In recent years,highly saturated yellow Akoya pearls fill the market demand for golden pearls that less than 8 mm,and the sales volume increases rapidly.However,little researches have been done on the gemmological and spectroscopic characteristics of such pearls.In this paper,the gemmological characteristics,UV-Vis spectrum and photolumines-cence spectrum of 75 pieces of Akoya pearls of light-yellow to golden colour were obtained.The result shows(1)The natural coloured yellow Akoya pearls has a delicate surface texture and almost no fluorescence under long-wave ultraviolet excitation.Some colour-treated sam-ples show obvious iridescence circle at surface blemish.The uneven fluorescence in yellow or strong bluish white indicates the reagents penetrated.(2)UV-Vis spectrum shows that nat-ural yellow Akoya pearls may exhibit 360-420 nm absorption broad band and 430-470 nm narrow band,and some natural pearl samples with yellow to orange colour show narrow ab-sorption band at 405 nm generated by pigment that have similar structure to uroporphyrin.Colour-treated samples show broader absorption band at violet-blue range,and the strong absorption band below 400 nm may be caused by optical brighten agents.(3)PL spectrum shows that the ratio between fluorescence background intensity and the main aragonite peak(F/A)of naturally coloured samples clustered around 1.Most of the colour treated samples have F/A value above 10.Optical brightening agent treated pearl showed fluorescence maxi-mum at 575 nm and 610 nm.The dyed pearl might show fluorescence information between 630-650 nm.The optical brighteners and dyestuffs might bond and increase the plane rigid-ity of luminophore,and the intensity of 575 nm might significantly increase to annihilate the dyestuff fluorescence information between 630-650 nm.
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