光致发光光谱在尖晶石热处理检测中的应用

Application of Photoluminescence on Identification of Spinel by Heat Treatment

近年来,光致发光光谱被广泛应用在合成和处理钻石的检测中,然而由于在其他宝石上的研究尚不 系统,使得光致发光技术未得到广泛的应用,尤其在实际检测中的应用并不广泛.同时,随着尖晶石在宝石市 场上的兴起,合成和处理尖晶石的方法和检测已经成为宝石学上不得不重视的问题,因此光致发光光谱是一 种值得关注且十分有效的检测手段.在超过相变温度后,随着热处理程度的加深,尖晶石有序无序变化程度与温度成正相关关系.本文将天 然红色尖晶石样品在管式炉中进行不同温度的热处理,并通过淬火保留该温度下尖晶石的结构状态,再通过 对样品在低于相变温度下的退火实验来探究尖晶石相变还原的可能性.光谱测试上,通过在液氮环境下的测 试手段获得更加清晰的尖晶石光致发光光谱,并获得光谱参数.通过对不同处理温度下淬火尖晶石光致发光光谱参数的分析,可知相变温度约为700℃左右.随着尖晶 石相变程度的加深,光致发光光谱的谱峰宽度不断增大, R-line与 N-line的相对高度逐渐减小,这些在谱峰参 数上的明显变化可以作为尖晶石处理及合成检测中的可靠依据.值得注意的是,尖晶石的相变程度会随着退火时间的加长而部分还原.通过在700°C、650°C和 600 °C下 对尖晶石进行不同时间长度的退火实验,并分析退火时间长短与相应光谱的参数后,得出如下结论：通过退火 处理,尖晶石有序度虽然会发生一定程度的还原,但是并不会完全恢复到原本该温度下样品的有序度状态,这 提高了光致发光在尖晶石处理品、合成品与天然样品鉴别中的可信度.

Recently, the photoluminescence （ PL ） has been studied intensively and applied widely in the detection of diamonds,but not in the other gem materials. This may be attrib-uted to the rare PL research on other kind of gemstones. Meanwhile, with more and more spinels appearing on the jewelry market, we have to pay attention to the problem of the iden-tification of treated and synthetic spinels. To solving this, photoluminescence may be an effi-cient method.Above the order-disorder phase transition temperature, the degree of transition is proportion to the increasing of temperature. We heated spinel samples in tube furnace to differ-ent temperatures, and maintained the structure conditions by rapid quenching. After that, we explored the possibilities of reversing the transition by annealing the samples below the transition temperature. In order to get some sharp and clear spectrum with accurate parame-ters, the PL spectra were taken at liquid nitrogen condition.After analyzing the spectral parameters of quenched samples, the spinel transition tem-perature is about 700℃. With treatment temperature risen the FWHM of P peaks b e come bigger and the ratio of relative intensity of R-lines and N-lines become smaller. Such chan-ges can be a reliable evidence of distinguishing treated and synthetic spinels. What should be pay more attention is the degree of transition can return to a partially ordered state by long time annealing. We annealed the samples at 700℃,650℃ and 600℃ for several days,and then got their corresponding spectra. We explored the relationship between the annealing time and the parameters of PL spectra after annealing. Through this research, we discovered that the PL spectra can only be partially restored to a more ordered state, however, we were not able to completely restored to a fully ordered state. Therefore,the application of the PL spectra in identifying synthetic or heated spinel still seems to be very robust.