Photochemical Transformations and Nanocluster Formation on the Surface of Zircon (ZrSiO₄) Induced by CO₂ Laser Radiation

Abstract

We investigate the photochemical transformations caused by the continuous CO₂ laser radiation (10⁵−10⁶ W/cm²) as well as by the pulsed CO₂ laser irradiation with a pulse energy of 3–4 J, a pulse duration of 200 ns, and an effective diameter of the laser spot of 1 mm on the surface of zircon (ZrSiO₄). We study the X-ray emission spectra and photoluminescence of the sample surface after the CO₂ laser irradiation. We establish that the action of laser radiation in the infrared range on crystalline zircon leads to selective sublimation of Silicon (Si_mO_n) complexes and find increase in the content of Zr atoms and a decrease of Si atoms on the surface of the irradiated samples. The analysis of X-ray emission spectra of samples after CO₂ laser irradiation shows also that there is a redistribution of the intensities of the K and L components in the spectra of irradiated zircon. The processes of increase in the Zr content and decrease of the Si content at the irradiated samples and the redistribution of electrons over the K and L shells of the Zr atoms can be caused by the resonant breaking of the Si–O bonds induced by the CO₂ laser action; this leads to the creation of long-lived Zirconium–Oxygen defect nanoclusters [Zr[ · ]⁺Zr]ⁿ⁺ and [Zr[ · ]⁺Si]ⁿ⁺ on the surface of zircon induced by laser irradiation, where symbol [ · ]⁺ means an Oxygen vacancy and n is a charge of nanoclusters. Arising of such nanoclusters is confirmed by the photoluminescence spectra of laser irradiated samples. These spectra demonstrate the intense line of complicated form at a region of 400 nm. The feature of Zirconium nanoclusters shows that, in the clusters, the Zirconium atoms stay in different electronic states.