title: UV induced local heating effects in TiO2 nanocrystals.
abstract: When isolated TiO(2) nanocrystals are subjected to UV light at 77 K and pressures below 10(-6) mbar, trapping of photogenerated hole centers occurs on the surface of the nanocrystals and can be tracked by time-resolved electron paramagnetic resonance spectroscopy. Irrespective of the selected UV irradiance used, the maximum concentration of trapped charges was found to be constant for a given number of nanocrystals ( approximately 10(15)) and corresponds to one electron-hole pair per particle. On a time scale of seconds to minutes the dynamics for the trapping process depend on the number of photons with supra band gap energy. A local temperature rise of the TiO(2) nanocrystals was observed for irradiances above 1.55 mW cm(-2) (10(15) photons cm(-2) s(-1)). This is attributed to enhanced nonradiative recombination of photogenerated charge carriers via heat production and points to a substantial contribution of thermal chemistry in photocatalytic reaction cycles.
authors.affiliation: Institut für Materialchemie, Technische Universität Wien, Veterinärplatz 1/GA, Vienna A-1210, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Berger
authors.forename: Oliver
authors.initials: O
authors.lastname: Diwald
authors.forename: Erich
authors.initials: E
authors.lastname: Knözinger
authors.forename: Martin
authors.initials: M
authors.lastname: Sterrer
authors.forename: John T
authors.initials: JT
authors.lastname: Yates
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D006358:Hot Temperature; D049329:Nanostructures / Q000737:chemistry* / Q000528:radiation effects; D014025:Titanium / Q000737:chemistry* / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: C009495:titanium dioxide; D014025:Titanium