Preparation of Gd2O3:Er,Yb Nanoparticles by Laser Ablation in Liquid and Their Optical Properties for Biomedical Application

Gd2O3:Er,Yb upconversion nanoparticles were obtained by laser ablation in liquid, and their optical properties were investigated. These nanoparticles are suitable for photodynamic therapy which is a cancer treatment approach. Since the nanoparticles are for medical use, purity is required. Thus, laser ablation in liquid was selected as a suitable production method because it produces no impurities. Nanoparticles were prepared by Nd:YAG (532-nm) laser-irradiation to Gd2O3:Er,Yb target in water. The nanoparticles' compositions were analyzed using X-ray diffraction, which showed that the nanoparticles and target raw material have the same peak. The primary particle size was measured using scanning electron microscopy, which revealed the coarse ( 100 nm) and fine (<100 nm) nanoparticles. The secondary particle size was investigated by dynamic light-scattering, which indicated the aggregation of fine nanoparticles. Upconversion luminescence and photon number were measured using a photoluminescence spectrometer with 980-nm laser excitation. Visible light was obtained due to upconversion. The photoluminescence intensity increased until the middle fluence and slightly decreased at the high fluence. Besides, the photon number was increased from 2.3 to 3.2. It is considered that nonradiative deactivation of fine nanoparticles affected the emission characteristics and photon number.