YPO4 nanocrystals: preparation and size-induced lattice symmetry enhancement

YPO4 and Eu doped YPO4 nanocrystals were prepared via a simple hydrothermal method. The phase purity, microstructure, surface absorbed water and luminescence properties were characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), fluorescence spectrum, infrared spectroscopy, Raman spectroscopy and thermogravimetry analysis(TGA). Combined with XRD and TEM analysis, it was found that YPO4 nanocrystals crystallized into a single phase of tetragonal (I41/amd) zircon structure. YPO4 nanocrystals showed a size reduction with the reaction temperature decreasing. Considering the XRD, IR and Raman results, a lattice expansion and the unit cell symmetry enhancement were observed with the particle size decreasing. A dipole to dipole interaction model was applied to investigate the relationship of the variation of microstructure and the particle size. The emission spectrum of Eu doped YPO4 nanocrystals was also presented and the emission bands were clearly ascribed to the f to f transitions of Eu3+.