Luminescence properties of Ca2+ and Si4+ co-doped strontium molybdate red phosphors for white LEDs

Abstract

Sr0.85−xCaxMoO4:Eu0.153+ (0.15 ≤ x ≤ 0.45) and Sr0.6Ca0.25(Mo1−ySiy)O4:Eu0.153+ (0 ≤ y ≤ 0.08) red phosphors materials for white LEDs were synthesized by the high temperature solid state reaction. The properties were characterized by means of X-ray diffraction (XRD) and photoluminescence spectra. The XRD pattern shows that the Sr0.85−xCaxMoO4:Eu0.153+ and Sr0.6Ca0.25(Mo1−ySiy)O4:Eu0.153+ phosphors sintered at 800 °C for 5 h are SrMoO4 phase. And the samples are crystallized well with the scheelite structure. The luminescent properties of Sr0.85−xCax(Mo1−ySiy)O4:Eu0.153+ with various concentration of Ca2+ and Si4+ were investigated in detail. The results indicate that Sr0.85−xCaxMoO4:Eu0.153+ and Sr0.6Ca0.25(Mo1−ySiy)O4:Eu0.153+ phosphors can be excited by 394 and 464 nm lights and their light emitting properties were improved by co-doping Si4+ and Ca2+ ions. The emission spectra exhibit the most intense emission at 611 and 615 nm, and the latter is corresponding to the 5D0 → 7F2 transition of the Eu3+. Compared with Sr0.85−xCaxMoO4:Eu0.153+, the emission intensity of Sr0.6Ca0.25(Mo1−ySiy)O4:Eu0.153+ is increased obviously. It is found that appropriate Ca2+ and Si4+ concentration can enhance the luminescent intensity and improve crystallization, and the highest emission intensity on the 615 nm is exhibited when x = 0.25 and y = 0.05. Moreover, the CIE chromaticity (x, y) of Sr0.85−xCax(Mo1−ySiy)O4:Eu0.153+ excited by 394 nm light are analyzed. When the doping x of Ca2+ is 0.02 and y of Si4+ is 0.05, phosphors of the samples turn from pink to red. These results present that the Sr0.85−xCax(Mo1−ySiy)O4:Eu0.153+ is an efficient red emitting phosphor for white LED applications.