Surface excitation using deep ultra-violet (DUV) laser light has been applied to diamond which reveals growth structures, as well as photoluminescence originating from crystallographic defects features. This valuable information can aid in distinguishing natural diamonds from their lab-grown counterparts and non-diamond gemstone materials. In this research, we presented a dual photoluminescence imaging and spectroscopy setup using a 193nm argon fluoride (ArF) excimer laser, chosen for its above diamond bandgap (5.5eV) photon energy and high average power. This setup enables the detection of diamond’s characteristic photoluminescence emission features and growth patterns under room temperature conditions. Various types of diamonds, including chemical vapor deposition (CVD) as-grown, CVD grownhigh pressure high temperature (HPHT) treated, HPHT-grown, natural diamond and diamond simulant samples were characterized under this setup.
Photochromic gemstones exhibit optically controllable coloration at ambient temperatures, strongly affecting their visual appearance and potential market value. As a result, a comprehensive study of characteristic photochromic properties is required to estimate the potential influence on gemstone evaluation. A UV-Visible absorption spectrometer integrating a tunable light source for external excitation has been developed to investigate the wavelength- and time-dependence of photochromism for colored gemstones, focusing on natural, laboratory-grown, and color-treated pink diamonds. The results can be used to develop a color stabilization protocol to improve the reliability of color grading for valuable gemstones.
Gemstone identification and evaluation for jewelry pieces are limited by the interference from the surrounding metal mount and adjacent gemstones. To maintain transparency in the jewelry market, here we propose an imaging-assisted scanning Raman/photoluminescence(PL) spectroscopy for mounted gemstone measurement. The system can automatically align and measure multiple gemstones samples on a jewelry piece sequentially. The experimental prototype demonstrates capability of noninvasively measurement for separating natural diamond from its lab-grown counterparts and diamond simulants, identifying popular color gemstones, and using the color image for gemstone color evaluation and weight estimation.
Clarity enhancement is a common treatment method to improve the appearance of gemstones. Classifying the level of enhancement is an important task to gemological laboratories since it is associate with gemstone’s value. Current visual observation based evaluation requires considerable time and experience to identify the filling materials consistently. It is also unable to record the distribution, nor to quantify the visual influence of fracture filling. To improve the quality of identification, we demonstrate a treatment detection technique based on multi-excitation fluorescence imaging. The system is designed to reveal the filling materials while mitigate the background fluorescence from the mineral. Proper excitation wavelengths were selected based on preliminary spectroscopy and imaging studies. The experimental prototype used multiple light emitting diodes as the light sources; and adapted color camera combined with filters to monitor the fluorescence image of treated gemstones. This research utilized emerald treatment detection for demonstration. The system can reveal popular fillers in emerald such as oil, resin, and mixture of chemical compounds, and demonstrates rapid detection of clarity enhancement in emeralds.
Artificial color treatment techniques have been applied to pearls of less appealing colors to improve their appearances and to increase their commercial values. In addition, separation of various types of pearls could be challenging due to similar characteristics among several closely related mollusk species. Currently gemological laboratories use various spectroscopic and imaging techniques in tandem, including x-ray imaging, microscopic observation, ultra-violet to visible reflectance spectroscopy, and Raman spectroscopy for various identification purposes. Due to the complexity of the protocol, there is a strong demand for a fast and simple identification method designed for gemological laboratories or users without advanced equipment or expertise, such as pearl dealers and jewelry manufacturers. We demonstrate a fluorescence detection system for pearl’s color treatment identification and species classification. A photoluminescence excitation spectroscopy was used to select the proper excitation wavelengths. Multiple light emitting diodes were selected as the sources; and spectrometers were used to monitor ultra-violet to visible fluorescence. The system can noninvasively analyze both loose pearls and mounted pearl jewelries under normal office lighting condition. Spectral analysis protocols were used to localize the trace of treatments and classify fluorescence features between different pearl types. The primary purpose of this device is to detect commonly used color treatments. Additionally, it may also classify pearls between the most common types in seconds, as suggested by preliminary study.
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