Preparation and structure of NaREO2 (RE=Lu，Y)

Abstract

NaLuO2 and NaYO2 powder crystals were prepared by the conventional solid state reaction method. It is more difficult to synthesize pure NaLuO2 powder crystals than NaYO2. To monitor the quantity of Lu2O3 in the NaLuO2 sample, we calculated the relation between weight ratio and XRD peak absolute intensity ratio of Lu2O3 to NaLuO2 by X-ray diffraction method, and obtained the constant (kLu2O3NaLuO2=3.8). Pure NaLuO2 powder crystals were obtained by optimizing reaction conditions (sintering temperature, reaction time, raw material molar ratio and fluxes) in a two-step method. The best reaction condition was found to be that the mixture of Na2O2, Lu2O3 and Na3PO4 at a molar ratio of 200∶100∶7 is filled into a small inner ceramic crucible which is placed inside a larger outer ceramic crucible and sintered at 850℃ for 3 h. The sample has pure hexagonal structure (space group R3m, lattice constant a＝0.3335 nm, c＝1.6545 nm). XRD pattern of NaLuO2 in this experiment indicated that there is an additional diffraction peak (006) compared with JCPDS23-0684, and the labeled (007), (111) and (117) peaks should be corrected to (104), (110) and (024) according to the Bragg reflection conditions of hexagonal system. Eu3+ doped NaLuO2 and NaYO2 have different emission spectra, which indicates that Eu3+ occupy different symmetric sites. The main peak of the former (having inversion centre i) is at about 590nm, corresponding to the magnetic dipole transition of Eu3+ (5D0→7F1), and the later (no inversion centre i) is at about 610nm, corresponding to the electric dipole transition of Eu3+ (5D0→7F2).