Highlights
- Investigation of luminescence and structural properties using various methods.
- The triclinic structure was preserved after annealing as shown by Raman, XRD, FTIR.
- UV-Vis spectra differ between blue and green samples due to impurity type and concentration.
- For the first time, OSL and TL results are compared for samples of different colors.
Abstract
Kyanite (Image 1) is an aluminum silicate with a triclinic crystal structure and occurs naturally in various colors due to trace impurities. This study evaluates the structural and luminescent properties of natural and annealed, at 1100 oC for 1 hour, green and blue kyanite samples. The natural and annealed samples were characterized using X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), ultraviolet–visible (UV–Vis) absorption, photoluminescence (PL), thermogravimetric analysis (TGA), thermoluminescence (TL), and optically stimulated luminescence (OSL). X-ray fluorescence (XRF) analysis identified several impurities, including Fe, Ca, Ti, V, and Cr, with distinct concentrations in the blue and green samples. XRD, FTIR, and Raman results confirmed the preservation of the triclinic structure after annealing, with minor distortions attributed to changes in structural order. The optical absorption data revealed significant differences between blue and green samples, particularly in the iron-related charge transfer bands. Image 2 emissions observed in the PL spectra appeared more prominently in blue kyanite and showed high sensitivity to thermal treatment. The TL glow curves exhibited a profile with emission from 300 to 400 K for all the samples. The results indicate that annealing increases the OSL signal and induces a faster decay profile, suggesting that the thermal treatment contributes to the creation or activation of optically active trapping centers. The outcomes highlight the influence of trace impurity type, oxidation states, and concentration on the luminescent behavior of kyanite, supporting its potential applications in radiation dosimetry, luminescence dating, and optical sensing technologies.
