Systematic studies on Ca19M2(PO4)14:Eu3+ (M = Mg, Zn) phosphors: Effects of M cation on photoluminescence

Ca19(1-x)M2(PO4)14:19xEu3+ (M = Mg, Zn) (x = 0.05, 0.07, 0.09, 0.10, 0.11 and 0.12) red phosphors were successfully synthesized by the high-temperature solid-phase reaction method. The phase composition, morphology and characteristic photoluminescence properties of Ca19Mg2(PO4)14 (CMPO):Eu3+ and Ca19Zn2(PO4)14 (CZPO):Eu3+ were analyzed by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM) and photoluminescence spectroscopy. The photoluminescence excitation (PLE) and emission (PL) spectra of both samples indicate that the phosphors can be effectively excited by ultraviolet (UV) and blue light, and also it is shown that the electric-dipole transition of Eu3+ is dominant. The typical concentration quenching occurs when Eu3+-doping concentrations of both phosphors exceed 10 mol%, and the PL intensity of CZPO:0.10Eu3+ sample is 1.65 times that of CMPO:0.10Eu3+. Furthermore, the infrared spectra (IR), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) curves, ultraviolet–visible diffuse reflectance spectra (UV–Vis DRS), thermal stability, chromaticity coordinates (CIE) and correlated color temperature (CCT) of Ca19M2(PO4)14:Eu3+ phosphors were evaluated in detail. The band gaps of CMPO and CZPO hosts were equal to 6.46 and 6.39 eV, respectively. The I423K/I298K values of CMPO:Eu3+ and CZPO:Eu3+ phosphors are as high as 73.89% and 88.29%. The chromaticity coordinates of Ca19(1-x)M2(PO4)14:19xEu3+ (M = Mg, Zn) phosphors locate in red region, and the color purity values of CMPO:Eu3+ and CZPO:Eu3+ are determined to be 99.82% and 99.61%, respectively. To sum up, the phosphors are considered as the potential luminescence materials for use in white light emitting diodes (w-LEDs).