Multispectral Analysis of Natural Tridymite: Morphology, Composition, and Luminescence Features

In this study, tridymite mineral from Lanzarote, Canary Islands, was investigated using spectroscopic and luminescence techniques for potential applications in dosimetry (e.g., radiation detectors), dating (e.g., through luminescence techniques), and ceramics (as a high-temperature-resistant material). Raman scattering identified molecular vibrations at 155, 220, 320, 370, 410, 445, 800, and 1100 cm−1. The 29Si MAS NMR spectra exhibited a broad signal (75–150 ppm) indicating variations in the silicon environment, supported by environmental scanning electron microscopy-energy dispersive X-ray spectroscopy (ESEM-EDS). Electron paramagnetic resonance (EPR) revealed an unpaired electron in a silicon sp3 orbital (g = 2.0027), increasing with power, suggesting an oxygen vacancy. The blue cathodoluminescence (CL) band suggested oxygen-defect centers (ODCs), with emissions at 400 and 445 nm could be linked to self-trapped excitons (STE) from an oxygen Frenkel pair (Si–O–O–Si) and oxygen vacancies. Emission at 480 nm could be attributed to impurity defects such as GeO₄3− + e and AlO₄4− + e. CL data analysis provided insight into how these defects influence radiative recombination, affecting photoluminescence (PL) emissions at 693 and 694.5 nm. ODCs notably contributed to PL emissions, as evidenced by the 452.5-nm CL peak associated with oxygen vacancies. This study offers valuable insights into tridymite's crystal structure, elemental configuration, molecular dynamics, and luminescent properties.