Gemmological Characteristics Of Synthetic Moissanite And Preliminary Study On Film Covering Experiment

The chemical composition of synthetic moissanite is Si C,which is the third generation semiconductor material.At the same time,it is active in the jewelry market as a high-quality diamond imitation,and is a gem material with good application prospects.In order to enrich the gemological characteristics of synthetic moissanite,this article uses gem microscope,infrared spectrometer,ultraviolet-visible spectrophotometer,micro-Raman spectrometer,laser induced breakdown spectrometer and other instruments to summarize the general gemological characteristics,color genesis and characteristics of spectrum.In addition,the near colorless synthetic moissanite coated with diamond film by plasma chemical vapor deposition?MPCVD?was systematically tested and its identification characteristics were preliminarily discussed.Synthetic moissanite is rich in color,including colorless,light brown yellow,bro-wn,green,blue-green and green-blue.Medium-strong red or green fluorescence can be seen under long wave,weak to moderate red or green fluorescence can be seen under short wave,and weak-strong red phosphorescence can be seen.The inclusions are abundant,with obvious rear facet edge ghosts,white tubular inclusions,nail-shaped inclusions and crystal inclusions.UV-Vis absorption spectrum and composition analysis show that the samples with blue and green tones contain n-type doping element N and p-type doping element Al,and the absorption spectrum has two absorption bands at 464nm and 585-590nm.The 464nm absorption band is attributed to the electron transition from the shallow donor energy level introduced by N to conduction band,and the 585?590nm absorption band is attributed to the electron transition from the valence band to the Al acceptor impurity.The absorption peak of the infrared reflection spectrum is attributed to the anti-symmetric stretching vibration of the Si-C bond,and the strong"reststrahlen reflection band"is visible between 700cm^-1 and1000cm^-1.According to Raman spectroscopy,the polytype structure of synthetic moissanite can be determined.The samples are mainly 4H-Si C,and a few are 6H-Si C;the samples with uneven colors can exhibit a multi-type mixed structure,the main polytype region is 4H type,and the minor polytype region is 15R or 6H type,and the minor polytype region corresponds to the dark green part doped with a higher concentration.It is inferred that the higher doping concentration affects the stability of the polytype,resulting in a multi-type mixed structure.The MPCVD method was used to grow a diamond coating experiment on the surface of the synthetic moissanite.The results showed that some of the coated samples showed obvious coating traces,and it displays blue fluorescence similar to CVD synthetic diamond under Diamond View^TM.The"reststrahlen reflection band"in the infrared reflection spectrum is distorted.Diamond particles,spherical particles,layered irregular particles and densely distributed cone-shaped growth structure can be seen on the membrane surface.The carbon-to-silicon atomic ratio on the surface of the coated sample is about 1.86,which is abnormally higher than the carbon-to-silicon ratio of moissanite,which indicates the presence of extra C on the surface of the coated sample.