Spectroscopic characterization of diamonds colored by the 480 nm absorption band

Diamonds colored by the 480 nm absorption band - known as "480 nm band diamonds" - are relatively rare among natural untreated colored diamonds. This group includes some of the most highly valued colored diamonds with unmodified orange hues, as well as chameleon diamonds, which have a reversible color-change property when exposed to heat or left in the dark for a period of time. Due to their rarity, most of the optical properties of 480 nm band diamonds have not been fully characterized, and little is known about the mantle environments in which these diamonds formed. In this study, we document the gemological and spectroscopic features of one rough and 100 faceted 480 nm band diamonds, of which 40 faceted diamonds have chameleon properties. We report surface fluorescence patterns, UV-Vis-NIR absorption spectra, FTIR spectra and PL mapping results of all 480 nm band diamonds in this study, as well as their mineral inclusions identified using Raman spectroscopy. We find that chameleon diamonds tend to have a weaker 480 nm absorption band compared to non-chameleon diamonds with 480 nm absorption band. Chameleon diamonds generally have higher nitrogen concentrations (mean = 100 ppma) than non-chameleon diamonds (mean = 30 ppma). The absorption peak at 1344 cm(-1) corresponding to single substitutional nitrogen is detected in some 480 nm band diamonds. Hydrogen impurities are present in all diamonds and a total of similar to 50 absorption peaks corresponding to hydrogen-related defects are detectable in these diamonds. When exposed to deep UV (< 230 nm), most 480 nm band diamonds have irregular surface fluorescence patterns with strong zonation of distinct fluorescence colors, primarily yellow and blue. Approximately 200 distinct PL peaks are detectable in the yellow fluorescence zones of the diamonds in this sample set, with peaks related to nickel impurities detectable in all diamonds. Conversely, those areas of the diamond with blue surface fluorescence generally have relatively featureless PL spectra, with only N3 centers detectable in many diamonds. Mineral inclusions are observed in 15 diamonds in our study, all of which have an eclogitic paragenesis. These mineral inclusions indicate that the inclusion-bearing 480 nm band diamonds formed in the subcontinental lithospheric mantle, where eclogite is one of the major diamond host rocks.