Excellent red phosphors of double perovskite Ca2LaMO6:Eu (M=Sb, Nb, Ta) with distorted coordination environment

Double perovskite Ca2LaSbO6, successfully synthesized by solid state reaction method, was identified by Rietveld refinements to crystallize in the monoclinic space group P21/n, which is isostructural to Ca2LaMO6 (M=Nb, Ta). Excellent red luminescence of Eu-doped Ca2LaMO6 (M=Sb, Nb, Ta) can be obtained and no luminescence quenching effect was observed when Eu-doping level reached 40%. For Ca2La0.6NbO6:0.4Eu3+, quantum efficiencies of 20.9% and 27.7% were reached to show high light conversion and bright red emission excited at 465 nm (blue light) and 534 nm (green light), respectively, comparable to the commercial phosphors. Through systemic investigation for the series of double perovskite compounds, the excellent red emission in Ca2LaMO6 is attributed to highly distorted polyhedra of EuO8 (low tolerance factor of the pervoskite), and large bond distances of La−O (low crystal field effect of the activator).