14 research outputs found
Surface Plasmon Enhancement At A Liquid-Metal-Liquid Interface
Herein, we report the first experimental demonstration of surface plasmon enhancement at a liquid-metal-liquid interface using a pseudo-Kretschmann geometry. Pumping gold nanoparticle clusters at the interface of a p-xylene-water mixture, we were able to measure a fluorescence enhancement of three orders of magnitude in Rose Bengal at an excitation wavelength of 532 nm. The observed increase is due to the local electric field enhancement and the reduction of the fluorescence lifetime of dye molecules in the close vicinity of the metal surface. Theoretical modeling using the T-matrix method of the electric field intensity enhancement of emulated surfaces supports the experimental results. This new approach will open a new road for the study of dynamic systems using plasmonics. © Springer Science+Business Media, LLC 2007
Fluorescence Emission Of Disperse Red 1 In Solution At Room Temperature
In this article, we report the fluorescence emission of Disperse Red 1 in solution at room temperature and pumping at 532 nm with a 25 mW diode laser. We have measured its fluorescence quantum yield in methanol, ethylene glycol, glycerol, and phenol obtaining values as high as 10-3 in the aliphatic alcohols. The excitation spectra of Disperse Red 1 in all four solvents as well as its excitation anisotropy in glycerol are presented. Applying a Gaussian decomposition method to the absorption spectra along with the support from the excitation spectra, the positions of the different transitions in this pseudo-stilbene azobenzene dye were determined. Solvatochromic and isomerization constraint effects are discussed. Calculations using density functional theory at TD-B3LYP/6-31G*//HF/6-31G* level were performed to interpret the experimental observations. © 2008 American Chemical Society
Sequestering High-Energy Electrons to Facilitate Photocatalytic Hydrogen Generation in CdSe/CdS Nanocrystals
The photocatalytic H<sub>2</sub>O splitting activities of CdSe and CdSe/CdS core/shell quantum dots are contrasted. CdSe/CdS core/shell quantum dots constructed from 4.0 nm CdSe quantum dots are shown to be strongly active for visible-light-driven photocatalytic H<sub>2</sub> evolution in 0.1 M Na<sub>2</sub>S/Na<sub>2</sub>SO<sub>3</sub> solution with a turnover number of 9.94 after 5 h at 103.9 μmol/h. CdSe quantum dots themselves are only marginally active in 0.1 M Na<sub>2</sub>S/Na<sub>2</sub>SO<sub>3</sub> solution with a turnover number of 1.10 after 5 h at 11.53 μmol/h, while CdSe quantum dots in pure H<sub>2</sub>O are found to be completely inactive. Broad-band transient absorption spectroscopy is used to elucidate the mechanisms that facilitate the enhancement in the CdSe core/shell quantum dots, which is attributed to passivation of surface-deep trap states with energies lying below the reduction potential necessary for H<sub>2</sub>O reduction. Thus, surface trapping dynamics and energetics can be manipulated to dictate the photocatalytic activities of novel CdSe quantum dot based photocatalytic materials
Red States versus Blue States in Colloidal Silicon Nanocrystals: Exciton Sequestration into Low-Density Traps
The ultrafast exciton photodynamics
of red-emitting and blue-emitting
colloidal Si nanocrystals are contrasted under low (1.5 mJ/cm<sup>2</sup>) and high (9.1 mJ/cm<sup>2</sup>) excitation powers with
broadband transient absorption spectroscopy. While the low-power initiated
transient signals differ strongly for the two samples, the high-power
signals exhibit similar nonmonotonic kinetics, resulting in a new
population formed on a 10 to 30-ps time scale with a sample independent
spectrum and decay kinetics. This phenomenon is ascribed to the saturation
of low-density red-emitting and blue-emitting traps via a state-filling
mechanism to populate new meta-stable states at higher excitation
powers. The states responsible for blue emission and high-power populations
are ascribed to traps from low-density nitrogen and oxygen impurities,
respectively, and share similar charge-transfer character with the
silicon nanocrystal core
Chemical Inhomogeneity in the Ultrafast Dynamics of the DXCF Cyanobacteriochrome Tlr0924
Cyanobacteriochromes (CBCRs) are diverse biliprotein
photosensors
distantly related to the red/far-red photoreceptors of the phytochrome
family. There are several subfamilies of CBCRs, displaying varied
spectral responses spanning the entire visible region. Tlr0924 belongs
to the DXCF subfamily that utilizes the Cys residue in a conserved
Asp-Xaa-Cys-Phe (DXCF) motif to form a second covalent linkage to
the chromophore, resulting in a blue-absorbing dark state. Photoconversion
leads to elimination of this linkage, resulting in a green-absorbing
photoproduct. Tlr0924 initially incorporates phycocyanobilin (PCB)
as a chromophore, exhibiting a blue/orange photocycle, but slowly
isomerizes PCB to phycoviolobilin (PVB) to yield a blue/green photocycle.
Ultrafast transient absorption spectroscopy was used to study both
forward and reverse reaction photodynamics of the recombinant GAF
domain of Tlr0924. Primary photoproducts were identified, as were
subsequent intermediates at 1 ms. PCB and PVB population photodynamics
were decomposed using global target analysis. PCB and PVB populations
exhibit similar and parallel photocycles in Tlr0924, but the PVB population
exhibits faster excited-state decay in both reaction directions. On
the basis of longer time analysis, we show that the photochemical
coordinate (15,16-isomerization) and second-linkage coordinate (elimination
or bond formation at C10) are separate processes in both directions