水热法合成蓝宝石的化学成分及光谱学表征

蓝宝石作为五大名贵宝石之一，经济价值极高，其中“皇家蓝”、“矢车菊蓝”最为昂贵。而水热法可合成出颜色与“皇家蓝”色极为相似的蓝宝石，且合成出的晶体较大，可通过切磨加工获得内部纯净的样品，仅凭外观及常规方法难以鉴别。选取了7颗水热法合成蓝色蓝宝石为实验对象，采用LA-ICP-MS、拉曼光谱仪、红外光谱仪、紫外-可见分光光度计和三维荧光光谱仪，对其化学成分、谱学特征进行研究，并与外观极为相似的天然蓝宝石、焰熔法合成蓝宝石进行对比分析。分析表明，水热法合成蓝宝石总体成分较为单一，而天然蓝宝石则含有丰富的微量元素。三种样品拉曼光谱均呈现典型的刚玉振动模式，显示A_1g和E_g振动模的拉曼峰。在红外光谱的指纹区，三种样品的吸收峰均无明显差别，与拉曼光谱的结果耦合。但在官能团区3 000～4 000 cm^-1波数范围，水热法合成蓝宝石存在由含水矿物包裹体产生的羟基振动峰，而天然蓝宝石和焰熔法合成蓝宝石未显示此特征。紫外-可见光谱表明三种样品均为Fe²⁺-Ti⁴⁺对致色，但水热法与焰熔法合成蓝宝...

Chemical Composition and Spectra Characteristics of Hydrothermal Synthetic Sapphire

Sapphires has high economic value as one of the five precious stones. Among them, “royal blue” and “bonnet blue” are the most expensive. Using the hydrothermal method can synthesize “royal blue” sapphires, and the synthesized crystal is large and can have a pure interior by cutting and grinding, so it is difficult to identify it only by appearance and conventional methods. The researchers select seven blue hydrothermal synthetic sapphires to analyze their chemical composition and spectra features by LA-ICP-MS, Raman spectrometer, Infrared spectrometer, UV-Vis absorption spectrometer and Three-dimensional Fluorescence spectrometers. These samples are compared to natural and flame-fusion synthetic sapphires with a similar appearance. The analysis shows that the chemical compositions of hydrothermal synthetic sapphires are simple, but natural sapphire usually contains rich trace elements. In Raman spectra, three kinds of sapphires samples all show typical corundum vibration modes with A_1g and E_g. In the lattice vibration region of Infrared spectra, there is no obvious difference, which fits the result of Raman spectra. However, in the 3 000～4 000 cm-1 region of Infrared spectra, hydrothermal synthetic sapphires show the hydroxide radical vibrations generated by hydrated mineral inclusion, but it isn’t displayed in natural and flame-fusion synthetic sapphires. UV-Vis spectra show that Fe2+-Ti4+ ion pairs produce colors in these three kinds of samples, but hydrothermal and flame-fusion synthetic sapphires lack the 450nm absorption peak of the natural sapphire. 3D fluorescence spectra show that both hydrothermal and flame-fusion synthetic sapphires have blue fluorescence induced by Ti4+ ion-related charge transfer under the excitation of a 240nm light source, which is lacking in natural sapphire. Nevertheless, there is no such fluorescence in the natural sapphire. To conclude, chemical composition, Infrared spectra, UV-Vis absorption spectra, and 3D Fluorescence spectra can provide important evidence for identifying hydrothermal synthetic sapphires.