Fine structure of a core-shell system in photo-thermo-refractive glass

We report the results of a thorough investigation into the initial stages of the photo-thermo-induced crystallization process in photo-thermo-refractive glass. The spectral location of the absorption peak characteristic of the surface plasmon resonance in the silver nanoparticles is known to be highly sensitive to the dielectric parameters of the nanoparticle surrounding. We have studied the evolution of the peak location in the course of PTI crystallization process and shown that the red shift of the peak in glass is caused by the occurrence, around the silver nanoparticles, of highly-refractive shell of a mixed nature. The blue shift of the peak that can be observed under the reduced speed of the process was shown to be inflicted by the precipitation of sodium fluoride crystals. During further analysis was proven that shell is of 5.7 angstrom thickness. A couple of models examining shell possible evolution was proposed, namely sodium bromide and silver bromide crystal solid solution and silver bromide inclusions into the surrounding glass layer. Both approaches were modeled to obtain surface plasmon resonance shifts equal to experimentally observed ones. It was shown also that the observed blue shift of the plasmon resonance peak at the later stage of PTI crystallization is due to the NaF precipitation.