Preparation and Optical Properties of Trivalent Erbium-Doped CaY₂O₄ Powders Under 980 nm Excitation

Nanocrystalline CaY₂O₄:Er³⁺ up-conversion phosphor was prepared by the sol-gel process. A homogeneous precursor sol was heated on a hot plate and then coagulated gel was prefired at 300 °C for 4 hr in Ar, followed by final annealing at 1,200 °C for 4 h in Ar. The crystallinity of the powders after annealing was confirmed using an X-ray diffraction analysis. The shape and particle size of the powders were observed by field emission-scanning electron microscope and transmission electron microscope. Up-conversion luminescence spectra were recorded with a fluorescent spectrophotometer under a 980-nm excitation. The dependence of the up-converted intensities on pumping powers for powders was obtained by changing the excitation powers at room temperature. X-ray diffraction patterns confirmed the presence of single orthorhombic crystalline CaY₂O₄ and no impurity peaks were identified. Micrographical images of 3 mol%-doped CaY₂O₄ powder indicates that the particle size is uniform, and ranges from 100~200 nm. Up-conversion efficiency is the highest when the doping concentration of Er³⁺ is 3 mol%.