“…Considering the environmental protection, the fluorides based phosphors cannot be widely used for the potential toxicity of fluorine-containing species. Consequently, oxide/complex oxides based phosphors have also been studied in parallel with fluoride based phosphors for their potential applications in lighting and display in consideration of their excellent stability and low toxicity [5,6,9,10,12,18]. Double molybdates and tungstates ALn(MO 4 ) 2 (A = alkali metal ions; Ln = trivalent rare earth ions; M = Mo, W) with scheelite (CaWO 4 ) structure are efficient luminescent hosts [19][20][21] and no concentration quenching occurred in these compounds [22,23].…”