PHOTOLUMINESCENT MATERIALS BASED ON EU~(2+) DOPED ALKALINE EARTH HALIDE PHOSPHATES

摘要

The X-ray diffractograms of the mixed crystals show the characteristic reflections of the hexagonal apatite structure. The space group of the materials is P6_3/m. There are two crystallographically different sites for the cations in the unit cell, the 4f and the 6h Wyckoff positions. Eu~(2+) ions occupy preferentially the 6h cation positions. The luminescence of the samples arises from transitions between 4f~65d~1 and 4f~7 configurations of the Eu~(2+) ion. It depends strongly on the composition of the polycrystalline materials, and there are significant differences in the optical properties of the Eu~(2+) ion between the four systems given above. The emission band of the starting material, Sr_(4.99)Eu_(0.01)(PO_4)_3Cl , appears in the spectral region between 19000 and 25000 cm~1 with a band width at half height of 1728 cm~(-1). The maximum lies at 22463 cm~(-1) (Fig. 1). Mixed crystals of the composition Sr_5 _(-y)Eu_y(PO_4)_3Cl_(1-x)Br_x show the most intensive emission (Fig. 1). The optical properties are discussed in connection with the composition and the structure parameters of the polycrystalline materials.