@article{Besemann2004, author = {Besemann, Daniel M. and Meyer, Kent A. and Wright, John C.}, title = {{Spectroscopic Characteristics of Triply Vibrationally Enhanced Four-Wave Mixing Spectroscopy †}}, journal = {The Journal of Physical Chemistry B}, volume = 108, number = 29, pages = {10493--10504}, year = 2004, doi = {10.1021/jp049597l}, url = {http://pubs.acs.org/doi/abs/10.1021/jp049597l}, abstract = {Triply vibrationally enhanced (TRIVE) four-wave mixing is a fully resonant, frequency domain spectroscopy that is capable of coherent multidimensional vibrational spectroscopy. TRIVE has 12 different coherence pathways that differ in their time ordering and resonances. The pathways are the coherent analogue to two-color pump-probe pathways. Specific pathways or sets of pathways can be chosen by appropriate selection of time delays and resonance conditions. The pathways have characteristic positions and line shapes in three-dimensional frequency space and their coherent interference has consequences in interpreting the spectra. The line shapes and the relative intensities of different pathways are dependent on the population relaxation and dephasing rates. The different pathways also have different capabilities for line-narrowing inhomogeneously broadened transitions. The narrowing is controlled by the interference between pathways and the quantum level interference between different parts of the inhomogeneously broadened envelope. We also show that selection of the output frequency in two-color TRIVE methods constrains the selection rules that control the relative transition probabilities of the four transitions.}, file = {::}, issn = {1520-6106}, month = {jul}, } @article{Block2012, author = {Block, Stephen B. and Yurs, Lena a. and Pakoulev, Andrei V. and Selinsky, Rachel Sarah and Jin, Song and Wright, John C.}, title = {{Multiresonant Multidimensional Spectroscopy of Surface-Trapped Excitons in PbSe Quantum Dots}}, journal = {The Journal of Physical Chemistry Letters}, volume = 3, number = 18, pages = {2707--2712}, year = 2012, doi = {10.1021/jz300599b}, url = {http://pubs.acs.org/doi/abs/10.1021/jz300599b}, file = {::}, issn = {1948-7185}, month = {sep}, } @article{BritoCruz1988, author = {{Brito Cruz}, C.H. and Gordon, J.P. and Becker, P.C. and Fork, R.L. and Shank, C.V.}, title = {{Dynamics of spectral hole burning}}, journal = {IEEE Journal of Quantum Electronics}, volume = 24, number = 2, pages = {261--269}, year = 1988, doi = {10.1109/3.122}, url = {http://ieeexplore.ieee.org/document/122/}, file = {::}, issn = {0018-9197}, month = {feb}, } @article{Carlson1989, author = {Carlson, Roger J. and Wright, John C.}, title = {{Absorption and Coherent Interference Effects in Multiply Resonant Four-Wave Mixing Spectroscopy}}, journal = {Applied Spectroscopy}, volume = 43, number = 7, pages = {1195--1208}, year = 1989, doi = {10.1366/0003702894203408}, url = {http://openurl.ingenta.com/content/xref?genre=article{\&}issn=0003-7028{\&}volume=43{\&}issue=7{\&}spage=1195}, abstract = {The effects of coherent interference between resonant and nonresonant signals and the effects of absorption on multiresonant four-wave mixing spectra are investigated both theoretically and experimentally in azu- iene-doped naphthalene crystals at 2 K. Both effects can strongly alter line shapes and intensities. Line splittings and negative spectral features are demonstrated. Coherent interference, although measurable in this system, is weak. Absorption, however, plays an important role, and its effects on phase matching, peak shapes, and peak intensities are pre- dicted theoretically and are confirmed by the experimental measure- ments. A new expression for the four-wave mixing is derived in terms of sample absorption coefficients and absorption cross sections, and gen- eral conditions for maximum efficiency are determined.}, file = {::}, issn = 00037028, keywords = {M-factors}, mendeley-tags ={M-factors}, month = {sep}, } @article{Czech2015, author = {Czech, Kyle J. and Thompson, Blaise J. and Kain, Schuyler and Ding, Qi and Shearer, Melinda J. and Hamers, Robert J. and Jin, Song and Wright, John C.}, title = {{Measurement of Ultrafast Excitonic Dynamics of Few-Layer MoS 2 Using State-Selective Coherent Multidimensional Spectroscopy}}, journal = {ACS Nano}, volume = 9, number = 12, pages = {12146--12157}, year = 2015, doi = {10.1021/acsnano.5b05198}, url = {http://pubs.acs.org/doi/abs/10.1021/acsnano.5b05198}, abstract = {We report the first coherent multidimensional spectroscopy study of a MoS2 film. A four-layer sample of MoS2 was synthesized on a silica substrate by a simplified sulfidation reaction and characterized by absorption and Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. State-selective coherent multidimensional spectroscopy (CMDS) on the as-prepared MoS2 film resolved the dynamics of a series of diagonal and cross-peak features involving the spin-orbit split A and B excitonic states and continuum states. The spectra are characterized by striped features that are similar to those observed in CMDS studies of quantum wells where the continuum states contribute strongly to the initial excitation of both the diagonal and cross-peak features, while the A and B excitonic states contributed strongly to the final output signal. The strong contribution from the continuum states to the initial excitation shows that the continuum states are coupled to the A and B excitonic states and that fast intraband relaxation is occurring on a sub-70 fs time scale. A comparison of the CMDS excitation signal and the absorption spectrum shows that the relative importance of the continuum states is determined primarily by their absorption strength. Diagonal and cross-peak features decay with a 680 fs time constant characteristic of exciton recombination and/or trapping. The short time dynamics are complicated by coherent and partially coherent pathways that become important when the excitation pulses are temporally overlapped. In this region, the coherent dynamics create diagonal features involving both the excitonic states and continuum states, while the partially coherent pathways contribute to cross-peak features.}, file = {::}, issn = {1936-0851}, keywords = {2D,2d,are layered,molybdenum sul fi de,molybdenum sulfide,multidimensional,nonlinear,ransition metal dichalcogenides,semiconductors with strong spin,such as mos 2,tmdcs,transition metal dichalcogenides,ultrafast dynamics,{\`{a}}}, month = {dec}, pmid = 26525496, } @article{Dai2009, author = {Dai, Quanqin and Wang, Yingnan Yiding and Li, Xinbi and Zhang, Yu and Pellegrino, Donald J. and Zhao, Muxun and Zou, Bo and Seo, JaeTae and Wang, Yingnan Yiding and Yu, William W.}, title = {{Size-dependent composition and molar extinction coefficient of PbSe semiconductor nanocrystals.}}, journal = {ACS nano}, volume = 3, number = 6, pages = {1518--24}, year = 2009, doi = {10.1021/nn9001616}, url = {http://www.ncbi.nlm.nih.gov/pubmed/19702314}, abstract = {Atomic compositions and molar extinction coefficients of PbSe semiconductor nanocrystals were determined by atomic absorption spectrometry, UV-vis-NIR spectrophotometry, and transmission electron microscopy. The Pb/Se atomic ratio was found to be size-dependent with a systematic excess of Pb atoms in the PbSe nanocrystal system. Experimental results indicated that the individual PbSe nanocrystal was nonstoichiometric, consisting of a PbSe core and an extra layer of Pb atoms. For these nonstoichiometric PbSe semiconductor nanocrystals, we proposed a new computational approach to calculate the total number of Pb and Se atoms in different sized particles. This calculation played a key role on the accurate determination of the strongly size-dependent extinction coefficient, which followed a power law with an exponent of approximately 2.5.}, file = {::}, isbn = {1936-0851}, issn = {1936-086X}, keywords = {Composition,Molar extinction coefficient,PbSe,Semiconductor nanocrystal,Size dependence,informative,size-exciton correlation}, mendeley-tags ={informative}, month = {jun}, pmid = 19435305, } @article{DeGeyter2012, author = {{De Geyter}, Bram and Geiregat, Pieter and Gao, Yunan and {Ten Cate}, Sybren and Houtepen, Arjan J. and Schins, Juleon M. and {Van Thourhout}, Dries and Siebbeles, Laurens D A and Hens, Zeger}, title = {{Broadband and picosecond intraband absorption in lead based colloidal quantum dots}}, journal = {ACS Nano}, number = 7, pages = {6067--6074}, year = 2012, doi = {10.1109/ICTON.2012.6254469}, abstract = {Using femtosecond transient absorption spectroscopy we demonstrate that lead chalcogenide nanocrystals show considerable, photoinduced absorption (PA) in a broad wavelength range just below the bandgap. The time-dependent decay of the PA signal correlates with the recovery of the band gap absorption, indicating that the same carriers are involved. Based on this, we assign this PA signal to intraband absorption, i.e., the excitation of photogenerated carriers from the bottom of the conduction band or the top of the valence band to higher energy levels in the conduction and valence band continuum. We confirm our experiments with tight-binding calculations. This broadband response in the commercially interesting near to mid-infrared range is very relevant for ultra high speed all optical signal processing. We benchmark the performance with bulk-Si and Si-nanocrystals.}, file = {::}, isbn = 9781467322270, issn = 21627339, keywords = {colloidal nanocrystals,free carrier absorption,intraband absorption,lead chalcogenide,optical signal processing,tight-binding,transient absorption spectroscopy}, pmid = 22686663, } @article{DelCoso2004, author = {del Coso, Ra{\'{u}}l and Solis, Javier}, title = {{Relation between nonlinear refractive index and third-order susceptibility in absorbing media}}, journal = {Journal of the Optical Society of America B}, volume = 21, number = 3, pages = 640, year = 2004, doi = {10.1364/JOSAB.21.000640}, url = {http://www.opticsinfobase.org/abstract.cfm?URI=JOSAB-21-3-640 https://www.osapublishing.org/abstract.cfm?URI=josab-21-3-640}, abstract = {Expressions relating complex third-order optical susceptibility ($\chi$(3)=$\chi$R(3)+i$\chi$I(3)) with nonlinear refractive index (n2) and nonlinear absorption coefficient ($\beta$) have been formulated that eliminate the commonly used approximation of a negligible linear absorption coefficient. The resulting equations do not show the conventional linear dependence of $\chi$R(3) with n2 and $\chi$I(3) with $\beta$. Nonlinear refraction and absorption result instead from the interplay between the real and imaginary parts of the first- and third-order susceptibilities of the material. This effect is illustrated in the case of a metal–dielectric nanocomposite for which n2 and $\beta$ values were experimentally obtained by Z-scan measurements and for which the use of the new formulas for $\chi$R(3) and $\chi$I(3) yield a large correction and a sign reversal for $\chi$I(3).}, file = {::}, issn = {0740-3224}, month = {mar}, pmid = 220057300022, } @article{Gdor2012, author = {Gdor, Itay and Sachs, Hanan and Roitblat, Avishy and Strasfeld, David B. and Bawendi, Moungi G. and Ruhman, Sanford}, title = {{Exploring exciton relaxation and multiexciton generation in PbSe nanocrystals using hyperspectral near-IR probing.}}, journal = {ACS nano}, volume = 6, number = 4, pages = {3269--77}, year = 2012, doi = {10.1021/nn300184n}, url = {http://www.ncbi.nlm.nih.gov/pubmed/22390473}, abstract = {Hyperspectral femtosecond transient absorption spectroscopy is employed to record exciton relaxation and recombination in colloidal lead selenide (PbSe) nanocrystals in unprecedented detail. Results obtained with different pump wavelengths and fluences are scrutinized with regard to three issues: (1) early subpicosecond spectral features due to "hot" excitons are analyzed in terms of suggested underlying mechanisms; (2) global kinetic analysis facilitates separation of the transient difference spectra into single, double, and triple exciton state contributions, from which individual band assignments can be tested; and (3) the transient spectra are screened for signatures of multiexciton generation (MEG) by comparing experiments with excitation pulses both below and well above the theoretical threshold for multiplication. For the latter, a recently devised ultrafast pump-probe spectroscopic approach is employed. Scaling sample concentrations and pump pulse intensities inversely with the extinction coefficient at each excitation wavelength overcomes ambiguities due to direct multiphoton excitation, uncertainties of absolute absorption cross sections, and low signal levels. As observed in a recent application of this method to InAs core/shell/shell nanodots, no sign of MEG was detected in this sample up to photon energy 3.7 times the band gap. Accordingly, numerous reports of efficient MEG in other samples of PbSe suggest that the efficiency of this process varies from sample to sample and depends on factors yet to be determined.}, file = {::}, isbn = {1936-086X (Electronic)$\backslash$r1936-0851 (Linking)}, issn = {1936-086X}, keywords = {SADS,carrier multiplication,ciency in nanocrystals has,exciton cooling,in accord,led,meg effi-,multiexciton generation,quantum dots,the apparent enhancement of,ultrafast spectroscopy}, mendeley-tags ={SADS}, month = {apr}, pmid = 22390473, } @article{Gdor2013a, author = {Gdor, Itay and Yang, Chunfan and Yanover, Diana and Sachs, Hanan and Lifshitz, Efrat and Ruhman, Sanford}, title = {{Novel Spectral Decay Dynamics of Hot Excitons in PbSe Nanocrystals: A Tunable Femtosecond Pump–Hyperspectral Probe Study}}, journal = {The Journal of Physical Chemistry C}, volume = 117, number = 49, pages = {26342--26350}, year = 2013, doi = {10.1021/jp409530z}, url = {http://pubs.acs.org/doi/abs/10.1021/jp409530z}, abstract = {Ultrafast exciton cooling in highly monodisperse PbSe nanocrystals is followed with tunable pump?hyperspectral near-IR probe spectroscopy. Unexpected kinetic and spectral correlations between induced bleach and absorption features are revealed, which are incompatible with standard models for excited nanocrystal absorption. Interband optical excitation immediately generates a sharp bleach feature near the 1Sh1Se transition which is unchanged during exciton thermalization, while pumping well above the band edge induces an intense absorption at frequencies just below the band edge which decays concurrently with a buildup of renewed absorbance at the 1Ph1Pe peak during exciton cooling. Transient spectra of hot single and double excitons are nearly indistinguishable, arguing against the controversial involvement of Auger cooling in the rapid dissipation of excess energy in excited PbSe QDs. Finally, quantitative signal analysis shows no signs of multiexciton generation up to photon energies four times the sample band gap. Ultrafast exciton cooling in highly monodisperse PbSe nanocrystals is followed with tunable pump?hyperspectral near-IR probe spectroscopy. Unexpected kinetic and spectral correlations between induced bleach and absorption features are revealed, which are incompatible with standard models for excited nanocrystal absorption. Interband optical excitation immediately generates a sharp bleach feature near the 1Sh1Se transition which is unchanged during exciton thermalization, while pumping well above the band edge induces an intense absorption at frequencies just below the band edge which decays concurrently with a buildup of renewed absorbance at the 1Ph1Pe peak during exciton cooling. Transient spectra of hot single and double excitons are nearly indistinguishable, arguing against the controversial involvement of Auger cooling in the rapid dissipation of excess energy in excited PbSe QDs. Finally, quantitative signal analysis shows no signs of multiexciton generation up to photon energies four times the sample band gap.}, file = {::}, isbn = 1557522790, issn = {1932-7447}, month = {dec}, } @article{Gdor2015, author = {Gdor, Itay and Shapiro, Arthur and Yang, Chunfan and Yanover, Diana and Lifshitz, Efrat and Ruhman, Sanford}, title = {{Three-pulse femtosecond spectroscopy of PbSe nanocrystals: 1S bleach nonlinearity and sub-band-edge excited-state absorption assignment}}, journal = {ACS Nano}, volume = 9, number = 2, pages = {2138--2147}, year = 2015, doi = {10.1021/nn5074868}, abstract = {Above band-edge photo-excitation of PbSe nanocrystals induces strong below band-gap absorption as well as a multi-phased buildup of bleaching in the 1Se1Sh transition. The amplitudes and kinetics of these features deviate from expectations based on bi-exciton shifts and state filling which are the mechanisms usually evoked to explain them. To clarify these discrepancies, the same transitions are investigated here by double-pump probe spectroscopy. Re-exciting in the below band-gap induced absorption characteristic of hot excitons is shown to produce additional excitons with high probability. In addition, pump-probe experiments on a sample saturated with single relaxed excitons proves that the resulting 1Se1Sh bleach is not linear with the number of excitons per nanocrystal. This finding holds for two samples differing significantly in size, demonstrating its generality. Analysis of the results suggest that below band edge induced absorption in hot exciton states is due to excited state absorption and not to shifted absorption of cold carriers, and that 1Se1Sh bleach signals are not an accurate counter of sample excitons when their distribution includes multi-exciton states.}, file = {::}, isbn = {1936-0851}, issn = {1936086X}, keywords = {exciton cooling,multiexciton generation,nanocrystals,quantum dots,ultrafast spectroscopy}, } @article{Gdor2015a, author = {Gdor, Itay and Yanover, Dianna and Yang, Chunfan and Shapiro, Arthur and Lifshitz, Efrat and Ruhman, Sanford}, title = {{Three Pulse Femtosecond Spectroscopy of PbSe Nano-Crystals ; 1S Bleach Nonlinearity and Sub Band-Edge Excited State Absorption Assignment Three Pulse Femtosecond Spectroscopy of PbSe nano-Crystals ; 1S Bleach Nonlinearity and Sub Band-edge Excited State A}}, journal = {ACS Nano}, pages = {2--5}, year = 2015, doi = {10.1021/nn5074868}, file = {::}, } @article{Geiregat2014, author = {Geiregat, Pieter and Houtepen, Arjan J. and Justo, Yolanda and Grozema, Ferdinand C. and {Van Thourhout}, Dries and Hens, Zeger}, title = {{Coulomb Shifts upon Exciton Addition to Photoexcited PbS Colloidal Quantum Dots}}, journal = {The Journal of Physical Chemistry C}, volume = 118, number = 38, pages = {22284--22290}, year = 2014, doi = {10.1021/jp505530k}, url = {http://pubs.acs.org/doi/abs/10.1021/jp505530k}, abstract = {Using ultrafast hyperspectral transient absorption (TA) spectroscopy, we determine the biexciton addition energies in PbS quantum dots (QDs) with different sizes when either a cold or a hot electron−hole pair is added to a QD already containing a cooled exciton. The observed dependence of this so-called biexciton addition energy on the QD diameter and the exciton energy can be rationalized by interpreting the addition energies as the result of an imbalance in the Coulomb interactions between the newly created carriers and the carriers already present in a QD. The obtained results are therefore relevant from both a fundamental and practical point of view. They provide experimental data on Coulomb interaction between charge carriers in confined semiconductors that can be compared with theoretical estimates. Moreover, understanding the way hot−cold biexciton addition energies influence the transient absorption spectrum adds a new element to the transient absorption toolbox for the optoelectronic properties of colloidal QDs. ■ INTRODUCTION Colloidal semiconductor nanocrystals or quantum dots (QDs) are an increasingly prominent class of low-dimensional nanomaterials that combine size-tunable electronic and optical properties with a suitability for solution-based processing. Starting from fundamental research and theoretical modeling on their unique physical properties, QDs are now applied in a variety of domains such as solar energy harvesting, photo-detection, and light-emitting diodes or displays. 1−5 These applications typically rely on the linear optical properties of QDs, i.e., light absorption by unexcited QDs and light emission by radiative recombination in excited QDs. On the other hand, various studies have shown that the spectral and time-dependent properties of excited QDs can strongly enhance the performance of QD-based devices in the above mention applications or enable QDs to be used in completely different applications. Quantum dots excited with photons having energies exceeding twice that of the QD bandgap transition can, for example, dissipate their excess energy by forming biexcitons in a process called multiple exciton generation (MEG) that can considerably enhance the short circuit current of single junction, QD-based solar cells. 2,6−8 Controlling the recombination rate of biexcitons by nonradiative Auger processes allowed for the formation of blinking-free QDs and facilitated the formation of QD-based lasers. 9,10 Moreover, it was proven that excited QDs exhibit a broadband and ultrafast photoinduced absorption related to intraband transitions of either the excited electron or hole, which could be used for optical modulation. 11,12}, file = {::;::}, issn = {1932-7447}, month = {sep}, } @article{Gesuele2012, author = {Gesuele, F and Sfeir, M Y and Murray, C B and Heinz, T F and Wong, C W}, title = {{Biexcitonic Effects in Excited Ultrafast Supercontinuum S{\aa}ectroscopy of Carrier Multiplication and Biexctionic Effects in Excited States of PbS Quantum Dots}}, journal = {Nano letters}, volume = 12, pages = 2658, year = 2012, file = {::}, keywords = {1,2 the strong spatial,based-materials for third-generation photovol-,carrier multiplication,confinement of electronic wave,here is great interest,in the properties of,multiple-exciton generation,qd,quantum dot,solar cells,taics,ultrafast spectroscopy}, } @article{Hogemann1996, author = {H{\"{o}}gemann, Claudia and Pauchard, Marc and Vauthey, Eric}, title = {{Picosecond transient grating spectroscopy: The nature of the diffracted spectrum}}, journal = {Review of Scientific Instruments}, volume = 67, number = 10, pages = {3449--3453}, year = 1996, doi = {10.1063/1.1147157}, url = {http://link.aip.org/link/RSINAK/v67/i10/p3449/s1{\&}Agg=doi http://aip.scitation.org/doi/10.1063/1.1147157}, file = {::}, issn = {0034-6748}, month = {oct}, } @article{Hutchings1992, author = {Hutchings, D C and Sheik-Bahae, M and Hagan, D J and {Van Stryland}, E W}, title = {{Kramers-Kronig relations in nonlinear optics}}, journal = {Optical and Quantum Electronics}, volume = 24, number = 1, pages = {1--30}, year = 1992, doi = {10.1007/BF01234275}, url = {http://dx.doi.org/10.1007/BF01234275{\%}5Cnhttp://www.springerlink.com/index/10.1007/BF01234275}, abstract = {We review dispersion relations, which relate the real part of the optical susceptibility (refraction) to the imaginary part (absorption). We derive and discuss these relations as applied to nonlinear optical systems. It is shown that in the nonlinear case, for self-action effects the correct form for such dispersion relations is nondegenerate, i.e. it is necessary to use multiple frequency arguments. Nonlinear dispersion relations have been shown to be very useful as they usually only require integration over a limited frequency range (corresponding to frequencies at which the absorption changes), unlike the conventional linear Kramers-Kr{\"{o}}nig relation which requires integration over all absorbing frequencies. Furthermore, calculation of refractive index changes using dispersion relations is easier than a direct calculation of the susceptibility, as transition rates (which give absorption coefficients) are, in general, far easier to calculate than the expectation value of the optical polarization. Both resonant (generation of some excitation that is long lived compared with an optical period) and nonresonant ‘instantaneous' optical nonlinearities are discussed, and it is shown that the nonlinear dispersion relation has a common form and can be understood in terms of the linear Kramers-Kr{\"{o}}nig relation applied to a new system consisting of the material plus some ‘perturbation'. We present several examples of the form of this external perturbation, which can be viewed as the pump in a pump-probe experiment. We discuss the two-level saturated atom model and bandfilling in semiconductors among others for the resonant case. For the nonresonant case some recent work is included where the electronic nonlinear refractive coefficient,n2, is determined from the nonlinear absorption processes of two-photon absorption, Raman transitions and the a.c. Stark effect. We also review how the dispersion relations can be extended to give alternative forms for frequency summation which, for example, allows the real and imaginary parts of?(2) to be related.}, file = {::;::}, isbn = {0306-8919}, issn = 03068919, } @article{Kang1997, author = {Kang, Inuk and Wise, Frank W.}, title = {{Electronic structure and optical properties of PbS and PbSe quantum dots}}, journal = {Journal of the Optical Society of America B}, volume = 14, number = 7, pages = 1632, year = 1997, doi = {10.1364/JOSAB.14.001632}, url = {http://www.opticsinfobase.org/abstract.cfm?URI=josab-14-7-1632}, file = {:C$\backslash$:/Users/Dan/AppData/Local/Mendeley Ltd./Mendeley Desktop/Downloaded/Kang, Wise - 1997 - Electronic structure and optical properties of PbS and PbSe quantum dots.pdf:pdf}, issn = {0740-3224}, month = {jul}, } @article{Karki2013, author = {Karki, Khadga J and Ma, Fei and Zheng, Kaibo and Zidek, Karel and Mousa, Abdelrazek and Abdellah, Mohamed and Messing, Maria E and Wallenberg, L Reine and Yartsev, Arkadi and Pullerits, T{\~{o}}nu}, title = {{Multiple exciton generation in nano-crystals revisited: consistent calculation of the yield based on pump-probe spectroscopy.}}, journal = {Scientific reports}, volume = 3, pages = 2287, year = 2013, doi = {10.1038/srep02287}, url = {http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=3724175{\&}tool=pmcentrez{\&}rendertype=abstract}, abstract = {Multiple exciton generation (MEG) is a process in which more than one exciton is generated upon the absorption of a high energy photon, typically higher than two times the band gap, in semiconductor nanocrystals. It can be observed experimentally using time resolved spectroscopy such as the transient absorption measurements. Quantification of the MEG yield is usually done by assuming that the bi-exciton signal is twice the signal from a single exciton. Herein we show that this assumption is not always justified and may lead to significant errors in the estimated MEG yields. We develop a methodology to determine proper scaling factors to the signals from the transient absorption experiments. Using the methodology we find modest MEG yields in lead chalcogenide nanocrystals including the nanorods.}, file = {::}, issn = {2045-2322}, month = {jan}, pmid = 23887181, } @article{Kohler2014, author = {Kohler, Daniel D. and Block, Stephen B. and Kain, Schuyler and Pakoulev, Andrei V. and Wright, John C.}, title = {{Ultrafast Dynamics within the 1S Exciton Band of Colloidal PbSe Quantum Dots Using Multiresonant Coherent Multidimensional Spectroscopy}}, journal = {The Journal of Physical Chemistry C}, volume = 118, number = 9, pages = {5020--5031}, year = 2014, doi = {10.1021/jp412058u}, url = {http://pubs.acs.org/doi/abs/10.1021/jp412058u}, file = {::}, issn = {1932-7447}, month = {mar}, } @article{Kohler2017, author = {Kohler, Daniel D and Thompson, Blaise J and Wright, John C}, title = {{Frequency-domain coherent multidimensional spectroscopy when dephasing rivals pulsewidth: Disentangling material and instrument response}}, journal = {The Journal of Chemical Physics}, volume = 147, number = 8, pages = 084202, year = 2017, doi = {10.1063/1.4986069}, url = {http://dx.doi.org/10.1063/1.4986069 http://aip.scitation.org/toc/jcp/147/8 http://aip.scitation.org/doi/10.1063/1.4986069}, abstract = {Ultrafast spectroscopy is often collected in the mixed frequency/time domain, where pulse durations are similar to system dephasing times. In these experiments, expectations derived from the familiar driven and impulsive limits are not valid. This work simulates the mixed-domain four-wave mixing response of a model system to develop expectations for this more complex field-matter interaction. We explore frequency and delay axes. We show that these line shapes are exquisitely sensitive to excitation pulse widths and delays. Near pulse overlap, the excitation pulses induce correlations that resemble signatures of dynamic inhomogeneity. We describe these line shapes using an intuitive picture that connects to familiar field-matter expressions. We develop strategies for distinguishing pulse-induced correlations from true system inhomogeneity. These simulations provide a founda-tion for interpretation of ultrafast experiments in the mixed domain.}, file = {::}, issn = {0021-9606}, month = {aug}, } @article{Kraatz2014, author = {Kraatz, Ingvar T and Booth, Matthew and Whitaker, Benjamin J and Nix, Michael G D and Critchley, Kevin}, title = {{Sub-Bandgap Emission and Intraband Defect-Related Excited-State Dynamics in Colloidal CuInS 2 /ZnS Quantum Dots Revealed by Femtosecond Pump − Dump − Probe Spectroscopy}}, year = {2014}, file = {::}, } @article{Lucarini2008, author = {Lucarini, Valerio}, title = {{Response theory for equilibrium and non-equilibrium statistical mechanics: Causality and generalized kramers-kronig relations}}, journal = {Journal of Statistical Physics}, volume = 131, number = 3, pages = {543--558}, year = 2008, doi = {10.1007/s10955-008-9498-y}, abstract = {We consider the general response theory proposed by Ruelle for describing the impact of small perturbations to the non-equilibrium steady states resulting from Axiom A dynamical systems. We show that the causality of the response functions allows for writing a set of Kramers-Kronig relations for the corresponding susceptibilities at all orders of nonlinearity. Nonetheless, only a special class of observable susceptibilities obey Kramers-Kronig relations. Specific results are provided for arbitrary order harmonic response, which allows for a very comprehensive Kramers-Kronig analysis and the establishment of sum rules connecting the asymptotic behavior of the susceptibility to the short-time response of the system. These results generalize previous findings on optical Hamiltonian systems and simple mechanical models, and shed light on the general impact of considering the principle of causality for testing self-consistency: the described dispersion relations constitute unavoidable benchmarks for any experimental and model generated dataset. In order to connect the response theory for equilibrium and non equilibrium systems, we rewrite the classical results by Kubo so that response functions formally identical to those proposed by Ruelle, apart from the measure involved in the phase space integration, are obtained. We briefly discuss how these results, taking into account the chaotic hypothesis, might be relevant for climate research. In particular, whereas the fluctuation-dissipation theorem does not work for non-equilibrium systems, because of the non-equivalence between internal and external fluctuations, Kramers-Kronig relations might be more robust tools for the definition of a self-consistent theory of climate change.}, archivePrefix ={arXiv}, arxivId = {0710.0958}, eprint = {0710.0958}, file = {::}, issn = 00224715, keywords = {Axiom A dynamical systems,Chaotic hypothesis,Climate,Harmonic generation,Kramers-Kronig relations,Kubo response theory,Non-equilibrium steady states,Ruelle response theory,SRB measure}, } @article{Moreels2006, author = {Moreels, I. and Hens, Z. and Kockaert, P. and Loicq, J. and {Van Thourhout}, D.}, title = {{Spectroscopy of the nonlinear refractive index of colloidal PbSe nanocrystals}}, journal = {Applied Physics Letters}, volume = 89, number = 19, pages = {0--4}, year = 2006, doi = {10.1063/1.2385658}, abstract = {A spectroscopic study of the optical nonlinearity of PbSe colloidal solutions was performed with the Z-scan technique at wavelength intervals of 1200-1350 and 1540-1750 nm. While nonlinear absorption remains below the detection threshold, the third order nonlinear refractive index n(2) shows clear resonances, somewhat blueshifted relative to the exciton transitions in the absorbance spectrum. The occurrence of thermal effects is ruled out by time-resolved measurements. At 1.55 mu m, measured (resonant) n(2) values exceed typical bulk semiconductor values by two orders of magnitude. At high optical intensity, the refractive index change saturates, indicating that statefilling lies at the origin of the observed effect.}, file = {::}, isbn = {0003-6951}, issn = 00036951, } @article{Moreels2007, author = {Moreels, Iwan and Lambert, Karel and {De Muynck}, David and Vanhaecke, Frank and Poelman, Dirk and Martins, Jos{\'{e}} C. and Allan, Guy and Hens, Zeger}, title = {{Composition and Size-Dependent Extinction Coefficient of Colloidal PbSe Quantum Dots}}, journal = {Chemistry of Materials}, volume = 19, number = 25, pages = {6101--6106}, year = 2007, doi = {10.1021/cm071410q}, url = {http://pubs.acs.org/doi/abs/10.1021/cm071410q}, file = {::}, issn = {0897-4756}, keywords = {reference,size-exciton correlation}, mendeley-tags ={reference}, month = {dec}, } @article{Moreels2008, author = {Moreels, Iwan and Hens, Zeger}, title = {{On the interpretation of colloidal quantum-dot absorption spectra.}}, journal = {Small (Weinheim an der Bergstrasse, Germany)}, volume = 4, number = 11, pages = {1866--8; author reply 1869--70}, year = 2008, doi = {10.1002/smll.200800068}, url = {http://www.ncbi.nlm.nih.gov/pubmed/18855972}, file = {::}, issn = {1613-6829}, keywords = {Absorption,Colloids,Colloids: chemistry,Quantum Dots,Spectrum Analysis,Spectrum Analysis: methods}, month = {nov}, pmid = 18855972, } @article{Moreels2009, author = {Moreels, Iwan and Lambert, Karel and Muynck, David De and Vanhaecke, Frank and Poelman, Dirk and Martins, Jos{\'{e}} C and Allan, Guy and Hens, Zeger}, title = {{Size-Dependent Optical Properties of Colloidal {\{}PbS{\}} Quantum Dots}}, journal = {ACS Nano}, volume = 3, number = 10, pages = {3023--3030}, year = 2009, doi = {10.1021/nn900863a}, abstract = {We quantitatively investigate the size-dependent optical properties of colloidal {\{}PbS{\}} nanocrystals or quantum dots (Qdots), by combining the Qdot absorbance spectra with detailed elemental analysis of the Qdot suspensions. At high energies, the molar extinction coefficient ?? increases with the Qdot volume d3 and agrees with theoretical calculations using the Maxwell???Garnett effective medium theory and bulk values for the Qdot dielectric function. This demonstrates that quantum confinement has no influence on ?? in this spectral range, and it provides an accurate method to calculate the Qdot concentration. Around the band gap, ?? only increases with d1.3, and values are comparable to the ?? of {\{}PbSe{\}} Qdots. The data are related to the oscillator strength fif of the band gap transition and results agree well with theoretical tight-binding calculations, predicting a linear dependence of fif on d. For both {\{}PbS{\}} and {\{}PbSe{\}} Qdots, the exciton lifetime ?? is calculated from fif. We find values ranging between 1 and 3 ??s, in agreement with experimental literature data from time-resolved luminescence spectroscopy. Our results provide a thorough general framework to calculate and understand the optical properties of suspended colloidal quantum dots. Most importantly, it highlights the significance of the local field factor in these systems.}, file = {::}, issn = {1936-0851}, keywords = {exciton lifetime,extinction coefficient,lead chalcogenide,molar,oscillator strength,pbse,semiconductor nanocrystals}, } @article{Nootz2011, author = {Nootz, Gero and Padilha, Lazaro A. and Levina, Larissa and Sukhovatkin, Vlad and Webster, Scott and Brzozowski, Lukasz and Sargent, Edward H. and Hagan, David J. and {Van Stryland}, Eric W.}, title = {{Size dependence of carrier dynamics and carrier multiplication in PbS quantum dots}}, journal = {Physical Review B - Condensed Matter and Materials Physics}, volume = 83, number = 15, pages = {1--7}, year = 2011, doi = {10.1103/PhysRevB.83.155302}, abstract = {The time dynamics of the photoexcited carriers and carrier-multiplication efficiencies in PbS quantum dots (QDs) are investigated. In particular, we report on the carrier dynamics, including carrier multiplication, as a function of QD size and compare them to the bulk value. We show that the intraband 1P -{\textgreater} 1S decay becomes faster for smaller QDs, in agreement with the absence of a phonon bottleneck. Furthermore, as the size of the QDs decreases, the energy threshold for carrier multiplication shifts from the bulk value to higher energies. However, the energy threshold shift is smaller than the band-gap shift and, therefore, for the smallest QDs, the threshold approaches 2.35 E(g), which is close to the theoretical energy conservation limit of twice the band gap. We also show that the carrier-multiplication energy efficiency increases with decreasing QD size. By comparing to theoretical models, our results suggest that impact ionization is sufficient to explain carrier multiplication in QDs.}, file = {::}, isbn = {1098-0121}, issn = 10980121, } @article{Okumura1999, author = {Okumura, Ko and Tokmakoff, Andrei and Tanimura, Yoshitaka}, title = {{Two-dimensional line-shape analysis of photon-echo signal}}, journal = {Chemical Physics Letters}, volume = 314, number = {5-6}, pages = {488--495}, year = 1999, doi = {10.1016/S0009-2614(99)01173-2}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0009261499011732}, abstract = {We analyze the two-dimensional (2D) line shape obtained by 2D Fourier transforming the time-domain response of a photon-echo signal as a function of the two coherence periods, t(1) and t(3). The line shape obtained for a two-level system with homogeneous and inhomogeneous broadening is shown to be sensitive to the magnitude of both of these line-broadening mechanisms. It is shown that the ellipticity of the 2D line shape can be related to the ratio of homogeneous to inhomogeneous broadening. (C) 1999 Elsevier Science B.V. All rights reserved.}, file = {:C$\backslash$:/Users/Dan/AppData/Local/Mendeley Ltd./Mendeley Desktop/Downloaded/Okumura, Tokmakoff, Tanimura - 1999 - Two-dimensional line-shape analysis of photon-echo signal.pdf:pdf}, isbn = {0009-2614}, issn = 00092614, keywords = {3rd-order,dynamics,glasses,phase,probes,spectroscopy}, month = {dec}, } @article{Olivero1977, author = {Olivero, J.J. and Longbothum, R.L.}, title = {{Empirical fits to the voigt line width: A brief review}}, journal = {J. Quant. Spectrosc. Radiat. Transfer}, volume = 17, pages = {233--236}, year = 1977, file = {::}, } @article{Omari2012, author = {Omari, Abdoulghafar and Moreels, Iwan and Masia, Francesco and Langbein, Wolfgang and Borri, Paola and {Van Thourhout}, Dries and Kockaert, Pascal and Hens, Zeger}, title = {{Role of interband and photoinduced absorption in the nonlinear refraction and absorption of resonantly excited PbS quantum dots around 1550 nm}}, journal = {Physical Review B}, volume = 85, number = 11, pages = 115318, year = 2012, doi = {10.1103/PhysRevB.85.115318}, url = {http://link.aps.org/doi/10.1103/PhysRevB.85.115318}, file = {::}, issn = {1098-0121}, month = {mar}, } @article{Pang1991, author = {Pang, Yang and Samoc, Marek and Prasad, Paras N.}, title = {{Third‐order nonlinearity and two‐photon‐induced molecular dynamics: Femtosecond time‐resolved transient absorption, Kerr gate, and degenerate four‐wave mixing studies in poly ( p ‐phenylene vinylene)/sol‐gel silica film}}, journal = {The Journal of Chemical Physics}, volume = 94, number = 8, pages = {5282--5290}, year = 1991, doi = {10.1063/1.460512}, url = {http://scitation.aip.org/content/aip/journal/jcp/94/8/10.1063/1.460512 http://aip.scitation.org/doi/10.1063/1.460512}, abstract = {Femtosecond response and relaxation of the third-order optical nonlinearity in a newly developed poly (p-phenylene vinylene)/sol-gel silica composite are investigated by time- resolved forward wave degenerate four-wave mixing, Kerr gate, and transient absorption techniques using 60 fs pulses at 620 nm. Using a theoretical description of two- and four-wave mixing in optically nonlinear media, it is shown that the results obtained from simultaneous use of these techniques yield valuable information on the real and imaginary components of the third-order susceptibility. In the composite material investigated here, the imaginary component is derived from the presence of a two-photon resonance at the wavelength of 620 nm used for the present study. This two-photon resonance is observed as transient absorption of the probe beam induced by the presence of a strong pump beam. It also provides fifth-order nonlinear response both in transient absorption and in degenerate four-wave mixing. The fifth- order contributions are derived from the two-photon generated excited species which can absorb at the measurement wavelength and therefore modify both the absorption coefficient and the refractive index of the medium.}, file = {::}, issn = {0021-9606}, month = {apr}, } @article{Peterson2007, author = {Peterson, JJ and Huang, Libai and Delerue, C. and Allan, Guy}, title = {{Uncovering forbidden optical transitions in PbSe nanocrystals}}, journal = {nano Letters}, year = 2007, url = {http://pubs.acs.org/doi/abs/10.1021/nl072487g}, file = {:C$\backslash$:/Users/Dan/AppData/Local/Mendeley Ltd./Mendeley Desktop/Downloaded/Peterson et al. - 2007 - Uncovering forbidden optical transitions in PbSe nanocrystals.pdf:pdf}, keywords = {1P exciton,2 photon absorption,new,relevant}, mendeley-tags ={new,relevant}, } @article{Price2015, author = {Price, Michael B. and Butkus, Justinas and Jellicoe, Tom C. and Sadhanala, Aditya and Briane, Anouk and Halpert, Jonathan E. and Broch, Katharina and Hodgkiss, Justin M. and Friend, Richard H. and Deschler, Felix}, title = {{Hot-carrier cooling and photoinduced refractive index changes in organic–inorganic lead halide perovskites}}, journal = {Nature Communications}, volume = 6, number = {May}, pages = 8420, year = 2015, doi = {10.1038/ncomms9420}, url = {http://dx.doi.org/10.1038/ncomms9420 http://www.nature.com/doifinder/10.1038/ncomms9420}, archivePrefix ={arXiv}, arxivId = {arXiv:1504.07508}, eprint = {arXiv:1504.07508}, file = {::}, issn = {2041-1723}, publisher = {Nature Publishing Group}, } @article{Schaller2003, author = {Schaller, Richard D and Petruska, M. a. and Klimov, Victor I.}, title = {{Tunable Near-Infrared Optical Gain and Amplified Spontaneous Emission Using PbSe Nanocrystals}}, journal = {The Journal of Physical Chemistry B}, volume = 107, number = 50, pages = {13765--13768}, year = 2003, doi = {10.1021/jp0311660}, url = {http://pubs.acs.org/doi/abs/10.1021/jp0311660}, file = {::;::}, issn = {1520-6106}, month = {dec}, } @article{Schins2009, author = {Schins, Juleon and Trinh, M. and Houtepen, Arjan and Siebbeles, Laurens}, title = {{Probing formally forbidden optical transitions in PbSe nanocrystals by time- and energy-resolved transient absorption spectroscopy}}, journal = {Physical Review B}, volume = 80, number = 3, pages = 035323, year = 2009, doi = {10.1103/PhysRevB.80.035323}, url = {http://link.aps.org/doi/10.1103/PhysRevB.80.035323}, file = {::}, issn = {1098-0121}, month = {jul}, } @article{Svirko1999, author = {{P. Svirko}, Yuri and Shirane, Masayuki and Suzuura, Hidekatsu and Kuwata-Gonokami, Makoto}, title = {{Four-Wave Mixing Theory at the Excitonic Resonance: Weakly Interacting Boson Model}}, journal = {Journal of the Physical Society of Japan}, volume = 68, number = 2, pages = {674--682}, year = 1999, doi = {10.1143/JPSJ.68.674}, url = {http://journals.jps.jp/doi/10.1143/JPSJ.68.674}, file = {::}, issn = {0031-9015}, keywords = {Exciton,Four-particle correlation,Four-wave mixing,Normal mode splitting,Semiconductor microcavity}, month = {feb}, } @article{Trinh2008, author = {Trinh, M Tuan and Houtepen, Arjan J and Schins, Juleon M and Piris, Jorge and Siebbeles, Laurens D a}, title = {{Nature of the second optical transition in PbSe nanocrystals.}}, journal = {Nano letters}, volume = 8, number = 7, pages = {2112--7}, year = 2008, doi = {10.1021/nl8010963}, url = {http://www.ncbi.nlm.nih.gov/pubmed/18510369}, abstract = {The second peak in the optical absorption spectrum of PbSe nanocrystals is arguably the most discussed optical transition in semiconductor nanocrystals. Ten years of scientific debate have produced many theoretical and experimental claims for the assignment of this feature as the 1P e1P h as well as the 1S h,e1P e,h transitions. We studied the nature of this absorption feature by pump-probe spectroscopy, exactly controlling the occupation of the states involved, and present conclusive evidence that the optical transition involves neither 1S e nor 1S h states. This suggests that it is the 1P h1P e transition that gives rise to the second peak in the absorption spectrum of PbSe nanocrystals.}, file = {::}, issn = {1530-6984}, month = {jul}, pmid = 18510369, } @article{Trinh2013, author = {Trinh, M. Tuan and Sfeir, Matthew Y. and Choi, Joshua J. and Owen, Jonathan S. and Zhu, Xiaoyang}, title = {{A Hot Electron–Hole Pair Breaks the Symmetry of a Semiconductor Quantum Dot}}, journal = {Nano Letters}, volume = 13, number = 12, pages = {6091--6097}, year = 2013, doi = {10.1021/nl403368y}, url = {http://pubs.acs.org/doi/abs/10.1021/nl403368y}, file = {::}, issn = {1530-6984}, keywords = {google the phrase,hot carriers,nanocrystals or,near the bandgap is,now well-,one,ptical excitation of semiconductor,qds,quantum dots,selection rules,stark effect,symmetry breaking,transient absorption,understood}, month = {dec}, } @article{Wehrenberg2002, author = {Wehrenberg, Brian L. and Wang, Congjun and Guyot-Sionnest, Philippe}, title = {{Interband and Intraband Optical Studies of PbSe Colloidal Quantum Dots}}, journal = {The Journal of Physical Chemistry B}, volume = 106, number = 41, pages = {10634--10640}, year = 2002, doi = {10.1021/jp021187e}, url = {http://pubs.acs.org/doi/abs/10.1021/jp021187e}, file = {::}, issn = {1520-6106}, month = {oct}, } @article{Wise2000, author = {Wise, Frank W.}, title = {{Lead salt quantum dots: the limit of strong quantum confinement.}}, journal = {Accounts of chemical research}, volume = 33, number = 11, pages = {773--80}, year = 2000, url = {http://www.ncbi.nlm.nih.gov/pubmed/11087314}, abstract = {Nanocrystals or quantum dots of the IV-VI semiconductors PbS, PbSe, and PbTe provide unique properties for investigating the effects of strong confinement on electrons and phonons. The degree of confinement of charge carriers can be many times stronger than in most II-VI and III-V semiconductors, and lead salt nanostructures may be the only materials in which the electronic energies are determined primarily by quantum confinement. This Account briefly reviews recent research on lead salt quantum dots.}, file = {:C$\backslash$:/Users/Dan/AppData/Local/Mendeley Ltd./Mendeley Desktop/Downloaded/Wise - 2000 - Lead salt quantum dots the limit of strong quantum confinement.pdf:pdf}, issn = {0001-4842}, keywords = {Crystallization,Electrochemistry,Lead,Lead: chemistry,Semiconductors,Temperature}, month = {nov}, pmid = 11087314, } @article{Yang2015, author = {Yang, Ye and Yan, Yong and Yang, Mengjin and Choi, Sukgeun and Zhu, Kai and Luther, Joseph M and Beard, Matthew C}, title = {{Low surface recombination velocity in}}, journal = {Nature Communications}, volume = 6, pages = {1--6}, year = 2015, doi = {10.1038/ncomms8961}, url = {http://dx.doi.org/10.1038/ncomms8961}, file = {::}, publisher = {Nature Publishing Group}, } @article{Yang2017, author = {Yang, Ye and Yang, Mengjin and Moore, David?T. and Yan, Yong and Miller, Elisa?M. and Zhu, Kai and Beard, Matthew?C.}, title = {{Top and bottom surfaces limit carrier lifetime in lead iodide perovskite films}}, journal = {Nature Energy}, volume = 2, number = 2, pages = 16207, year = 2017, doi = {10.1038/nenergy.2016.207}, url = {http://www.nature.com/articles/nenergy2016207}, abstract = {Carrier recombination at defects is detrimental to the performance of solar energy conversion systems, including solar cells and photoelectrochemical devices. Point defects are localized within the bulk crystal while extended defects occur at surfaces and grain boundaries. If not properly managed, surfaces can be a large source of carrier recombination. Separating surface carrier dynamics from bulk and/or grain-boundary recombination in thin films is challenging. Here, we employ transient reflection spectroscopy to measure the surface carrier dynamics in methylammonium lead iodide perovskite polycrystalline films. We find that surface recombination limits the total carrier lifetime in perovskite polycrystalline thin films, meaning that recombination inside grains and/or at grain boundaries is less important than top and bottom surface recombination. The surface recombination velocity in polycrystalline films is nearly an order of magnitude smaller than that in single crystals, possibly due to unintended surface passivation of the films during synthesis.}, file = {::}, issn = {2058-7546}, month = {jan}, } @article{Yurs2011, author = {Yurs, Lena A and Block, Stephen B and Pakoulev, Andrei V. and Selinsky, Rachel S. and Jin, Song and Wright, John}, title = {{Multiresonant Coherent Multidimensional Electronic Spectroscopy of Colloidal PbSe Quantum Dots}}, journal = {The Journal of Physical Chemistry C}, volume = 115, number = 46, pages = {22833--22844}, year = 2011, doi = {10.1021/jp207273x}, url = {http://pubs.acs.org/doi/abs/10.1021/jp207273x}, file = {::}, issn = {1932-7447}, month = {nov}, } @article{Yurs2012, author = {Yurs, Lena A and Block, Stephen B and Pakoulev, Andrei V. and Selinsky, Rachel S. and Jin, Song and Wright, John}, title = {{Spectral Isolation and Measurement of Surface-Trapped State Multidimensional Nonlinear Susceptibility in Colloidal Quantum Dots}}, journal = {The Journal of Physical Chemistry C}, volume = 116, number = 9, pages = {5546--5553}, year = 2012, doi = {10.1021/jp3014139}, url = {http://pubs.acs.org/doi/abs/10.1021/jp3014139}, file = {::}, issn = {1932-7447}, month = {mar}, }