To avoid the partial hydrolysis while mixing H2O/HNO3 mixture with TEOS/EtOH mixture, the latter was placed in an ice bath and then H2O/HNO3 mixture was added drop wise under continuous stirring [16]. The different molar compositions investigated in this work as well as the sample notations are listed in Table 1. For the cobalt-doping within the hybrid silica matrix, a solution of cobalt nitrate in eth- anol was prepared. Ethanol was chosen as the solvent for the salt solution because it was the same solvent used in the sols prepara- tion. Moreover, the nitrate salt was used because it is compatible with the silica sol which was catalyzed by nitric acid [28].