Spectral Characteristic of 405 nm Photoluminescence in Abnormally Fluorescent Colourless Melee Diamond

In the screening of melee diamonds, the mixing of synthetic and natural diamonds remains a persistent issue. For colourless melee diamond samples, the NGTC Shenzhen Laboratory conducted a preliminary screening based on fluorescence and phosphorescence characteristics under short-wave ultraviolet. For samples exhibiting non-blue fluorescence, photoluminescence (PL) spectroscopy under 405 nm laser excitation was further performed. The results indicate that, in addition to the commonly observed blue fluorescence, natural melee diamonds may also display yellow, red, green, or deep blue fluorescence, and phosphorescence can be observed in a few natural samples. Their PL spectra commonly exhibit emission peaks at 415, 496, 503 nm, and 741 nm. Some samples also show emission peaks at 737 nm associated with SiV^- defects, peaks related to nickel defects, and a fluorescence band around 560 nm. CVD-grown synthetic melee diamonds typically exhibit red fluorescence, with some showing green, yellow, or orange fluorescence. Their PL spectra are characterized by emission peaks at 468 nm and 737 nm, along with their respective phonon sidebands. HPHT-grown synthetic melee diamonds often exhibit green-blue fluorescence and phosphorescence, with PL spectra showing characteristic emission peaks at 883 nm and 884 nm associated with nickel-related defects.