Abstract：“Edison” pearls and “Gabriel” pearls are high-quality freshwater cultured pearls that have greatly enriched the market in recent years. They are similar to South Sea pearls and AKOYA pearls respectively. Nowadays, detecting color origin and variety of these pearls has become problematic for gem testing labs. This paper obtained the photoluminescence (PL) spectra of 132 pieces of various types of pearls in natural colors and enhanced colors including white, golden, black and silver-grey series from a Raman spectrometer. After comparing and analyzing the PL spectra of different types of pearls, important PL characteristics were identified. The ratio between the fluorescence background intensity and the main aragonite peak at 565 nm (F/A) in a PL spectrum is critical for distinguishing between different types of white pearls and identifying if the black, golden, and silver-grey pearls have been color enhanced. (1) The F/A values of South Sea white pearls are typically close to 1; the PL spectra and F/A value of white Edison pearls and Gabriel Pearls are very similar, most of which showed a peak at 631 nm, with F/A values clustering at 2; and white AKOYA pearls have significantly higher F/A value(>10). (2) The F/A ratios of South Sea golden pearls cluster at 1.6, with small variations, whereas the F/A ratios of dyed South Sea golden pearls and dyed “Edison” pearls are significantly higher (>4). (3) The South sea black pearls with dark grey body colors have no characteristic luminescence peaks, but as the deepening of color, a peak at 617 nm appears and gradually heightens. The South sea black pearls with black body colors have characteristic peaks at 617 and 650 nm, related to organic porphyrins. Most of the dyed and irradiated black samples did not show obvious fluorescence background enhancement. (4) The F/A values of naturally colored silver-grey AKOYA samples are less than 3, while the F/A values of dyed and irradiated silver-gray AKOYA samples are distinctively higher ranger (1.79~144), and there is a variation in different color treatment.
Key words：Photoluminescence spectra; Pearl; South Sea cultured pearl; AKOYA pearl; Freshwater nucleated cultured pearl
陈彩云飞，李立平. 光致发光光谱在鉴别不同类型珍珠中的应用[J]. 光谱学与光谱分析, 2022, 42(01): 20-25.
CHEN Cai-yun-fei, LI Li-ping. The Application of Photoluminescence Spectra on Identification of Different Types of Pearls. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2022, 42(01): 20-25.
