Crystal and band structures, and optical characterizations of sodium rare earth phosphates NaLnP2O7 and NaLn(PO3)4 (Ln = Ce, Eu)

Sodium rare earth diphosphates NaLnP2O7 (Ln = Ce (1), Eu (2)) and polyphosphates NaLn(PO3)4 (Ln = Ce (3), Eu (4)) have been synthesized by the high temperature solution reaction. These compounds have been characterized by means of single-crystal X-ray diffraction, elemental analyses, spectral measurements, and theoretical computations. Their structural characteristics are described, and the differences among them are compared. The nature of chemical bonds and electronic origins of optical transitions are analyzed for 1 and 3 in terms of crystal band structures, density of states (DOS), and optical response functions which have been calculated by the DFT method. Results of spectral measurements indicate that crystals 1 and 3 may become promising hosts for ultraviolet-emitting solid-state light sources, and crystals 2 and 4 exhibit the characteristic yellow–red light emission under the excitation of ultraviolet light.