Study On The Spectral Characteristics Of Natural And Synthetic Gemstones

The physical and chemical conditions of synthetic gemstones are simulated to natural gemstones.Artificial materials grown by artificial crystallization or recrystallization methody.Thus the identification of natural gemstones and synthetic gemstones becomes one of the most difficult gemological research.Paper mainly discusses the Raman spectroscopy of different gemstones,the difference of FWHM can provided new identification method for natural gems and synthetic gems.Using XRD,XRF,optical fiber spectrometer,RI and Raman spectrometer to test natural and synthetic gems,like alexandrite,crystal,spinel,opal.Main conclusions are as follows.Major chemical composition,crystal structures and the mechanism of color formation of natural alexandrite and synthetic alexandrite are similar.Natural alexandrite and synthetic alexandrite are different from trace elements,infrared spectral characteristics,raman spectroscopy.Natural alexandrite contains Ti,V,Cr,Fe,Ga,Zr,synthetic alexandrite contains V,Cr,Sr.There are some vibrational peaks at 3600-2300 cm-1 in natural alexandrite,such as 3387 cm-1O-H,3018 cm-1,2891 cm-1 Be-O and M-O,2483 cm-1,2360 cm-1C-O vibrational peaks,but synthetic alexandrite don't have.Raman spectroscopy has a difference in FWHM,the FWHM of natural alexandrite are greater than 17.0 cm-1,and the FWHM of czochralski synthetic alexandrite are less than 17.0 cm-1.Chemical composition,crystal structures and the mechanism of color formation of natural crystal and synthetic crystal are similar.Infrared spectral characteristics and the FWHM of raman spectroscopy are different,natural colorless crystals are characterized by 4547 cm-1 O-H band,synthetic green crystal only contains 5200 cm-10-H absorption peak,natural amethyst have O-H vibrational band at 3500-3000 cm-1,while synthetic amethyst only have three sharp O-H absorption peaks,synthetic citrine only contains 5180 cm-1 O-H absorption peak.The FWHM of natural crystal are greater than 6.5 cm-1,and the FWHM of hydrothermal synthetic crystal are less than 6.5 cm-1.Major chemical composition and crystal structures of natural spinel and synthetic spinel are similar.Natural spinel and synthetic spinel are different from trace elements,coloring mechanism,infrared spectral characteristics and the FWHM of raman spectroscopy.Natural spinel contains V,Cr,Fe,Zn,Ca,synthetic spinel contains V,Cr,Fe,Ti,Co.The coloring elements of natural blue and purple spinel are Fe.The coloring elements of synthetic blue spinel are Cr,Fe,Co.The coloring elements of synthetic green spinel are Fe,Co.Synthetic spinel have two O-H band at 3528 cm-1 and 3353 cm-1,natural spinel don't have absorption peak at 6000-3000 cm-1.Raman spectroscopy has a difference in FWHM,the FWHM of natural spinel are greater than 10.0 cm-1,and the FWHM of synthetic spinel by Verneuil process are less than 10.0 cm-1.Major chemical composition and crystal structures of natural opal and synthetic opal are similar.Natural opal and synthetic opal are different from trace elements and infrared spectral characteristics,natural opal contains Si,Fe,Cu,synthetic opal only contains Si.Different coloring mechanism,the body color of natural opal are associated with Fe,Cu,the color of synthetic opal is associated with the arrangement of the spheres.Synthetic opal are characterized by O-H band at 5812 cm-1 and 5720 cm-1.The infrared spectra and Raman half width of law can provide effective help that it can identify natural alexandrite and synthetic alexandrite by Czochralski method,natural crystal and synthetic crystal by hydrothermal,natural spinel and synthetic spinel by flame fusion method.But natural opal and synthetic opal by chemical precipitation method using infrared absorption characteristics of synthetic opal identification is more effective.