Luminescence and Raman Detection of Molecular Cl₂ and ClClO Molecules in Amorphous SiO₂ Matrix

Chlorine is a common undesirable impurity in synthetic SiO₂ glass for ultraviolet optics and optical fibers. It is usually incorporated into glass as bound Si-Cl groups or interstitial Cl₂ molecules. We report a high-sensitivity detection of Cl₂ in amorphous SiO₂ (a-SiO₂) by photoluminescence (PL) and also by Raman spectroscopy. The Cl₂ PL emission band at 1.22 eV (1016 nm) appears at T < 160 K and shows a characteristic vibronic progression with separations ≈(520-540) cm^-1 and an average lifetime of ≈5 ms at 13 K. Its excitation spectrum coincides with the shape of the 3.78 eV (328 nm) optical absorption band of Cl₂ in a-SiO₂, corresponding to the X → A ¹Π_u transition to repulsive excited state. Direct X → a singlet-to-triplet excitation was also observed at 2.33 eV (532 nm). Cl₂ PL may serve as a sensitive and selective tool for monitoring Cl impurities and their reactions in a-SiO₂. A Raman band of Cl₂ is found at 546 cm^-1. Cl₂ photodissociation at energies up to 4.66 eV (266 nm) was not detected, pointing to a strong cage effect in a-SiO₂ matrix. However, 7.9 eV (157 nm) photolysis of interstitial O₂ molecules gives rise to a Raman band at 954 cm^-1, indicating a formation of dichlorine monoxide isomer, ClClO molecule by reaction of O atoms with interstitial Cl₂. (Graph Presented).