Spectral Characteristic of Natural and HPHT-Grown Type Ⅰb Diamonds

Natural pure type Ⅰb diamonds are rare to see, meanwhile synthetic yellow diamonds are mostly type Ⅰb. How to separate natural and synthetic type Ⅰb diamonds remains a challenge in the identification of small sized yellow diamonds. To solve the problem, infrared and Raman photoluminescence spectra as well as ultraviolet fluorescence images observations were performed on both natural pure type Ⅰb yellow diamonds and synthetic yellow diamonds which were produced in different companies domestically. The collected data were compared and analyzed. Infrared spectral analysis indicates that the nitrogen content that are low in natural diamonds are normally higher in synthetic ones, while the 1 358, 4 065, 4 110, 4 165 cm^-1 absorptions that are commonly seen in natural diamonds are often missing from the latter. According to the photoluminescence spectral analysis, synthetic yellow diamonds show nickel related defects peak at 484, 489, 494, 496.5, 883/884 nm, however natural diamonds are featured with 415.2 nm and 829/830 nm defects. Ultra-violet luminescence image stays one of the most important methods to distinguish natural and synthetic yellow diamonds, yet it can be unavailable when the diamond is too small to be observed for growth patterns clearly, and that's the case where infrared and PL spectra are required to draw the possible conclusion.