were prepared by high temperature solid state reaction method in air. The material microstructures were characterized by XRD Rietveld refinement. All La₂LiMO₆:Eu³⁺ exhibited Eu³⁺ - emission in the red region under excitation by ultraviolet-blue light at room temperature. In the order of M = Sb, Ta, Nb, the emission of Eu³⁺ in La₂LiMO₆:Eu phosphor declined under charge transition band (CTB) excitation in turn, while enhanced gradually under 394 nm and 465 nm excitation. The optical band gap energy was calculated through the UV–Vis reflectance spectra of La₂LiMO₆:Eu indicating that photoionization is the quenching scheme in La₂LiMO₆:Eu. Co - doped with Bi³⁺ ions further reduces the energy band (i.e. forbidden bandwidth) of LLN:Eu, resulting in the significant enhancement of Eu³⁺- emission under 465 nm excitation, which demonstrates its potential application value as the red component of a blue chip based-white LED.