变色硬水铝石的光谱学特征及其变色机理

硬水铝石(α-AlOOH)是铝土矿的主要组成矿物之一,常用于工业提炼铝以及制作耐火材料。近年来,一种具有变色效应的硬水铝石晶体开始在市场中出现。采用X射线荧光能谱仪、红外光谱仪、拉曼光谱仪、紫外可见近红外分光光度计以及测量颜色参数等方法获得了变色硬水铝石和无变色效应硬水铝石的光谱学特征,并探讨了其变色效应的成因。变色硬水铝石在日光下常呈黄绿色而在白炽灯下呈褐红色,其红外光谱与拉曼光谱与普通硬水铝石的特征峰较为一致,其中红外光谱中的特征峰主要集中在400~1 200,1 800~2 110和2 900~3 000cm~(-1)三个范围内,拉曼特征峰则主要位于154,331,448,665和1 189cm-1附近。对比化学成分分析和紫外可见吸收光谱的测试结果,认为Fe~(3+)和Cr~(3+)的d—d电子跃迁导致变色硬水铝石在可见光绿-黄绿色光区(500~560nm)和橙黄-红色光区(600~780nm)的透射程度较为接近,环境光源中红光和绿光相对功率分布的差异使硬水铝石产生变色效应。对变色硬水铝石在模拟日光和白炽灯光条件下的颜色参数进行了测定,结果显示不同光源下样品颜色参数a*和h0的变化,可定量地描述变色硬水铝石的变色效应。为硬水铝石的应用拓展、性能改善以及氢氧化物材料光学性质的深入探讨提供了科学依据和数据支持。

Study on the Spectral Characteristics and the Alexandrite Effect of Diaspore

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 char-acteristics 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 tes-ting 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 ～ 1200, 1800～2110 and 2900～3000 cm-1 ,and the Raman characteristic peaks are mainly at 154,331,448,665 and 1189 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 day-light and incandescent light.The alexandrite effect of diaspore can be quantitatively described by the change of a ? and h 0 color parameters obtained in different light sources.These results will not only provide scientific evidence and data support for the ap-plication extension and performance improvement of diaspore,but also serve to inspire deeper research on the optical properties of hydroxides.