Luminescent Properties of Tb3+-Doped NaCaPO4 Phosphor

Trivalent-terbiun-doped NaCaPO4 powder phosphors were prepared with different processes by using a conventional solid state reaction method. The phase and the structure of the as-prepared samples were characterized by using X-ray diffraction. The excitation and the emission spectra were measured to characterize the luminescent properties of the NaCaPO4:Tb3+ phosphors. The excitation spectrum exhibited one strong band located in the UV region at 274 nm and was assigned to 4f(8) --> 4f(7)5d(1) transition, and sonic other excitation bands in the longer wavelength region were attributed to the f-f transitions within the Tb3+ (4f(8)) configuration. The emission spectra were measured upon 370-nm excitation, and the most intense peak was observed in the green region at 547 nm, corresponding to the D-5(4) --> F-7(5) transition. The emitting color of Tb3+-doped NaCaPO4 phosphor is discussed based on the CIE diagram. The lifetime of the D-5(4) energy level of Tb3+ ions in the NaCaPO4 phosphor was measured upon 355-nm excitation. From this study, we have successfully optimized the preparation and emission process of the Tb-doped NaCaPO4 green phosphor for use in white-light-emitting diodes.