Photoluminescence of Di-Ureasil Hybrids Doped with Silica Coated Ag Nanoparticles

Photoluminescence of di-ureasil hybrids containing homogeneously dispersed Ag nanoparticles, covered with silica shells was investigated at room temperature and compared with emission of undoped hybrids. Metal-doped di-ureasils show a broad emission band in the blue spectral region similar to what has been observed in pure di-ureasils but with lower relative intensity. A broad minimum arises around 438 nm for Ag@SiO2 - containing di-ureasils which coincides with the peak of plasmon resonance band in the absorption spectrum. This behaviour can be attributed to inner filtering effect, which manifests itself as absorption by metal nanoparticles of light emitted from the matrix. Low-temperature time-resolved spectroscopy and lifetime measurements demonstrate that changes are induced in the time-scale behind the di-ureasil host emission when the nanoparticles are incorporated. In particular, the lifetime values for Ag@SiO2- doped di-ureasils are smaller than those measured for the undoped host, suggesting that energy transfer might exist between the hybrid's emitting centres (NH groups and siliceous nanodomains) and the nanoparticles.