Identification of Heat-Treated Sapphires from Sri Lanka: Evidence from Three-Dimensional Fluorescence Spectroscopy

• Published in: Crystals (Basel) Vol. 12; no. 2; p. 293
• Main Authors: Zhang, Yuyang, Chen, Meihua
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.02.2022
• Subjects: Analytical chemistry; Color; Excitation spectra; Fluorescence; Heat; Heat treatment; High temperature; Identification methods; Light; Low temperature; Oxidation; Sapphire; Spectroscopy; spectroscopy characteristics; three-dimensional fluorescence spectroscopy; Sri Lanka; China; Germany
• ISSN: 2073-4352; 2073-4352
• DOI: 10.3390/cryst12020293

Heat treatment is an important method used to improve the value of sapphires. The identification of heat-treated sapphires is a significant and challenging subject in gemology. In this study, natural sapphire samples from Ratnapura, Sri Lanka, were heated at different temperatures from 900 °C to 1500 °C. Then, the samples were examined by FTIR and three-dimensional fluorescence spectrometry. When excited by 450 nm light, most natural samples emitted a fluorescence band between 540 nm and 560 nm. This fluorescence disappeared after low-temperature heat treatment. Therefore, the presence of fluorescence between 540 nm and 560 nm is evidence of unheated sapphires from Sri Lanka. Almost all of the samples emitted fluorescence centered at 470 nm after high-temperature treatment. Therefore, fluorescence at 470 nm indicates that the sapphires from Sri Lanka were treated at a high temperature. Three-dimensional fluorescence spectroscopy can serve as a method to identify heat-treated sapphires.