Preparation of Yb³⁺ doped GdPO₄ nanoparticles by solution-based processing

Yb³⁺ doped GdPO4 (GdPO4:Yb³⁺) nanoparticles are prepared in glycol solvent by autoclave treatment at 230 °C for 120 min. According to X-ray diffraction (XRD) patterns, the sample prepared in ethylene glycol is monazite-type GdPO4:Yb³⁺ without crystal water, while the sample prepared in 1,4-butanediol is rhabdophane-type GdPO4:Yb³⁺ with crystal water. The former shows more intense near infrared photoluminescence due to the f-f transition of Yb³⁺ in comparison with the latter. These results indicate that quenching of Yb³⁺ emission is attributed to energy dissipation due to the O-H vibration of crystal water. When the samples are prepared in ethylene glycol by autoclave treatment at 230 °C for different aging time, the crystallization degree estimated from integrated intensities of XRD peaks increases with increasing aging time. At the same time, the Yb³⁺ emission becomes strong. We found out that the photoluminescence intensity is linearly related with the crystallization degree.