Sn codoping effects on the photoluminescence of SiO2:Ge

We present an observation of the photoluminescence features introduced by Sn doping in the SiO2:Ge core of an optical fiber preform, excited in the vacuum-ultraviolet energy region by synchrotron radiation. Detailed measurements as a function of the excitation energy indicate the presence of two specific emissions around 3.5 and 3.7 eV related to two excitation channels at 5.7 and 5.9 eV, underlying an absorption band centered at about 6 eV. These data put in evidence the capability of Sn to introduce specific optically active defect configurations, contrary to Ge, which mainly introduces perturbations on otherwise intrinsic oxygen-deficient-center sites.