CVD合成钻石的层状生长结构和紫外荧光特征

Characteristics of Lamellar Growth Structure and Ultraviolet Fluorescence of CVD Synthetic Diamonds

最近NGTC实验室检测出多批次CVD合成钻石,这些CVD合成钻石均具有明显的鉴定特征,使用钻石观测仪(DiamondViewTM)观察可见蓝色、橙红色荧光和蓝色磷光以及细密层状生长纹理,光致发光光谱中可见737nm处的特征发光线。这些特征均与其生长结构及生长过程中进入钻石晶体中的杂质有关。笔者以最近检测过程中发现的一颗CVD合成钻石为例,使用高倍率显微技术对其层状结构的微细特征及其在钻石观测仪下的荧光特征的关系进行了详细观察和对比。结果显示,此样品与之前检测到的CVD合成钻石略有差异。此次检测到的样品在钻石观测仪(DiamondViewTM)下观察具有较宽的层状生长分区,层与层之间的分界线十分明显且在高倍显微镜下也可见到细微的生长特征。通过对样品特征的分析,了解了晶体生长过程中多阶段生长条件的变化,更直观的展现了CVD合成钻石的生长过程。

Recently, several batches of CVD synthetic diamonds have been detected in NGTC laboratory. Identification characteristics of these CVD synthetic diamonds are obvious. Blue and orangy red fluorescence, blue phosphorescence and fine lamellar growth structure can be observed under DiamondViewTM and characteristic line at 737 nm can be seen in the photolu- minescence spectroscopy. These characteristics result from the growth conditions and mech- anism. In this article, we took a CVD synthetic diamond found recently as an example, and reported the differences in the identification characteristics from the CVD synthetic diamonds tested before. The surface and internal characteristics of the sample were examined by using gemmological microscope and differential interference microscope. Fluorescence and phos- phorescence of the CVD synthetic diamond were observed under 254 nm （short wave） and 365 nm （long wave） ultraviolet radiation excitation, and UV fluorescence characteristics un-der DiamondViewTM （230 nm） were studied. Infrared absorption spectra of the sample were recorded, covering the mid-infrared spectral range （6 000~400 cm-1 , 2 cm-1 resolu- tion） and near infrared spectral range （12 000~4 000 cm 1, 4 cm 1resolution） at room tem- perature with the help of a Nicolet 6 700 Fourier transform infrared spectrometer. We recor- ded photoluminescence spectra of the diamond at the temperature of liquid nitrogen, using a Renishaw 2000 system with a 514.5 nm Arion laser as the light source. It was also found that this sample displayed subtle layer growth characteristics and abnormal interference col- ours. Typical wide lamellar growth structures can be observed under DiamondViewTM. Boundary between layers is significantly clear, which can be seen under a gemmological mi- croscope. The lamellar growth structures resulted from the variations of growth conditions and the discontinuous crystal growth during the processes. The discontinuity of the growth could lead to the dark carbon components with sp2 bonds on the （100） growing surface. Ab- sorption lines at 7 354, 6 856, 5 563 cm^-1 concerned with hydrogen can be seen in the near infrared and mid-infrared spectra. It was reported that 8 753, 7 354, 6 856, 6 425, 5 563, 3 123 cm 1 peaks were detected in the NIR spectra in the CVD diamonds produced by American A- pollo company, and those absorption peaks have been assigned to hydrogen impurity in the CVD synthetic diamonds, which were not found in the natural diamonds. After the high pressure and high temperature treatment, those absorption peaks would disappear, which in- dicate the sample has not undergone the HTHP treatment. In the photoluminescence spec- tra, N--V centers spectral lines located at 575, 637 nm and double lines of Si--V centers lo- cated at 737 nm can be seen. The double lines at 737 nm are a strong proof of CVD dia- monds. Through the analysis of characteristics of the sample, it was understood that the CVD synthetic diamond grow in the multiple growth stages where the growth conditions could be slightly different. In a conclusion, the sample is considered as a CVD diamond prod- uct of early stage and has not undergone the HTHP treatment.