Comparison Of Color Modification Experiment And Characteristics Of HPHT Synthetic Yellow Diamonds

In this thesis,27 samples of yellow diamond synthesized by HPHT were selected.After grouping,different irradiation doses were used for electron irradiation,followed by heat treatment to explore the effects of irradiation dose,heat treatment temperature and holding time on diamond color change.After the color change,the experimental samples changed from yellow green to red brown,and successfully realized the color change.The conventional gemmological test,microscope magnification observation,orthogonal polarizer observation,infrared spectrum,optical fiber spectrometer,photoluminescence spectrum,Raman spectrum,DiamondView^TM,three-dimensional fluorescence spectrum were studied and analyzed.Through the observation of Gemmological microscope,after the color change,the surface of the sample appears the gray black color left by high temperature treatment,and the edges of the metal inclusions inside become blurred.The polarizing condition of the samples before and after the color change was observed with the orthogonality polarizing mirror in the gemmology microscope.It was found that the abnormal extinction occurred before the color change of the samples,which still existed after irradiation and slightly weakened after heat treatment.The Raman spectrum shows that the half peak width of the sample before and after the color change is very large,which proves that the existence of the crystal internal stress and the internal stress in different growth areas are also different,leading to the abnormal extinction of the sample before and after the color change.The infrared spectrum before and after the color change shows that the diamond is always type Ib,and the existing form of nitrogen atom has not changed.The calculation method of nitrogen content in each type of diamond crystal is summarized.The nitrogen content of diamond in this thesis is about 100 ppm.The visible spectrum before and after irradiation reveals the mechanism of color change.The photoluminescence spectrum indicates that the irradiation brings a lot of defects to the diamond.After irradiation,there are 637nm peak related to?N-V?^-color center,575nm peak related to?N-V?⁰ color center,741nm peak related to vacancy,659nm peak related to Ni impurity defect,626nm peak related to nitrogen gap atom.In addition,other complex defects are introduced to varying degrees.In fact,there is 637nm peak in the synthesis of type Ib diamond by untreated HPHT.DiamondView^TM fluorescence image and three-dimensional fluorescence spectrum show that irradiation has little effect on the fluorescence of HPHT synthesized type Ib diamond.After heat treatment,the fluorescence of the sample will change obviously.Under DiamondView^TM,the fluorescence will change from yellow green to orange red,and the"cross"fluorescence will also weaken.There are four main fluorescence peaks in the three-dimensional fluorescence spectrum before and after irradiation.After heat treatment,the four main fluorescence peaks will disappear and a new strong fluorescence peak will appear.The change of fluorescence before and after sample processing can be confirmed by diamondviewtm fluorescence image and three-dimensional fluorescence spectrum.