Magnetic Resonance and Optical Study of Carbonized Silica Obtained by Pyrolysis of Surface Compounds

Abstract

The carbonized silica (SiO2:C) nanopowders were prepared by chemical modification of fumed silica (aerosil) by phenyltrimethoxysilane followed by thermal annealing at temperature in range of 500-800 °C in nitrogen flow. Their magnetic properties were investigated by electron paramagnetic resonance (EPR) in the temperature range from 4.2 K to 292 K. The initial and annealed SiO2:C samples revealed carbon (C) related defects. The carbon related radicals (CRR) in annealed SiO2:C nanopowders withg-factors 2.0042, 2.0039 were attributed to the oxygen (O)-centered CRR and C-centered CRR with a nearby O heteroatom, respectively. The EPR data were compared with infrared (IR) and photoluminescence (PL) data. It was found that the position of the PL band depends on the type of CRR formed after sample annealing. The PL with maximum intensity at 440 nm was found for the sample annealed at 500°C in which O-centered CRR was observed while in the sample annealed at 600°C in which C-centered CRR with a nearby O heteroatom was observed and graphite-like amorphous C clusters were appeared the peak of the PL band was shifted to the 510-520 nm.