The effect of heat treatment on zircon color and its enhancement mechanism.

ABSTRACT

The effect of heat treatment on zircon color was studied from a new perspective of chromaticity of gemstones. The mechanism behind zircon color enhancement was investigated through the combination of infrared spectroscopy, X-ray diffraction, Raman spectroscopy, and UV-vis spectroscopy. The study reveals that the color of zircon has no significant correlation to the degree of metamorphism, which decreases as heating temperature rises. Type I and Type II defects in zircon are characterized by the deletion of an oxygen atom at the nearest site to Y3+ occupied by the Zr4+ and the loss of electrons at the next nearest oxygen atom to Y3+, respectively. These defects lead to broad absorption bands in the UV-vis spectra ranging from 340 nm and 500 nm, respectively. Additionally, there is a correlation between the color of zircon and the strength of the relationship between the two absorption bands. After undergoing heat treatment, the first defects to be repaired were type II, followed by type I. Subsequently, the zircon appeared colorless after both types of defects had been corrected.