APPLICATIONS OF PHOTOLUMINESCENCE IN SPINEL IDENTIFICATIONS

Recently, the photoluminescence (PL) has been studied intensively and applied widely in the detection of diamonds, but in the other gemology areas, have not been explored systematically.(Hainschwang et., 2013) This may be attributable to the rare research on other kinds of gemstones. Meanwhile, with more and more spinels appearing on the jewelry market, we have to pay attention to the problem of the identifying of treated and synthetic spinels. To solving this, photoluminescence may be an efficient method.

Above the phase transition temperature, the degree of order-disorder transition is proportion to the increasing of temperature. We have heated spinel samples in tube furnace to different temperatures, and maintained the structure conditions by quenching. After that, we explore the possibilities of returning to the order condition by annealing the samples below the transition temperature. In order to get some sharp and clear spectra with accurate parameters, the PL spectra were taken at liquid nitrogen condition.

The transition temperature results in about 700℃，after analyzing the PL spectra parameters of quenching experiments. The spectrum can also be applied to indicate the degree of disorder transition (corresponding to the heated temperatures), which can be a reliable evidence of distinguishing treated and synthetic spinels.

The degree of transition can return to a partially ordered state by long time annealing. 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 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.

References：

Hainschwang T., Karampelas S., Fritsch E., Notari F. (2013), Luminescence spectroscopy and microscopy applied to study gem materials: a case study of C centre containing diamonds, Mineralogy and Petrology, Vol. 107, Issue. 3, pp. 393-413.