Spectroscopic properties of trapped electrons on the surface of MgO nanoparticles.
To characterise electron-trapping sites on the surface of MgO nanoparticles, surface colour centres were generated using UV light in conjunction with selected hydrogen-based electron sources. Four different colour-centre species, including the characteristic (e-)(H+) or F(S)+(H) centre, were identified due to the distinct shape of the respective electron paramagnetic resonance (EPR) signals. The analysis of the EPR saturation behaviour down to microwave powers of 5 x 10(-3) mW reveals an enhanced spin-relaxation probability of the (e-)(H+) centre compared to all other F(S)+ centres that do not exhibit significant magnetic interactions with hydroxylic protons. Beside the dipolar magnetic interaction in the (e-)(H+) centre observed by EPR, the electronic interaction between the unpaired electron and the proton of a closely spaced OH group produces a redshift of the OH stretching band by about 70 to 170 cm(-1), as observed by infrared spectroscopy. EPR and IR spectroscopic data obtained after the selective address of individual reaction channels for surface colour-centre formation point to the fact that (e-)(H+) centres are formed by trapping electrons from H atoms. Consequently, the underlying surface defect does not belong to the sites of the MgO surface, which chemisorb hydrogen via a heterolytic splitting process.
Sterrer
Martin
M
Institut für Materialchemie, Technische Universität Wien, Veterinärplatz 1/GA, 1210 Wien, Austria.
Berger
Thomas
T
Stankic
Slavica
S
Diwald
Oliver
O
Knözinger
Erich
E
D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D004583:Electrons; D006859:Hydrogen / Q000737:chemistry / Q000528:radiation effects; D008277:Magnesium Oxide / Q000737:chemistry* / Q000528:radiation effects; D049329:Nanostructures / Q000737:chemistry*; D010084:Oxidation-Reduction; D011522:Protons; D013499:Surface Properties; D014466:Ultraviolet Rays
D011522:Protons; D008277:Magnesium Oxide; D006859:Hydrogen