Interaction of Surface Trap States and Defect Pair of Photo luminescent Silica Nanostructures with H2O2 and Solvents

The photoluminescence (PL) of silica nanostructures has been found to be affected remarkably by organic solvents and hydrogen peroxide. The absorption and PL emission as well as excitation spectra show a variation in the position of the spectral maxima, with the change in the solvent polarity. The most interesting effect of solvents is observed in the PL decays. The decays, which are biexponential in polar media, are single exponential in nonpolar solvents. This observation indicates the absence or destabilization of surface related trap states in nonpolar media. On the other hand, these states seem to be stabilized in polar solvents, as the long component of the PL decay is further enhanced in the dispersions in polar solvents. Such enhancement occurs, most likely, because of hydrogen bonding between the silanol groups and the solvent molecules. PL quenching is observed upon addition of H2O2. Surprisingly, this is accompanied by an enhancement in the long component of the decay. This pair of apparently contradictory observations indicates the stabilization of surface trap states with H2O2, and at the same time, formation of new, nonluminescent defect centers by a reaction between the photoluminescent defect pair and H2O2.