Hydrothermal syntheses and photoluminescence properties of rare-earth tungstate as near ultraviolet type red phosphors

Three families of scheelite CaWO4-based red luminescent phosphors, Ca1-1.5xWO4:xEu(3+) (0.02 <= x <= 0.09), Ca0.925-ySryWO4:0.05Eu(3+) (0 <= y <= 0.9) and Ca0.625Sr0.30W1-zMozO4:0.05Eu(3+) (0 <= z <= 0.7) were hydrothermally prepared and characterized. The substitutions of Sr2+ for Ca2+ and Mo6+ for W6+, which improve local symmetries surrounding Eu3+, assisted the energy transfer from O2- to Eu3+ in the process of optimizing the luminescence properties. The z = 0.2 members of Ca0.625Sr0.30W0.80Mo0.20O4:0.05Eu(3+) exhibited excellent bright red luminescence at 616 nm under near-UV excitation, narrowed emission spectra, room temperature luminescence lifetimes of milliseconds and maximum quantum efficiencies of 49%.