Effects induced by UV laser radiation on the blue luminescence of silica nanoparticles L. Spallino a,∗ , L. Vaccaro a , S. Agnello a , M. Cannas a a Dipartimento di Fisica e Chimica, Universit` a di Palermo, Via Archirafi 36, I-90123 Palermo, Italy Abstract The effects induced on the blue luminescence centered around 2.8 eV, char- acteristic 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 re- covery in the post-irradiation stage; 4.66 eV photons cause a total bleaching permanent after the irradiation. These results are interpreted as the conver- sion of luminescent defects towards stable and metastable configurations. Keywords: silica nanoparticles, surface defects, time-resolved photoluminescence, UV laser irradiation, conversion processes 2000 MSC: * Corresponding author Email address: luisa.spallino@unipa.it (L. Spallino ) Preprint submitted to Journal of Luminescence January 15, 2013