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

Sr_0.85−x Ca _x MoO₄:Eu _0.15 ³⁺ (0.15 ≤ x ≤ 0.45) and Sr_0.6Ca_0.25(Mo_1−y Si _y )O₄:Eu _0.15 ³⁺ (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 Sr_0.85−x Ca _x MoO₄:Eu _0.15 ³⁺ and Sr_0.6Ca_0.25(Mo_1−y Si _y )O₄:Eu _0.15 ³⁺ 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 Sr_0.85−x Ca _x (Mo_1−y Si _y )O₄:Eu _0.15 ³⁺ with various concentration of Ca²⁺ and Si⁴⁺ were investigated in detail. The results indicate that Sr_0.85−x Ca _x MoO₄:Eu _0.15 ³⁺ and Sr_0.6Ca_0.25(Mo_1−y Si _y )O₄:Eu _0.15 ³⁺ 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 Sr_0.85−x Ca _x MoO₄:Eu _0.15 ³⁺ , the emission intensity of Sr_0.6Ca_0.25(Mo_1−y Si _y )O₄:Eu _0.15 ³⁺ 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 Sr_0.85−x Ca _x (Mo_1−y Si _y )O₄:Eu _0.15 ³⁺ 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 Sr_0.85−x Ca _x (Mo_1−y Si _y )O₄:Eu _0.15 ³⁺ is an efficient red emitting phosphor for white LED applications.