Spectroscopy and femtosecond dynamics of type-II CdSe/ZnTe core-shell semiconductor synthesized via the CdO precursor

Journal of Physical Chemistry B - J PHYS CHEM B 06/2004; 108(30). DOI: 10.1021/jp049177w

ABSTRACT CdSe/ZnTe type-II quantum dots (QDs) synthesized via the CdO precursor are reported. Spectroscopic and femtosecond dynamic measurements reveal that the rate of photoinduced electron/hole spatial separation decreases with increases in the size of the core, and it is independent of the thickness of the shell in the CdSe/ZnTe QDs. The results are consistent with the binding strength of the electron and hole confined at the center of CdSe. The correlation between the core/shell size and the electron/hole spatial separation rate resolved in this study may provide valuable information for applications where rapid photoinduced carrier separation followed by charge transfer into a matrix or electrode is crucial, such as in photovoltaic devices.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Oligothiophenes incorporating MM quadruple bonds have been prepared from the reactions between Mo(2)(TiPB)(4) (TiPB = 2,4,6-triisopropyl benzoate) and 3',4'-dihexyl-2,2'-:5',2''-terthiophene-5,5''-dicarboxylic acid. The oligomers of empirical formula Mo(2)(TiPB)(2)(O(2)C(Th)-C(4)(n-hexyl)(2)S-(Th)CO(2)) are soluble in THF and form thin films with spin-coating (Th = thiophene). The reactions between Mo(2)(TiPB)(4) and 2-thienylcarboxylic acid (Th-H), 2,2'-bithiophene-5-carboxylic acid (BTh-H), and (2,2':5',2''-terthiophene)-5-carboxylic acid (TTh-H) yield compounds of formula trans-Mo(2)(TiPB)(2)L(2), where L = Th, BTh, and TTh (the corresponding thienylcarboxylate), and these compounds are considered as models for the aforementioned oligomers. In all cases, the thienyl groups are substituted or coupled at the 2,5 positions. Based on the x-ray analysis, the molecular structure of trans-Mo(2)(TiPB)(2)(BTh)(2) reveals an extended Lpi-M(2)delta-Lpi conjugation. Calculations of the electronic structures on model compounds, in which the TiPB are substituted by formate ligands, reveal that the HOMO is mainly attributed to the M(2)delta orbital, which is stabilized by back-bonding to one of the thienylcarboxylate pi* combinations, and the LUMO is an in-phase combination of the thienylcarboxylate pi* orbitals. The compounds and the oligomers are intensely colored due to M(2)delta-thienyl carboxylate pi* charge transfer transitions that fall in the visible region of the spectrum. For the molybdenum complexes and their oligomers, the photophysical properties have been studied by steady-state absorption spectroscopy and emission spectroscopy, together with time-resolved emission and transient absorption for the determination of relaxation dynamics. Remarkably, THF solutions the molybdenum complexes show room-temperature dual emission, fluorescence and phosphorescence, originating mainly from (1)MLCT and (3)MM(deltadelta*) states, respectively. With increasing number of thienyl rings from 1 to 3, the observed lifetimes of the (1)MLCT state increase from 4 to 12 ps, while the phosphorescence lifetimes are approximately 80 micros. The oligomers show similar photophysical properties as the corresponding monomers in THF but have notably longer-lived triplet states, approximately 200 micros in thin films. These results, when compared with metallated oligothiophenes of the later transition elements, reveal that M(2)delta-thienyl pi conjugation leads to a very small energy gap between the (1)MLCT and (3)MLCT states of <0.6 eV.
    Proceedings of the National Academy of Sciences 10/2008; 105(40):15247-52. · 9.81 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: It is widely accepted that the nanomaterials with the most promise for industrial photo-catalytic hydrogen production are prone to disabling photo-corrosion through anodic oxidation upon illumination in aqueous environments. Steps must be taken to either arrest the photo-oxidation of these particular materials, or to develop suitable alternatives which would provide sufficient photo-catalytic activity for industrial purposes. This review article addresses the background of photolytic hydrogen production from water, and examines the theory and current level of research aimed at overcoming semiconductor photo-corrosion. It should be noted that this review does not seek to present technical knowledge outlining synthesis methods or photo-catalytic libraries, rather to outline the recent efforts in semiconductor based nano-systems, being inert metal coatings, Z-schemes, doping of UV-absorbing metal-oxides, and dimensional nanorod structures.
    International Journal of Hydrogen Energy 09/2009; 34(18):7562-7578. · 3.55 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This review focuses on the efficiency of different nanomaterials used in photocatalytic hydrogen production. Some 200 articles were reviewed for photocatalytic hydrogen production (liquid and gas phase) in a random review of photocatalysts for both water and H2S splitting. The photocatalytic reactors used for both liquid- and gas-phase hydrogen production are also discussed. Among the photocatalysts used, nanosized photocatalyts have a much greater surface area and thus give a better hydrogen yield than microsized photocatalysts.
    Materials Science in Semiconductor Processing 04/2013; · 1.34 Impact Factor


Available from