@article {849,
	title = {Determination of the localization times of electrons and holes in the HgS well in a CdS/HgS/CdS quantum dot{\textendash}quantum well nanoparticle},
	journal = {Physical Review BPhys. Rev. B},
	volume = {66},
	year = {2002},
	month = {2002/11/11/},
	pages = {205312 - },
	publisher = {American Physical Society},
	abstract = {The femtosecond time-resolved electron-hole dynamics of the CdS/HgS/CdS quantum dot{\textendash}quantum well system (QDQW) was investigated as a function of excitation energy. In the transient absorption spectra four bleach bands and a stimulated emission signal in the visible spectral range between 450 and 780 nm were resolved. By using an IR probe pulse at 4.7 μm a transient induced absorption due to intraband transitions was found. The decay and rise times of these signals were measured when the CdS core or the HgS well of the nanoparticles was excited by the pump pulse. After excitation within the HgS well the transient signals rise within the resolution of our pump pulse, while after core excitation slower rise times were measured. From the 1.5 ps rise time of the stimulated emission originating from the HgS well and the intraband hole IR absorption (150 fs) after excitation into the CdS core, the electron localization time (transfer time from the core to the well) is found to be 1.5 ps while that of the hole is \~{}150 fs. This large difference in the observed dynamics of the electron and hole in crossing the CdS/HgS interface is discussed.},
	doi = {10.1103/PhysRevB.66.205312 },
	url = {http://link.aps.org/doi/10.1103/PhysRevB.66.205312},
	author = {Braun, Markus and Link, Stephan and Burda, Clemens and El-Sayed, Mostafa A}
}
@article {1202,
	title = {The effect of surface adsorption on the hyper-Rayleigh scattering of large and small CdSe nanoparticles},
	journal = {Chemical Physics Letters},
	volume = {363},
	number = {5-6},
	year = {2002},
	note = {Landes, C Braun, M El-Sayed, MA},
	month = {Sep},
	pages = {465-470},
	abstract = {Hyper-Rayleigh scattering is used to compare the effect of the addition of n-butylamine to large (3.2 nm) and small (1.6 nm) Use nanoparticles (NPs). It is found that although the adsorption of n-butylamine on large NPs enhances their nonlinear optical response, it has the opposite effect when adsorbed on the small nanoparticles for which the amine adsorption was found previously to induce structural changes. This observation is consistent with an increase in the symmetry of the nanocrystal structure such as would be observed in a phase change from a 4-coordinate wurtzite crystal structure to that of a 6-coordinate zinc-blend form. (C) 2002 Published by Elsevier Science B.V.},
	isbn = {0009-2614},
	doi = {10.1016/s0009-2614(02)01169-7},
	author = {Landes, Christy F. and Braun, Markus and El-Sayed, Mostafa A}
}
@article {1195,
	title = {The quenching of CdSe quantum dots photoluminescence by gold nanoparticles in solution},
	journal = {Photochemistry and Photobiology},
	volume = {75},
	number = {6},
	year = {2002},
	note = {Nikoobakht, B Burda, C Braun, M Hun, M El-Sayed, MA},
	month = {Jun},
	pages = {591-597},
	abstract = {The photoluminescence (PL) of CdSe quantum dots (QD) in aqueous media has been studied in the presence of gold nanoparticles (NP) with different shapes. The steady state PL intensity of CdSe QD (1.5-2 nm in size) is quenched in the presence of gold NP. Picosecond bleach recovery and nanosecond time-resolved luminescence measurements show a faster bleach recovery and decrease in the lifetime of the emitting states of CdSe QD in the presence of quenchers. Surfactant-capped gold nanorods (NR) with aspect ratio of 3 and surfactant-capped and citrate-capped nanospheres (NS) of 12 nm diameter were used as quenchers in order to study the effect of shape and surface charge on the quenching rates. The Stern-Volmer kinetics model is used to examine the observed quenching behavior as a function of the quencher concentration. It was found that the quenching rate of NR is more than 1000 times stronger than that of NS with the same capping material. We also found that the quenching rate decreases as the length of the NR decreases, although the overlap between the CdSe emission and the NR absorption increases. This suggests that the quenching is a result of electron transfer rather than long-range (Forster-type) energy transfer processes. The quenching was attributed to the transfer of electron with energies below the Fermi level of gold to the trap holes of CdSe QD. The observed large difference between NR and NS quenching efficiencies was attributed to the presence of the {110} facets only in the NR, which have higher surface energy.},
	isbn = {0031-8655},
	doi = {10.1562/0031-8655(2002)075<0591:tqocqd>2.0.co;2},
	author = {Nikoobakht, Babak and Burda, Clemens and Braun, Markus and Hun, M. and El-Sayed, Mostafa A}
}
@article {854,
	title = {Transfer times of electrons and holes across the interface in CdS/HgS/CdS quantum dot quantum well nanoparticles},
	journal = {Chemical physics letters},
	volume = {361},
	year = {2002},
	pages = {446-452},
	publisher = {Elsevier},
	abstract = {The electron and hole trapping times in the HgS well of a 6 nm CdS/HgS/CdS quantum dot quantum well nanoparticle were determined from the rise time of the ultrafast transient absorption in the visible and IR regions as well as the trap fluorescence when the CdS core is excited. From the 1.5 ps observed rise time of the well fluorescence (which is determined by the trapping time of the slowest carrier) and the intraband hole IR absorption (150 fs), the electron localization time is found to be 1.5 ps while that of the hole is \~{}150 fs. This large difference in the observed dynamics of the electron and hole in crossing the CdS/HgS interface is discussed.},
	isbn = {0009-2614},
	doi = {10.1016/S0009-2614(02)01001-1 },
	url = {http://dx.doi.org/10.1016/S0009-2614(02)01001-1 },
	author = {Braun, Markus and Link, Stephan and Burda, Clemens and El-Sayed, Mostafa A}
}
@article {1210,
	title = {Hot electron and phonon dynamics of gold nanoparticles embedded in a gel matrix},
	journal = {Chemical Physics Letters},
	volume = {343},
	number = {1-2},
	year = {2001},
	note = {Mohamed, MB Ahmadi, TS Link, S Braun, M El-Sayed, MA},
	month = {Jul},
	pages = {55-63},
	abstract = {Using pump-probe technique, the dynamics of the hot carriers in metallic nanodots induced by femtosecond laser pulses are investigated in gold nanoparticles embedded in hydrogel and in organic gel and compared to that in aqueous solution. We found that changing the surrounding matrix from aqueous solution to hydrogel and then to organic gel leads to a large increase in the relaxation time of both the electron-phonon (e-ph) and the phonon-phonon (ph-ph) coupling. Furthermore, the ph-ph relaxation time becomes sensitive to the type of the organic solvent trapped in the gel network. This indicates that the relaxation dynamics depend on the thermal conductivity, chemical structure and the molecular dynamics of the surrounding medium. (C) 2001 Elsevier Science BN. All rights reserved.},
	isbn = {0009-2614},
	doi = {10.1016/s0009-2614(01)00653-4},
	author = {Mohamed, MB and Ahmadi, Temer S. and Link, Stephan and Braun, Markus and El-Sayed, Mostafa A}
}
@article {855,
	title = {On the Nanoparticle to Molecular Size Transition:  Fluorescence Quenching Studies},
	journal = {The Journal of Physical Chemistry B},
	volume = {105},
	year = {2001},
	note = {doi: 10.1021/jp0118726},
	month = {2001},
	pages = {10554 - 10558},
	publisher = {American Chemical Society},
	abstract = {Semiconductor nanoparticles, NPs, exhibit fluorescence properties that are closely related to the nature of their surface. CdSe NPs that range in size from 2 to 15 nm in diameter fluoresce with both near-band-edge emission and deep-trap emission, depending on the quality of the surface. When butylamine is added to colloidal solutions of NPs in this size range, the amine is thought to bind to the NP surface and eliminate radiant recombination pathways that lead to luminescence. Since the amine binds to the NP surface, the decrease in fluorescence intensity does not follow standard molecular models of collisional fluorescence quenching. NPs that are smaller than ?2 nm are composed entirely of a discontinuous arrangement of atoms that are all in constant chemical contact with capping material, solvent, and contaminants. When butylamine is added to solutions of these smaller NPs, the fluorescence quenching follows more standard collisional quenching models. Thus, by monitoring the interaction between NPs and a hole acceptor such as butylamine, one can observe the transition from NP, with atoms both in the core and on the surface, to molecular cluster, with no core atoms to dominate the electron density, but with only surface atoms that can participate in molecular processes such as electron transfer.Semiconductor nanoparticles, NPs, exhibit fluorescence properties that are closely related to the nature of their surface. CdSe NPs that range in size from 2 to 15 nm in diameter fluoresce with both near-band-edge emission and deep-trap emission, depending on the quality of the surface. When butylamine is added to colloidal solutions of NPs in this size range, the amine is thought to bind to the NP surface and eliminate radiant recombination pathways that lead to luminescence. Since the amine binds to the NP surface, the decrease in fluorescence intensity does not follow standard molecular models of collisional fluorescence quenching. NPs that are smaller than ?2 nm are composed entirely of a discontinuous arrangement of atoms that are all in constant chemical contact with capping material, solvent, and contaminants. When butylamine is added to solutions of these smaller NPs, the fluorescence quenching follows more standard collisional quenching models. Thus, by monitoring the interaction between NPs and a hole acceptor such as butylamine, one can observe the transition from NP, with atoms both in the core and on the surface, to molecular cluster, with no core atoms to dominate the electron density, but with only surface atoms that can participate in molecular processes such as electron transfer.},
	isbn = {1520-6106},
	url = {http://dx.doi.org/10.1021/jp0118726},
	author = {Landes, Christy F. and Braun, Markus and El-Sayed, Mostafa A}
}
@article {1216,
	title = {Observation of large changes in the band gap absorption energy of small CdSe nanoparticles induced by the adsorption of a strong hole acceptor},
	journal = {Nano Letters},
	volume = {1},
	number = {11},
	year = {2001},
	note = {Landes, C Braun, M Burda, C El-Sayed, MA},
	month = {Nov},
	pages = {667-670},
	abstract = {When butylamine In relatively high concentrations (0.1-0.25 M) is added to a colloidal solution of CdSe nanoparticles (NPs) that are approximately 1.6 nm in diameter, the band gap absorption changes from a broad, relatively weak absorption centered at 445 nm to a narrow, relatively strong absorption centered at 414 nm. The effect of concentration on the observed spectrum shows an isobestic point, suggesting an equilibrium between two species. The possible mechanisms for such a transformation are discussed.},
	isbn = {1530-6984},
	doi = {10.1021/nl015619t},
	author = {Landes, Christy F. and Braun, Markus and Burda, Clemens and El-Sayed, Mostafa A}
}
@article {1215,
	title = {Photoluminescence of CdSe nanoparticles in the presence of a hole acceptor: n-butylamine},
	journal = {Journal of Physical Chemistry B},
	volume = {105},
	number = {15},
	year = {2001},
	note = {Landes, C Burda, C Braun, M El-Sayed, MA},
	month = {Apr},
	pages = {2981-2986},
	abstract = {Addition of butylamine to a solution of colloidal CdSe nanoparticles (NPs) caused a decrease in fluorescence intensity, with no effect on the picosecond bleach recovery of the exciton formation or on the luminescence dynamics. The relative fluorescence quantum yield was found to decrease with increasing butylamine concentration and to level off at high concentrations, but the fluorescence lifetimes were not influenced. The nonlinear concentration dependence of the fluorescence quantum yield did not follow the Stern-Volmer equation. This is in agreement with the observation that the CdSe luminescence lifetime was not affected by the addition of butylamine. A mechanism is proposed in which the emission observed in CdSe is assumed to result from the combination of surface-trapped electrons and holes. n-Butylamine occupies hole sites, thus blocking the recombination process, which results in decreasing the density of luminescent centers. These results will be discussed in terms of the nature of the binding sites of the amine on the nanoparticle surface.},
	isbn = {1089-5647},
	doi = {10.1021/jp0041050},
	author = {Landes, Christy F. and Burda, Clemens and Braun, Markus and El-Sayed, Mostafa A}
}
@article {1211,
	title = {The relaxation dynamics of the excited electronic states of retinal in bacteriorhodopsin by two-pump-probe femtosecond studies},
	journal = {Proceedings of the National Academy of Sciences of the United States of America},
	volume = {98},
	number = {15},
	year = {2001},
	note = {Logunov, SL Volkov, VV Braun, M El-Sayed, MA},
	month = {Jul},
	pages = {8475-8479},
	abstract = {We present the results of two-pump and probe femtosecond experiments designed to follow the relaxation dynamics of the lowest excited state (S-1) populated by different modes. In the first mode, a direct (S-0 --> S-1) radiative excitation of the ground state is used. In the second mode, an indirect excitation is used where the S-1 state is populated by the use of two femtosecond laser pulses with different colors and delay times between them. The first pulse excites the S-0 --> S-1 transition whereas the second pulse excites the S-1 --> S-n transition. The nonradiative relaxation from the S-n state populates the lowest excited state. Our results suggest that the S1 state relaxes faster when populated nonradiatively from the S-n state than when pumped directly by the S-0 --> S-1 excitation. Additionally, the S-n --> S-1 nonradiative relaxation time is found to change by varying the delay time between the two pump pulses. The observed dependence of the lowest excited state population as well as its dependence on the delay between the two pump pulses are found to fit a kinetic model in which the S-n state populates a different surface (called Si) than the one being directly excited (S-1). The possible involvement of the A(g) type states, the J intermediate, and the conical intersection leading to the S-0 or to the isomerization product (K intermediate) are discussed in the framework of the proposed model.},
	isbn = {0027-8424},
	doi = {10.1073/pnas.141220198},
	author = {Logunov, Stephan L. and Volkov, V. V. and Braun, Markus and El-Sayed, Mostafa A}
}
@article {1219,
	title = {Variation of the thickness and number of wells in the CdS/HgS/CdS quantum dot quantum well system},
	journal = {Journal of Physical Chemistry A},
	volume = {105},
	number = {23},
	year = {2001},
	note = {Braun, M Burda, C El-Sayed, MA},
	month = {Jun},
	pages = {5548-5551},
	abstract = {We report on the first chemically prepared multilayer quantum well structure in a semiconductor quantum dot. By subsequent precipitation of HgS, CdS, HgS, and again CdS from aqueous solution, we obtained nanoparticles which contain two HBS quantum wells separated by a double layer of CdS. The:core:and the capping material is also CdS. The two-well system was characterized by absorption and emission spectroscopy, which clearly reveal the formation of a two-well and not a single double-layered quantum well system. This system allows to study the interaction of quantum wells that are separated by different thicknesses of the CdS barriers. The radiative and relaxation dynamics of the new two-well system are compared with the dynamics of systems having a single-layer well and a double-layer well system.},
	isbn = {1089-5639},
	doi = {10.1021/jp010002l},
	author = {Braun, Markus and Burda, Clemens and El-Sayed, Mostafa A}
}
