高温高压处理对褐色CVD钻石谱学特征的影响

目前CVD法合成单晶钻石是超硬材料科学和宝石学关注的热点之一，该方法合成的单晶钻石常带有褐色调。通常采用高温高压法（HPHT）提高褐色CVD钻石的色级和透明度，在前期HPHT处理褐色CVD钻石实验基础上，选出颜色改善明显的三颗样品，对其处理前后谱学特征进行对比。采用紫外-可见吸收光谱、红外光谱、光致发光光谱、三维荧光光谱、激光拉曼光谱以及X射线摇摆曲线进行分析。结果表明，褐色和深褐色样品褪色温度较高，处理后样品紫外-可见吸收光谱吸收系数明显减小，透明度明显提高。样品中红外与近红外光谱显示，在1 332 cm-1处的吸收峰与N+中心有关，该中心是褐色CVD钻石常见特征。在3 124 cm-1处吸收峰与NVH0缺陷中心有关，该峰在CVD钻石和HPHT处理钻石中常见。另外在2 700~3 200 cm-1范围变化的一组吸收峰，与C-H键伸缩振动有关。高温对CVD钻石含H基团影响较大，在5~6 GPa压力下处理温度在1 500~1 700 ℃范围，会在近红外波段4 673，6 352，7 354，7 540，7 804和8 535 cm-1出现一组吸收峰，可指示样品经过较高温度处理。目前针对CVD钻石以及经过HPHT处理的CVD钻石近红外波段的论述较少，该研究可以为鉴定CVD钻石及HPHT处理CVD钻石提供依据。综合光致发光光谱和三维荧光光谱分析，处理后样品NV-缺陷比例减小，SiV-中心缺陷比例增加。在5~6 GPa压力下，仅当处理温度高于1 500 ℃时，样品三维荧光光谱在λ_ex/λ_em=500 nm/575 nm处荧光峰增强，在λ_ex/λ_em=490 nm/550 nm处荧光峰消失，从某种意义上该峰位变化可指示样品经过较高温度处理。物相分析结果显示，HPHT处理后CVD钻石在1 332 cm-1处拉曼位移半高宽和XRD摇摆曲线半高宽均减小，表现出了较好的一致性，说明经HPHT处理的褐色CVD钻石结晶质量变优。

Effects of Spectral Characteristics of High Temperature High Pressure Annealed Brown CVD Diamonds

Synthetic CVD single crystal diamond is one of the hot spot issues in superhard materials and gemology.Whereas most large single-crystal diamonds synthesized by CVD methods often come with a brown hue.CVD diamonds are often treated by the high temperature and high pressure(HPHT)method to improve the color and transparency.In this paper,based on the previous HPHT experiments,three samples with obvious positive effects are selected,utilizing a series of spectrum tests like UV-Vis absorption spectroscopy,infrared spectroscopy,photoluminescence spectroscopy,three-dimensional fluorescence spectroscopy,laser Raman spectroscopy and X-ray rocking curves to compare.Results indicated that brown and dark brown samples annealed at high temperatures work well.The absorption coefficient of the UV-Vis absorption spectrum of the sample decreases obviously,and transparency has improved significantly.Mid-infrared and near-infrared spectroscopy of CVD diamonds before and after HPHT-processing shows that the absorption peak at 1332 cm^-1 is related to the N⁺center,a common feature of CVD brown diamonds.The absorption peak at 3124 cm^-1 is related to the NVH₀ defect center,common in CVD diamonds and HPHT treated diamonds.Meanwhile,a set of absorption peaks at 2700~3200 cm^-1 was observed,associated with C—H stretching vibration.High temperature has a great influence on the H groups in CVD diamonds.After HPHT treatment at 5~6 GPa 1500~1700℃,in near-infrared band shows a set of absorption peaks at 4337,6352,7354,7540,7804 and 8535 cm^-1.Therefore,the appearance of these peaks can indicate that the sample has been treated at a high temperature.This study can provide bases for the identification of CVD diamonds,and HPHT treated CVD diamonds.The results of photoluminescence spectroscopy and three-dimensional fluorescence spectroscopy shows that the concentration of NV-center decreases while the concentration of SiV-center increases.Only when the temperature is above 1500℃at 5~6 GPa,thethree-dimensional fluorescence spectra of the samples were enhanced at λ_ex/λ_em=500 nm/575 nm while the fluorescence peak disappeared at λ_ex/λ_em=490 nm/550 nm.In a sense,the peak changes can indicate that the sample was treated at a high temperature.The phase analysis results show that the Raman shift FWHM at 1332 cm^-1 and XRD rocking curve FWHM decreases after HPHT-processing,which shows good consistency.The crystallization quality of brown CVD diamonds gets better after HPHT-processing.