掺铈YVO_4晶体的发光特性及铈离子的价态分析

Spectroscopic properties of cerium doped YVO_4 crystals and analysis on valence state of cerium ion

采用中频感应单晶炉和提拉法生长了高质量的掺Ce的YVO4晶体,并采用了两种不同的方式进行掺杂,即分别在YVO4晶体掺入了Ce2(CO3)3和CeO2,两种不同方式的掺杂浓度均为2at%.使用XRD测试了这两种晶体的物相,发现样品主要以YVO4相存在.吸收谱、荧光光谱和激发光谱的测试发现,这两种不同掺杂方式所得到的样品具有相似的光谱特性,即使用325nm的紫外线激发时,两种样品均可发出以440nm为中心的宽带蓝光,这是来自Ce3+离子的5d→4f的特征发射;而在460nm的激发下,两种样品又均可发出以620nm为中心的宽带红光.通过X射线光电子能谱(XPS)对样品中的各个元素进行的测试分析,发现氧元素的1s峰分裂为529.8eV和531.8eV,这说明晶体中存在两种配位氧离子,一种是正常配位的氧离子(O2),另一种是带空穴的配位氧离子(O).由Ce的XPS测试结果中展现的5个5d峰推断,样品中的铈是以Ce3+和Ce4+两种形式共存,这种共存与两种配位氧离子的存在密切相关.我们认为,Ce:YVO4晶体的宽带红光发射来自Ce4+-O2的电荷迁移发光,并且它有可能因此而成为一种新型的用于白光LED的红色荧光粉.

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 Cea＋ 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 Ce2＋ 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.