水平定向结晶法(HOC法)合成变石的宝石学及谱学特征

Gemmological and Spectroscopic Characteristics of Synthetic Alexandrite by the Horizontally Oriented Crystallisation Method

目前市场上合成变石中以提拉法合成产品为主,水平定向结晶法(HOC法)合成变石产品相对少见,其宝石学与谱学特征的研究资料仍有待补充。本文选择8颗来自俄罗斯厂家的HOC法合成变石样品为研究对象,采用折射仪等常规宝石学仪器、激光剥蚀电感耦合等离子体质谱仪、能量型色散X射线荧光能谱仪、紫外-可见光光谱仪、荧光光谱仪、拉曼光谱仪和傅里叶变换红外光谱仪对该类样品进行测试分析,探究其包裹体特征,微量元素组成、红外光谱、紫外-可见光光谱和荧光光谱等特征及与天然变石的差异。放大观察结果显示,HOC法合成变石样品的典型内含物为大量定向拉长空洞以及簇状金属包裹体。化学成分测试显示含有致色元素Cr和V,Cr含量较天然变石偏高;Fe元素含量极低,Mg、Ti、Ga等元素含量较天然变石低,且具有异常高的Mo含量,推测为金属Mo坩埚残余所致。紫外-可见光光谱仪测试结果显示为典型Cr谱,在橙黄光区与紫光区有两个宽的吸收带,645、656 nm处具有肩峰,680 nm处具有弱吸收峰。三维荧光光谱显示HOC法合成变石具有678、680 nm处强荧光峰以及690、696 nm处弱荧光峰,均为Cr元素所致,不具有天然变石中Ti和O元素的配合物所致460~550 nm处的发光中心。红外吸收光谱显示不具有天然变石特有的2160、2402 cm^(-1)处吸收峰以及3000~3500 cm^(-1)范围内与水有关的吸收。

Cumently,the market is dominated by synthetic alexandrite synthesized by the czochralski method,while the synthetic alexandrite synthesized by the Horizontally Oriented Crystallisation(HOC)method is relatively rare,and the study of its gemmological and spectroscopic characteristics still needs to be supplemented.In this paper,8 synthetic alexandrite by HOC method from a Russian manufacturer were selected as the research objects and tested and analyzed using conventional gemmological instruments such as refractometers,laser-ablation inductively coupled plasma mass spectrometer(LA-ICP-MS),energy dispersive X-ray fluorescence spectrometer(EDXRF),UV-Vis spectrometer,fluorescence spectrometer,Raman spectrometer,and Fourier transform infrared(FTIR)spectrometer,to explore its inclusion characteristics,trace elements compositions,infrared spectrum,UV-Vis spectrum,fluorescence spectrum,and other characteristics to dirstinguish it from natural alexandrite.The magnified observation results show that the typical inclusions of the synthetic alexandrite samples by HOC method are a large number of oriented elongated voids and clustered metal inclusions.Chemical composition tests show the presence of the colour-causing elements Cr and V.The Cr content is higher than that of natural alexandrite.Fe element content is very low;the content of Mg,Ti,Ga and other elements are lower than the natural alexandrite,with unusual high Mo content,presumably due to the Mo crucible residue.UV-Vis spectrometer test results show a typical chromium spectrum,with two broad absorption bands in the orange-yellow and violet regions,shoulder peaks at 645 nm and 656 nm,and a weak absorption peak at 680 nm.Three-dimensional fluorescence test concluded that HOC method synthetic alexandrite has strong fluorescence peaks at 678 nm and 680 nm,and weak fluorescence peaks at 690 nm and 696 nm,which are all caused by Cr element,and does not have the luminescence center at 460-550 nm caused by Ti and O element in natural alexandrite.The infrared absorption spectrum shows that it does not have the absorption peaks at 2160 cm^(-1)and 2402 cm^(-1),which are unique to natural alexandrite,and there is no obvious water related absorption between 3000-3500 cm^(-1).