Nd<sub>3</sub>PO<sub>7</sub> was synthesized by solid state reaction techniques under high temperature in air atmosphere for the first time, the crystal phase of Nd<sub>3</sub>PO<sub>7</sub> was investigated by X-ray powder diffraction and scanning electron microscopy, the results show that Nd<sub>3</sub>PO<sub>7</sub> is monoclinic phase; the Nd: P: O = 3:1:7; Infrared spectroscopic study was used to obtain further structural information about the nature of bonding in Nd<sub>3</sub>PO<sub>7</sub>. Emission spectra of Nd<sub>3</sub>PO<sub>7</sub> were investigated at room temperature using a fluorescence spectrometer in the visible portion of the spectrum. Excellent emission was observed at 441 nm when Nd<sub>3</sub>PO<sub>7</sub> excited at 325 nm wavelength, which was assigned to the <sup>4</sup>G<sub>11/2</sub>-<sup>4</sup>I<sub>9/2</sub> transition of Nd<sup>3+</sup> ions. All the investigated suggestions that Nd<sub>3</sub>PO<sub>7</sub> is a good phosphor candidate applied in fluorescent materials.
In this paper, La<sub>x</sub>Nd<sub>1-x</sub>PO<sub>4</sub>(x=0, 0.5, 0.8) series crystals with high Nd-concentration were grown through a seed-inducing method using Li<sub>2</sub>CO<sub>3</sub>-2MoO<sub>3</sub> as a flux, and some factors influencing the quality of crystals were also discussed. The IR, absorption and fluorescence spectra of La<sub>0.5</sub>Nd<sub>0.5</sub>PO<sub>4</sub> crystals at room temperature were measured. High temperature X-ray diffraction was conducted to investigate the thermal expansion behavior of NdPO<sub>4</sub> crystals in the temperature range from 25°C to 900°C. Abnormal diffraction peaks shifts were observed along the (200) and (020) direction. The results indicate that as temperature increased, the crystal in the (200) and (020) direction contracted (from 25 °C to 700 °C) at first, and then expanded (from 700°C to 900°C). The mechanism responsible for the abnormal thermal expansion in NdPO<sub>4</sub> was attributed to the existence of rigid unit modes (RUM).