Qingchao Zhou

Sunstone is a member of the feldspar group. Natural sunstones from Oregon exhibit unique optical effects and hold significant market value. However, since 2008, there has been a persistent issue of diffused red feldspars masquerading as natural sunstones in the market, severely undermining consumer confidence in purchasing natural sunstones. Fluorescence characteristics under 305–335 nm ultraviolet excitation are considered an effective method for distinguishing copper-diffused red feldspars from natural sunstones. In this paper, through detailed analysis and testing of ten market-acquired red and green feldspar samples, including UV-vis spectra, microscopic characteristics, fluorescence spectra, and chemical compositions, we validate the efficacy of fluorescence characteristics in identifying copper-diffused feldspars. The results verify the widespread prevalence of copper diffusion treatment in market-acquired red and green feldspars, shedding light on their treatment history and providing valuable insights for jewelry consumers. This research not only enhances our understanding of sunstone treatments but also strengthens the reliability and applicability of fluorescence spectroscopy in gemstone identification, offering promising prospects for its broader adoption in the jewelry market.

The commercial application of colloidal semiconductor nanocrystals has been realized owing to the development of composite film technology. Here, we demonstrated the fabrication of green and red emissive CuInS₂ nanocrystals embedded polymer composite films of equal thickness by using a precise solution casting method. The impacts of polymer molecular weight on the dispersibility of CuInS₂ nanocrystals were then systematically studied through evaluating the decrease in transmittance and red shift of emission wavelength. The composite films made from PMMA of small molecular weights exhibited higher transmittance. Applications of these green and red emissive composite films as color converters in remote-type light-emitting devices were further demonstrated.

Owing to the high market values of natural sunstones in Oregon, a kind of artificially diffused red feldspar exhibited at the Tucson Exhibition at the beginning of this century, whose color origin is the same as that of natural sunstone (copper nanoparticles). However, the details of the artificial diffusion process are less disclosed, there is no systematic method to obtain such gemstones. In this paper, we developed the high-temperature copper diffusion process for the surface recoloring of faceted labradorites, which are partly buried in the diffusant. By optimizing the experimental parameters of high-temperature copper diffusion, we successfully recolored the faceted labradorites to red and light red. The gemological and spectroscopic characteristics of the recolored faceted labradorite were further characterized. The red and light-red faceted labradorites exhibited the unique surface plasmon resonance absorption peaks of copper nanoparticles near 580 nm, which is the origin of red color. The typical inclusions formed in the faceted labradorite is in the shape of “fire cloud”. The interface of red and light-red faceted labradorite that is in contact with the diffusant is less contaminated, we believe that the contamination could be further reduced or eliminated by optimizing the high-temperature copper diffusion process. The way that the sample is in contact with the diffusant partly is versatile and promising in the surface treatment of materials that have already been processed.