NaCaPO4: Eu (3+,2+) powdered phosphors were prepared by using wet and dry solid-state reaction methods, followed by heat treatment in different atmospheres (i.e., air, argon, oxygen, 10 % H2+90 % N2 gas), and the effect of sample preparation condition and heat treatment atmosphere on the -1028-NaCaPO4 Ó ü t| 9 \ ' ) a Eu (2+,3+) \ @ /ô Ç F g < AE& h $ í | 9î r] j ñ 1 p x -1029luminescent properties of the Eu 3+ or the Eu 2+ ions in the NaCaPO4 phosphors were studied. The NaCaPO4: Eu 3+ samples

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... repared by using the wet solid-state reaction method and then heat treated in air showed the strongest emission intensity of the Eu 3+ ions. To reduce the Eu 3+ to the Eu 2+ ion in NaCaPO4, we calcined the samples prepared in air and oxygen atmospheres again in a reducing atmosphere. Contrary to the emission intensity in NaCaPO4:Eu 3+ , the sample prepared by using the wet solid-state reaction method, followed by sintering in an oxygen atmosphere, showed the strongest emission intensity of the Eu 2+ ions. Unlike the usual oxide phosphors, the sample prepared by using the dry solid-state reaction method showed better emission efficiency than that prepared by using the wet solid-state reaction method for the NaCaPO4:Eu 3+ phosphors. The emission and the excitation spectra of the NaCaPO4:Eu 2+ phosphors exhibited a strong emission band in the wavelength region of 425-625 nm, with a peak at 507 nm, and an excitation band in the wavelength region of 275-500 nm, with a peak at 422 nm. We found that the optical and the luminescence properties of Eu 2+ /Eu 3+ doped in NaCaPO4 lattices to be highly dependent on the conditions of sample preparation and on the heat-treatment atmospheres.