Hydrothermal synthesis and luminescence of Eu3+-doped Gd1–xLaxPO4 phosphates

Abstract

Eu3+-doped gadolinium, lanthanum and mixed gadolinium–lanthanum phosphates were synthesised by a hydrothermal method and investigated as luminescent phosphate materials. The target compositions included GdPO₄, LaPO₄ and Gd_1–xLa_xPO₄ doped with 15 mol% Eu³⁺; selected GdPO₄:Eu³⁺ samples were also prepared in the presence of sodium lauryl sulfate as a surfactant. X-ray diffraction showed the formation of hydrated phosphate phases. GdPO₄·H₂O:Eu³⁺ samples crystallised in a hexagonal hydrated phase, whereas increasing La content promoted mixtures of hexagonal and monoclinic phases. Photoluminescence measurements confirmed Eu3+-related excitation and emission transitions, with orange–red emission under near–UV excitation. The strongest emission was observed for GdPO₄·H₂O:Eu³⁺, while increasing surfactant content and increasing La substitution reduced emission intensity. Scanning electron microscopy revealed that agglomerated fine particles and partially elongated particles were formed. Thermal analysis indicated dehydration below approximately 500°C and suggested structural transformation at higher temperatures. The results show that hydrothermal synthesis yields luminescent Eu3+-doped hydrated phosphate materials, but further optimisation is required to obtain phase-pure monoclinic products and controlled morphology.