Enhanced luminescence of a Eu3+-activated double perovskite (Na, Li)LaMgWO6 phosphor based on A site inducing energy transfer

Li+ ion substituted Na1−xLixLa0.95Eu0.05MgWO6 phosphors were successfully synthesized by an improved sol-gel method using citric acid and polyethylene glycol as complexing agents. The structural evolution was systematically investigated by X-ray diffraction with Rietveld structure refinement and Raman spectra. The layered ordering of A-site cations and a second-order Jahn-Teller distortion of B' cations simultaneously existed in this double perovskite. The decreased symmetry and lattice parameters within the same space group C2/m were observed from the Li+ substituted powders. Upon increasing the Li+ concentration, the absorption intensities of the 4f−4f transitions of Eu3+ monotonically increased. Likewise, the intensity of 5D0-7F2 monotonically increased under the excitations of both near-ultraviolet and blue light, with an enhancement of ten- and six-fold, respectively. The relative intensity ratio of red/orange emissions gradually increased, and the CIE chromaticity coordinates gradually approached those of standard red light. "A site inducing energy transfer" in double perovskite was achieved by selecting a substitution element with a small radius.