The Formation of "Hot Spots" in Mesoporous TiO 2 Films by Photodeposited Silver Nanoparticles for Use in Nonlinear Optical Spectroscopy of Isolated Molecules

The excitation of silver photocatalytically deposited on the surface of TiO 2 nanoparticles that formed a mesoporous film with femtosecond titanium-sapphire laser pulses caused two-photon luminescence of silver clusters. Luminescence was detected by scanning laser spectroscopy as "hot spots." The system with silver on TiO 2 had a high concentration of luminescing silver nanoparticles, which were fairly stable to degra- dation at long exposures. It was assumed that the high concentration of luminescing spots was caused by a high concentration of localized surface plasmons in the Ag/TiO 2 system. The Ag/TiO 2 system therefore offers prom- ise for use in the spectroscopy of isolated molecules and visualization of biological objects.