We investigate the interface between core and shell in zinc blende CdSebased CdSe/CdS dot-in-dot heteronanocrystals. Using X-ray diffraction and transmission electron microscopy, we show that a CdS shell grows coherently around the CdSe core. A comparison of the Raman spectrum of bare CdSe nanocrystals and CdSe/CdS heteronanocrystals indicates that the difference in lattice constant leads to compressive and tensile strain in core and shell, respectively. Concomitant continuum mechanical calculations follow this result, yet the calculated strain exceeds the experimental values. Moreover, a detailed analysis of the CdSe/CdS Raman spectra reveals the appearance of additional features upon shell growth. A comparison with pure Cd(Se,S) alloyed nanocrystals relates these features to alloy vibrations. We show that these observations point toward the presence of a mixed Cd(Se,S) layer at the CdSe/CdS interface. In this way, this work provides an experimental framework based on Raman spectroscopy to analyze in detail interfacial alloying in heteronanocrystals.

The resonance Raman (RR) spectra of beta-carotene have been studied in solution and in the protein complexes of photosystems I and II (PS I, PS II). The experimental studies are complemented by density functional theory (DFT) calculations that allow for a consistent assignment of most of the experimental RR bands in the region between 900 and 1650 cm(-1). Thus, it was shown that the prominent peak at ca. 1525 cm(-1) is composed of two closely spaced modes, both of which dominated by C=C stretching coordinates of the polyene chain. These two modes exhibit different excitation profiles in the region of the allowed electronic S(0) --> S(2) transition with maxima that are separated by ca. 1300 cm(-1). Calculated RR spectra and excitation profiles obtained by time-dependent DFT in conjunction with the transform method indicate that the enhancement pattern of these modes cannot be rationalised within the Condon approximation (A-term scattering). Furthermore, symmetry considerations rule out enhancement via vibronic coupling. Instead, we suggest that the different excitation profiles of the two modes result from force constant changes and mode mixing upon electronic transition (Dushinsky rotation). RR spectra and excitation profiles are very similar in solution and in the protein complexes. Thus, the excitation-dependent frequency variation of the 1525-cm(-1) peak in PS I and PS II is an intrinsic molecular property of beta-carotene and does not reflect different pools of the pigments in specific molecular environments.

In the present work we have studied β ‐carotene dissolved in dichloromethane by means of resonance Raman spectroscopy. To obtain the Raman excitation profiles Raman spectra of β ‐carotene have been acquired at various wavelengths throughout the visible region. It was found that the position of the prominent peak at ca. 1524 cm–1 varies with the excitation wavelength indicating the involvement of two different modes. Possible origins of the different enhancement pattern of the two modes are discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We have studied the resonance Raman spectra of b-carotene in solution and in protein-complexes using laser excitation at various wavelengths in the visible region. Main focus was laid on the n 1 -band, which shows an anomalous behaviour upon variation of the excitation wavelength resulting in a frequency shift of the peak maximum. This shift is due to different excitation profiles of two closely spaced modes as shown previously for b-carotene in solution. In this work, we have extended the studies to the antenna pigment in photosystems I and II (PS I and PS II).

We studied the evolution of Raman signals stemming from colloidal PbTe/CdTe nanocrystals (NCs). The NCs were grown using the cation exchange method and samples having different amounts of CdTe as shell material were investigated. The observed Raman bands are correlated to pure tellurium modes and after introduction of CdTe its longitudinal optical (LO) mode becomes also visible. The tellurium modes' intensity rapidly decreases after cationic exchange due to the chemical bonding of the vacant tellurium atoms.