光致发光光谱在鉴别不同类型珍珠中的应用

爱迪生珍珠和珈百丽珍珠为近年来相继问世的优质淡水有核珍珠，分别酷似南洋珠和AKOYA珍珠，如何区分白色珍珠、金色珍珠、黑色珍珠及银灰色珍珠的类型和颜色成因，成为目前检测机构棘手的难题。对132颗不同类型的白色系、黄色系、黑色系、灰色系天然呈色珍珠与染色或辐照改色的各类珍珠进行了系统的PL光谱测试分析，结果表明不同类型的珍珠PL光谱有重要鉴别特征，尤其是PL光谱中荧光背景强度(F)与565 nm文石主峰强度(A)比值F/A，可有效区分不同类型白色珍珠以及黑色、金色银灰色珍珠的颜色成因。（1）白色南洋珠F/A值多集中于1附近，白色爱迪生珍珠与白色珈百丽珍珠具有类似的PL光谱与F/A值变化范围，但大部分样品出现631 nm发光峰，F/A值多集中于2；白色AKOYA珍珠的F/A值大于10。（2）金色南洋珠的F/A值多集中于1.6，变化范围较小，染金色南洋珠与染金色爱迪生珍珠F/A值基本都大于4。（3）深灰色体色Tahiti黑珍珠没有特征的发光峰，但随着颜色加深，逐渐出现617 nm处发光峰，黑色体色Tahiti黑珍珠具有稳定的有机卟啉相关的617和650 nm处发光峰；而绝大部分染色、辐照的黑色珍珠样品并未出现明显的荧光背景增强现象，但缺失617和650 nm处发光峰。（4）天然呈色银灰色AKOYA样品F/A值都小于3，而染色和辐照成因的银灰色AKOYA的F/A值都明显高（1.79~144），并且因改色方式不同，存在一定的变化范围。

The Application of Photoluminescence Spectra on Identification of Different Types of Pearls

“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.