Effects of heat treatment on red gemstone spinel: single-crystal X-ray, Raman, and photoluminescence study

Abstract

688 nm), and N3 (689 nm). N lines are caused by different Mg, Al environments of Cr 3+ . With increasing inversion parameter (x), the R line decreases in intensity and the N lines become prominent leading to strongly broadened peaks with a maximum shifted toward higher wave lengths (687.5 nm at 1,100 °C). Criteria for the detection of heat treatment on gemstone spinel applicable to gemological routine examination are provided. Extrapolation of u, a, and bond lengths from heat-treated Burma spinel toward the natural crystal suggests a retrograde "closing temperature" of ca. 400 ± 100 °C at which Mg, Al disorder was frozen.

Effects of Heat Treatment on Spinels as Determined by Vis/Nir and Raman Spectroscopy and XRD

“…Their peaks have stretched or increased along the x-axis. The widening of the peaks points to evidence of the bond strengths within the crystal structure mentioned in research by Widmer et al, 2014. The spectra changes are noticeable in Figure 11 but it should be confirmed in another way. To prove that the spectra are different, a PCA analysis was made to compare the same colored spinels from each experiment.…”

“…Samples are typically analyzed before and after heating, so the results can be compared. Widmer et al (2014) share their experimental results in their research on spinel spectra. Their spinels were exposed to 600, 700, 800, 850, 1000, and 1100°C.…”

“…If cobalt is bonded in the bsite, or octahedral site, the spinel may be pink (D'Ippolito, 2018). along the x-axis which shows that the bond strength has changed in some way (Widmer et al, 2014).…”

“…The spectra show a normal spinel signature for the non-heated sample, but with each increase in temperature, the peaks in the spectra widen. The peaks widths are measured and show that the bond strengths have changed in these samples after being exposed to temperatures starting at 600°C (Widmer et al, 2014). These spectra examples are shown in Figure 2.…”

“…Lee's results show that certain heats change their bonding strengths at a molecular level (Lee et al, 2009). Though heat by itself will not change the spinel samples compositionally, the tetrahedral sites, octahedral sites, and their bond strengths can change (Widmer et al, 2014). This research on spinels includes gathering Raman Spectroscopy before and after heat treatment to determine whether heat can change the bonds of samples.…”