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

Li⁺ ion substituted Na_1−xLi_xLa_0.95Eu_0.05MgWO₆ 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.