Influence of citrate on phase transformation and photoluminescence properties in LaPO(4) and LaPO(4):Eu

The hexagonal and monoclinic phase LaPO(4) and LaPO(4):Eu nanostructures have been controllably synthesized by a citrate-induced hydrothermal process at 100 °C. The crystal growth of LaPO(4) nanostructures was investigated, and the phase transformation of nanostructured LaPO(4) was systematically studied by varying the citrate concentration, pH value and reaction temperature. When 0.8 mmol of citrate was added into the reaction system, the hexagonal phase LaPO(4) transformed into the monoclinic phase. High concentrations of citrate would lead to the formation of hexagonal phase LaPO(4). The photoluminescence properties of the monoclinic phase LaPO(4):Eu prepared using a citrate-induced process demonstrate that the electric dipole transition ((5)D(0) → (7)F(2)) is stronger than the magnetic dipole transition ((5)D(0) → (7)F(1)), which indicated that Eu(3+) is in a site with no inversion center. The strongest emission peak of hexagonal phase LaPO(4):Eu comes from (5)D(0) → (7)F(1). Furthermore, the citrate-induced hexagonal phase LaPO(4):Eu has a stronger emission intensity than the hexagonal phase LaPO(4):Eu prepared not using a citrate-induced process.