Characterization of Burmese Amber with Three-Dimensional Fluorescence
BAI Ying1, ZHENG Xiao-hua1,2, YIN Zuo-wei1*
1. Gemological Institute, China University of Geosciences，Wuhan 430074, China
2. School of Jewelry, West Yunnan University of Applied Sciences, Tengchong 679100, China
Abstract：As a kind of organic gemstone, amber generally has a fluorescence phenomenon. In this paper, the three-dimensional fluorescence spectra were adopted to explore the spectral characteristics of Burmese amber, which served as the object of study. The results showed that for Burmese golden amber and brown amber, which emit glaringly bluish-white fluorescence under long-wave ultraviolet radiation, there was a fluorescence peak in the three-dimensional fluorescence spectra, the scope of the peak was about λex350～400 nm/λex400～450 nm, and the main fluorescence peakwas positioned at λex360 nm/λem425 nm, with high fluorescence intensity. For the Burmese blood amber, which glows in earthy yellowish fluorescence under long-wave ultraviolet, its fluorescence peaks were located at about λex420～520 nm/λem500～580 nm, and the fluorescence peaks were scattered in multiple small peaks, with weak fluorescence intensity. Heating the golden amber and brown amber samples under oxidizing conditions produced baked “blood amber”, and it was found by comparing its three-dimensional fluorescence spectra before and after baking that fluorescence peaks of the baked “blood amber”, compared with those before baking, were red-shifted, from λex480～530 nm/λem520～570 nm, with extremely weak fluorescence intensity, which was consistent with the fluorescence characteristics of the natural blood amber. The infrared absorption spectrum demonstrated that oxidation caused the concentration of oxygen-containing groups such as carbonyl C═O in the molecular structure of blood amber and baked blood amber to increase. As a strong chromophore group, Carbonyl C═O made amber in a red appearance with its increased concentration and absorption intensity. Meanwhile, as an electron with drawing substituent, Carbonyl C═O replaced the H atom in the molecular structure and linked with the impurity atom with no bonding, producing n→π*1 transition, making the fluorescence intensity of amber weakened, and even quenched, as well as facilitating the fluorescence peaks to shiftin the long wavelength direction. The Three-dimensional fluorescence spectra can present the fluorescence phenomena of Burmese amber in a fast and effective manner, and provides a new analysis tool for the study of amber’s fluorescence characteristics and molecular structure.
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