Singlet Oxygen Generaion via Silver Nanoparticles UV-Photoexcitation

The NIR-luminescence of silver nanoparticle suspension stabilized in distilled water has been investigated by photoexcitation of surface plasmon resonance (SPR). The observed short-living luminescence with the spectral maximum at 1300 nm is attributed to the singlet oxygen molecules luminescence. The singlet oxygen generation is assumed to pass in two stages as a result of three-photon process. First the one-photon SPR excitation of silver nanoparticle is occurred and leads to superoxide anion generation on the nanoparticle surface. Next the superoxide anion absorbs two more photons of the same laser pulse resulting in electron photodetachment with singlet oxygen formation. During a long period of UV-irradiation the studying suspension ceases to be photostable and sedimentation occurs. The sedimentation may be related to disturbance of nanoparticles steric stabilization resulting in more efficient superoxide anion adsorption on nanoparticles surface with silver oxide formation.