Influence of citrate on phase transformation and photoluminescence properties in LaPO4 and LaPO4:Eu

Abstract

The hexagonal and monoclinic phase LaPO₄ and LaPO₄:Eu nanostructures have been controllably synthesized by a citrate-induced hydrothermal process at 100 °C. The crystal growth of LaPO₄ nanostructures was investigated, and the phase transformation of nanostructured LaPO₄ 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 LaPO₄ transformed into the monoclinic phase. High concentrations of citrate would lead to the formation of hexagonal phase LaPO₄. The photoluminescence properties of the monoclinic phase LaPO₄:Eu prepared using a citrate-induced process demonstrate that the electric dipole transition (⁵D₀ → ⁷F₂) is stronger than the magnetic dipole transition (⁵D₀ → ⁷F₁), which indicated that Eu³⁺ is in a site with no inversion center. The strongest emission peak of hexagonal phase LaPO₄:Eu comes from ⁵D₀ → ⁷F₁. Furthermore, the citrate-induced hexagonal phase LaPO₄:Eu has a stronger emission intensity than the hexagonal phase LaPO₄:Eu prepared not using a citrate-induced process.