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The pump power dependence of the femtosecond relaxation of CdSe nanoparticles observed in the spectral range from visible to infrared (2002)

Burda, Clemens ; Link, Stephan ; Mohamed, Mona B. ; [et al.]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 116 (2002), S. 3828-3833

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: The pump power dependence of the relaxation dynamics of CdSe nanoparticles (NPs) was studied with femtosecond pump probe spectroscopy at observation wavelengths of the first exciton transition at 560 nm, the near infrared (NIR) absorption at 2 μm, and the transient mid-infrared (IR) absorption at 4.5 μm. Excitation with less than one photon per particle leads to bleaching of the excitonic transitions, and the bleach intensity is initially linear to the pump power. At higher pump power the bleach intensity levels off, when complete saturation of the excitonic transition is reached. At the same time, increasing pump power causes an acceleration of the bleach decay, which is due to additional Auger processes when multiple excitons are formed in the NPs. In addition, the pump power effect was investigated for the NIR and IR regions, at 2 and 4.5 μm wavelength, respectively. Whereas the IR transients are very similar to the ones observed for the bleach, the NIR transients behave completely different. No pump power dependence was found for the transients at 2 μm when pumped in a power range from 0.5 to 5 μJ per pulse. The results show that the fs transients in the visible (bleach) and IR (absorption) regions are due to electron relaxation in the conduction band and the NIR transients are due to the relaxation of the hole. Furthermore, it suggests that in the investigated CdSe NPs, Auger processes act much more efficiently on the electrons than for the holes. © 2002 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1446851

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Radical Anions of Polyalkylazulenes: An ESR and ENDOR Study (1994)

Bachmann, Rainer ; Burda, Clemens ; Gerson, Fabian ; [et al.]

New York, NY : Wiley-Blackwell

Helvetica Chimica Acta 77 (1994), S. 1458-1465

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ISSN: 0018-019X

Keywords: Chemistry ; Organic Chemistry

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: Proton-hyperfine data are reported for the radical anions generated from azulene (1) and its alkyl derivatives 2-11 in 1,2-dimethoxyethane both ‘chemically’ with K and electrolytically. The alkyl derivatives are 1,3-dimethyl- (2), 5,7-dimethyl- (3), 1,3,5,7-tetramethyl- (4), 2-methyl- (5), 4,6,8-trimethyl- (6), 2,4,6,8-tetramethyl-(7), 1,3,4,6,8-pentamethyl- (8), 1,3,4,8-tetramethyl-6-propyl- (9), 6-(tert-butyl)-1,3,4,8-tetramethyl- (10), and 1,2,3,4,6,8-hexamethylazulene (11). Alkyl substituents at the odd-numbered centers μ = 1, 3, 5, and 7 partly shift the π-spin population from the seven- to the five-membered ring, whereas those at the even-numbered centers μ = 4, 6, and 8 exert an opposite effect on the π-spin distribution.

Additional Material: 4 Ill.