Study on the Spectral Characteristics and the Alexandrite Effect of Diaspore
ZHOU Dan-yi1, 2, LU Tai-jin2*, KE Jie2, CHEN Hua2, SHI Guang-hai1, LI Ke1
1. School of Gemology, China University of Geosciences (Beijing), Beijing 100083, China
2. National Gem & Jewelry Technology Administrative Centre, Ministry of Land and Resources, Beijing 100013, China
Abstract：Diaspore is one of industrial minerals used for extracting aluminum and making fireproofing materials. In recent years, diaspore has been found as a gemstone with alexandrite effect. However, little research has been performed on its spectral characteristics and cause of alexandrite effect. In this study, three diaspore samples with alexandrite effect were investigated with XRF, FTIR, Raman spectrometer, UV-Vis-NIR spectrometer together with measuring CIE colored parameters, and these testing results were compared with those of ordinary diaspore without alexandrite effect. It was found that all of the samples with alexandrite effect displayed yellowish green color in sunlight and brownish red color in incandescent light. Their infrared spectra and Raman spectra are the same as those of ordinary diaspore: the infrared absorption bands are concentrated at 400~1 200，1 800~2 110 and 2 900~3 000 cm-1, and the Raman characteristic peaks are mainly at 154, 331, 448, 665 and 1 189 cm-1. Compared the UV-Vis-NIR spectra with the results of chemical analysis, it is suggested that the d—d electron transition of Fe3+ and Cr3+ in diaspore made approximate transmittance between green-yellowish green (500~560 nm) and orange-red regions (600~780 nm) in visible light. Therefore, the difference in the relative spectral power distribution of ambient light source sheds great influence on the color of such diaspore. This research is the first to obtain color parameters of diaspore in simulated daylight and incandescent light. The alexandrite effect of diaspore can be quantitatively described by the change of a* and h0 color parameters obtained in different light sources. These results will not only provide scientific evidence and data support for the application extension and performance improvement of diaspore, but also serve to inspire deeper research on the optical properties of hydroxides.
周丹怡，陆太进，柯 捷，陈 华，施光海，李 克. 变色硬水铝石的光谱学特征及其变色机理[J]. 光谱学与光谱分析, 2017, 37(11): 3504-3509.
ZHOU Dan-yi, LU Tai-jin, KE Jie, CHEN Hua, SHI Guang-hai, LI Ke. Study on the Spectral Characteristics and the Alexandrite Effect of Diaspore. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2017, 37(11): 3504-3509.
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