Spectroscopic properties of cerium doped YVO4 crystals and analysis on valence state of cerium ion

High-quality cerium doped YVO4 crystals are grown by the Czochralski method in a furnace heated by medium frequency induction. Cerium carbonate and ceria of 2 at% are respectively doped into the different crystals. The X-ray diffraction spectra show that all samples present YVO4 crystallographic phase. The absorption spectra, excitation spectra and photoluminescence spectra of the samples are measured. It is found that the spectroscopic properties of the samples doped with the different cerium impurities are similar. The two kinds of the samples each radiate a wideband blue light centered at 440 nm when excited by 325 nm light. This blue light emission is due to the 5d → 4f intrinsic emission of Ce3+ ions. In addition, the two kinds of the samples each radiate a wideband red light centered at 620 nm when excited by 460 nm light. The X-ray photoelectron spectroscopy (XPS) show that the O(1s) peak splits into two peaks at 529.8 eV and 531.8 eV, which indicate that there are two types of coordinate oxygen ions in the crystal. One kind of coordinate oxygen ion is normal coordinated oxygen ion (O2-) and another kind of coordinate oxygen ion is a hole (O-). According to recorded 5 peaks of Ce(3d) XPS, it is deduced that the Ce3+ ions and Ce4+ ions coexist in each of these samples. It is considered that the wideband red light emission of Ce:YVO4 crystal is due to the charge transfer transition of the Ce4+-O2- ion pairs, and Ce:YVO4 powders may become a novel red phosphor used for white LED.