Luminescence enhancement in red-emitting MgMoO${}_4$:Eu${}^{3+}$ phosphor by partially combined substitution of Mg${}^{2+}$-Mo${}^{6+}$-O${}^{2-}$ with Ca${}^{2+}$-W${}^{6+}$-F${}^{-}$

A serial of red-emitting MgMoO${}_4$: Eu${}^{3+}$ phosphors were synthesized via a high-temperature solid-phase approach. The effect of partially combined substitution of Mg${}^{2+}$-Mo${}^{6+}$-O${}^{2-}$ with Ca${}^{2+}$-W${}^{6+}$-F${}^{-}$ on the structure and luminescent properties of the MgMoO${}_4$: Eu${}^{3+}$ phosphor was thoroughly investigated. The crystal structure of the as-prepared MgMoO${}_4$: Eu${}^{3+}$ phosphor was not influenced by the partially combined Ca${}^{2+}$-W${}^{6+}$-F${}^{-}$ substitution. Under the excitation of 394 nm, The MgMoO${}_4$: Eu${}^{3+}$ phosphor could emit bright red light centered approximately at 612 nm, corresponding to the ${}^5$D${}_0$ → ${}^7$F${}_2$ transition of Eu${}^{3+}$ and the optimal concentration of Eu${}^{3+}$ was about x = 0.10. After the partially combined Ca${}^{2+}$-W${}^{6+}$-F${}^{-}$ substitution, the luminescence intensity of Eu${}^{3+}$ ions was approximately 1.94 times of the initial values owing to the alteration of the crystal field and charge compensation. The thermal stability of the partially substituted phosphor was significantly enhanced and the emission intensity at 423 K was approximately 82.3% of the initial value at room temperature. The internal quantum efficiency of the partially substituted sample is about 49.5%. A white light-emitting diode (LED) manufactured by the partially substituted red Mg${}_{0.7}$Ca${}_{0.2}$Mo${}_{0.8}$W${}_{0.2}$O${}_{3.8}$F${}_{0.2}$: 0.10Eu${}^{3+}$, combined with commercial blue-green phosphors and 395 nm chips exhibits high performance featuring CCT = 5441 K and Ra = 88.7. These results mean that the partially combined Ca${}^{2+}$-W${}^{6+}$-F${}^{-}$ substitution in MgMoO${}_4$: Eu${}^{3+}$ can be used to optimize luminescent properties of phosphors applied in white LEDs.