Blue light excited Li6CaLa2M2O12:Eu3+ (M=Ta, Sb) red-emitting phosphors: structure and photoluminescence properties

A series of blue light excitable phosphors Li6CaLa2M2O12:xEu3+ (M=Ta, Sb; 0≤x≤0.6) were prepared by solid state reaction. Crystal structure, absorbance, photoluminescence excitation, emission and concentration dependence of Eu3+ luminescence were investigated. The exact spectral assignments can be performed by the analysis of the absorption spectra in combination with PLE spectra. The dominant red emission from 5D0-7F2 transition of Eu3+ can be effectively excited by 464 nm (blue light), which matches well with GaN-based blue LED chips. The optimal concentration of Li6CaLa2Ta2O12:xEu3+ and Li6CaLa2Sb2O12:xEu3+ are 50 mol% and 40 mol%, respectively. The critical energy transfer distance between Eu3+ has also been calculated by the concentration quenching method. In addition, the Commission International del׳Eclairage (CIE) chromaticity coordinates of Li6CaLa2Ta2O12:0.5Eu3+ and Li6CaLa2Sb2O12:0.4Eu3+ phosphors are (0.65, 0.34) and (0.64, 0.35), respectively, which are very close to the standard of National Television System Committee (NTSC) (x=0.67, y=0.33).