LI Ying-ying1, ZHANG Zhi-qing1*, WU Xiao-hong2, Andy Hsitien Shen1*
1. Gemmological Institute, China University of Geosciences (Wuhan), Wuhan 430074, China
2. Technical Center for Industrial Product and Raw Material Inspection and Testing Shanghai Customs, Shanghai 200135, China
Abstract：Generally, fossil resins emit distinct fluorescence under ultraviolet illumination. However, their phosphorescence remains to be characterized. In this paper, six Indonesian fossil resins similar to the Dominican blue amber, are further divided into three parts：white inclusions (Part Ⅰ), dark inclusions (Part Ⅱ), and basal body (Part Ⅲ). By the infrared spectrometer, three vibration peaks at 1 384, 1 377, and 1 367 cm-1 indicate that these Indonesian fossil resins were derived from the Dipterocarpaceae plant. Firstly, we investigated three-dimensional fluorescence contours from three parts in Indonesian fossil resins. The results show the emission wavelengths covering the 330~380 nm ultraviolet area (excited by 235 nm), the 388 nm (excited by 330 nm), and the 446, 474 and 508 nm in the blue-green area (all excited by 440, 415 and 395 nm). It suggested at least two fluorophores contributing to the visible-range fluorescence. The relative concentration of these two fluorophores varies from Part Ⅰ to Part Ⅲ. Additionally, Indonesian fossil resin (copal) radiated a bright greenish-yellow phosphorescence when irradiated with a 365 nm ultraviolet light. Part Ⅱ & Ⅲ have a strong phosphorescence covering 460~650 nm with an emission center at 537 nm, while Part Ⅰ is close to 430 nm. The lifetime of 537 nm emission lasts more than 100 ms, while that of 430 nm emission is about 50 ms. These luminescence differences indicate that Part Ⅱ & Ⅲ underwent more aromatization than Part Ⅰ in the fossilization process.
