Crystal structure and luminescent properties of Li+ ions doped double tungstate KEu(WO4)2 red emitting phosphors

Li+ ions doped double tungstate KEu(WO4)(2) phosphors were prepared by using sol-gel method. The crystal structure and luminescence properties of K1-xLixEu(WO4)(2) (0 <= x <= 0.5) were characterized by means of X-ray diffraction (XRD) Rietveld refinement, photoluminescence and absorption spectra. The results show that the addition of Li+ ions can change the lattice parameters, Eu-0 and W-0 bond distance of K1-xLixEu(WO4)(2). The phosphors consist of K1-xLixEu(WO4)(2) and LiEu(WO4)(2) phase as the concentration of Li+ is over 0.2 and the volume fraction of LiEu(WO4)(2) increase with increase of Li+ ions concentration. The dopant of Li+ in KEu(WO4)(2) obviously enhance band gap energy. Under excitation at 393 nm, K0.7Li0.3Eu(WO4)(2) phosphor exhibits strongest red emitting light at 615 nm from D-5(0) -> F-7(2) transition of Eu3+ ions. K0.7Li0.3Eu(WO4)(2) phosphor shows higher thermal activation energy than that of KEu(WO4)(2) phosphors, better thermal stability, the long lifetime value and better internal quantum efficiency.