Title
The Covariation of Color and Orange Fluorescence Instabilities in Yellow Sapphires
Author
Yang, Yunqi (China University of Geosciences, Wuhan; Hubei Gems and Jewelry Engineering Technology Research Center)
Wang, C. (TU Delft Applied Geology; China University of Geosciences, Wuhan; Hubei Gems and Jewelry Engineering Technology Research Center)
Wang, Chengsi (China University of Geosciences, Wuhan; Hubei Gems and Jewelry Engineering Technology Research Center)
Shen, Xibing (China University of Geosciences, Wuhan; Beibu Gulf University)
Yin, Ke (China University of Geosciences, Wuhan)
Chen, Tao (China University of Geosciences, Wuhan; Hubei Gems and Jewelry Engineering Technology Research Center)
Shen, Andy Hsitien (China University of Geosciences, Wuhan; Hubei Gems and Jewelry Engineering Technology Research Center)
Algeo, Thomas J. (China University of Geosciences, Wuhan; University of Cincinnati)
Hong, Hanlie (China University of Geosciences, Wuhan)
Date
2023
Abstract
In recent years, some sapphires were found to fade in sunlight and to increase their color after UV irradiation. This unstable color phenomenon is attributed to the photochromism of corundum. The photochromic effect seriously affects the grading and evaluation of sapphires, although its mechanism is still uncertain. Here, we performed a set of photochromic experiments on sapphire specimens using a 254 nm shortwave UV light source and a D65 light source (which simulates sunlight) to generate different color states exhibiting characteristic absorption, emission, and excitation spectra. We observed that, for different color states, variation in the intensity of the absorption band at ~460 nm was consistent with that of orange fluorescence at 500–800 nm. This observation indicates a relationship between color instability and orange fluorescence. Peaks in excitation spectra at 320, 420, 490, 560, and 637 nm provide insight into the source(s) of excited orange fluorescence, which are related to different types of F-centers and Mg-trapped holes. We propose an explanation for the photochromic phenomenon: the color of photochromic yellow sapphire is the result of a variety of defects that release orange fluorescence simultaneously. Further, we hypothesize that the mechanism of photochromism in yellow sapphires is linked to electron transfer between F-centers and Mg-trapped holes.
Subject
corundum
defect
excitation spectrum
F-center
photochromic
trapped hole
To reference this document use:
http://resolver.tudelft.nl/uuid:907a6b1a-062c-429b-abb7-c8a83dc5562d
DOI
https://doi.org/10.3390/min13050663
ISSN
2075-163X
Source
Minerals - Open Access Mining & Mineral Processing Journal, 13 (5)
Part of collection
Institutional Repository
Document type
journal article
Rights
© 2023 Yunqi Yang, C. Wang, Chengsi Wang, Xibing Shen, Ke Yin, Tao Chen, Andy Hsitien Shen, Thomas J. Algeo, Hanlie Hong