Effects induced by UV laser radiation on the blue luminescence of silica nanoparticles

The effects induced on the blue luminescence centered around 2.8 eV, characteristic of silica nanoparticles, were investigated by monitoring its intensity during and after exposure to the third and the fourth harmonic of a Nd:YAG pulsed laser. The luminescence trend is found to be dependent on the UV photon energy: 3.50 eV photons induce a partial bleaching followed by a recovery in the post-irradiation stage; 4.66 eV photons cause a total bleaching permanent after the irradiation. These results are interpreted as the conversion of luminescent defects towards stable and metastable configurations.