Abstract:

A multiple-treatment process was developed to produce orange-pink-red coloration into both natural and synthetic diamonds through the controlled introduction of NV centers, including HPHT annealing and subsequent irradiation and annealing. Most of these processed diamonds are Type Ia, coloured by the N3 center and high concentration of the NV center, result in deep purplish red to deep red diamonds. With the development of technology, there have been type IIa multiple-treatment pink diamonds on the market in recent years, which have lower nitrogen content and more vibrant pink hue compared to Type Ia diamonds. And the color of such processed diamonds is closer to untreated natural pink Type IIa diamonds coloured by NV centres, treated synthetic diamonds coloured by the introduction of NV centres. Two multiple-treated natural pink diamonds have been tested and analysed in detail to better understand their identification characteristics and to facilitate differentiation from other types of Type IIa pink diamonds. Graphitized fractures and crystal inclusions were visible under the microscope. UV-Vis-NIR spectra collected at liquid-nitrogen temperature showed strong GR1 and NV centers, the emissions of the NV centers were superimposed on the absorption spectrum. The different concentration of the NV and GR1 defects resulted in different hues of the two diamonds, one purplish pink and the other is orangy pink. In the near-infrared region, the dominant feature was strong absorption band at 9,287 cm^-1,which has been reported to be related to irradiation treatment. Irradiation-related PL peaks 3H, GR1 and 595nm absorption were detected. The growth structure under DiamondView is still the main identification basis for natural and synthetic pink diamonds.

Key words: pink diamond, NV center, type IIa diamond, multiple treatment, irradiation and annealing