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

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 DiamondView^TMand characteristic line at 737nm can be seen in the photoluminescence spectroscopy.These characteristics result from the growth conditions and mechanism.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 phosphorescence of the CVD synthetic diamond were observed under 254nm (short wave) and 365 nm (long wave) ultraviolet radiation excitation, and UV fluorescence characteristics under DiamondView^TM (<230nm) were studied.Infrared absorption spectra of the sample were recorded, covering the mid-infrared spectral range (6 000⁴00cm^-1, 2cm^-1 resolution) and near infrared spectral range (12 000⁴ 000cm^-1, 4cm^-1resolution) at room temperature with the help of a Nicolet 6 700Fourier transform infrared spectrometer.We recorded photoluminescence spectra of the diamond at the temperature of liquid nitrogen, using a Renishaw 2000system with a 514.5nm Arion laser as the light source.It was also found that this sample displayed subtle layer growth characteristics and abnormal interference colours.Typical wide lamellar growth structures can be observed under DiamondView^TM.Boundary between layers is significantly clear, which can be seen under a gemmological microscope.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.Absorption lines at 7 354, 6 856, 5 563cm^-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 123cm^-1 peaks were detected in the NIR spectra in the CVD diamonds produced by American Apollo 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 indicate the sample has not undergone the HTHP treatment.In the photoluminescence spectra, N-V centers spectral lines located at 575, 637nm and double lines of Si-V centers located at 737nm can be seen.The double lines at 737nm are a strong proof of CVD diamonds.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 product of early stage and has not undergone the HTHP treatment.