Bleaching of optical activity induced by UV Laser exposure in natural silica

TL;DR

This study investigates how UV laser exposure causes bleaching of optical activity in natural silica, focusing on the transformation of Ge-related centers and the effects of OH content.

Contribution

It provides experimental data on UV-induced transformations in natural silica with different OH contents, highlighting the conversion of Ge centers into H(II) centers.

Findings

UV irradiation reduces specific absorption and emission bands in silica.

Bleaching is mainly due to conversion of Ge'' centers into H(II) centers.

Silica with low Ge concentration shows unique UV-induced transformation behaviors.

Abstract

We report experimental data on two types of natural silica, differing for their OH content, irradiated with UV photons (4.66 eV) from a pulsed Nd:YAG laser. Irradiation induces a reduction of the absorption band at 5.12eV and of the associated emissions at 3.14eV and 4.28eV, ascribed to twofold coordinated Ge (=Ge'') centers pre-existing in our samples. The bleaching is mainly due to the post-irradiation conversion of =Ge'' into the paramagnetic H(II) center via trapping of a H atom. Comparison with literature data points out the peculiarities of silica with a low Ge concentration as regards UV induced transformations.