Spectroscopic Characteristic of Orange Red to Purple Colour-Treated Diamond from Lotus Colors, Inc.U.S.A.

Colour diamonds are becoming more and more popular in China. Along with the advance of diamond colour treatment studies, diamonds can now be treated by means of multiple processes and achieve a variety of colours in appearance. In this paper, we study the characteristics of gemmological characteristics and spectral characteristics of 39 purple and orange colour-treated diamonds produced by Lotus Colors, Inc. USA., Through long-wave and short-wave ultraviolet fluorescence, micro-infrared spectroscopy, micro-ultraviolet visible spectroscopy, and photoluminescence spectroscopy.The analysis shows that the fluorescence reaction of this batch of samples is different from that of natural diamonds. The long-wave ultraviolet fluorescence has a white-coloured appearance and presents multiple colour combinations.After micro-infrared spectroscopy, it is divided into Ia type and IIa type, and has H1a, H1b, H1c characteristic peaks after irradiation and annealing.The micro-ultraviolet visible spectroscopy and photoluminescence spectroscopy can be seen in the visible N-V center.Some samples can detect weak H3, H4 center and GR1 center in the micro-ultraviolet visible spectroscopy.We guess that these diamonds may have gone through multiple processing technology. The combination of the N3 center with the (N-V)⁰, (N-V)^- resulted in a very saturated violet-orange colour appearance.