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Ripberger HH, Schnitzenbaumer KJ, Nguyen LK, Ladd DM, Levine KR, Dayton DG, Toney MF, Cossairt BM. Navigating the Potential Energy Surface of CdSe Magic-Sized Clusters: Synthesis and Interconversion of Atomically Precise Nanocrystal Polymorphs. J Am Chem Soc 2023; 145:27480-27492. [PMID: 38061033 DOI: 10.1021/jacs.3c08897] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2023]
Abstract
Magic-sized clusters (MSCs) are kinetically stable, atomically precise intermediates along the quantum dot (QD) reaction potential energy surface. Literature precedent establishes two classes of cadmium selenide MSCs with QD-like inorganic cores: one class is proposed to be cation-rich with a zincblende crystal structure, while the other is proposed to be stoichiometric with a "wurtzite-like" core. However, the wide range of synthetic protocols used to access MSCs has made direct comparisons of their structure and surface chemistry difficult. Furthermore, the physical and chemical relationships between MSC polymorphs are yet to be established. Here, we demonstrate that both cation-rich and stoichiometric CdSe MSCs can be synthesized from identical reagents and can be interconverted through the addition of either excess cadmium or selenium precursor. The structural and compositional differences between these two polymorphs are contrasted using a combination of 1H NMR spectroscopy, X-ray diffraction (XRD), pair distribution function (PDF) analysis, inductively coupled plasma optical emission spectroscopy, and UV-vis transient absorption spectroscopy. The subsequent polymorph interconversion reactions are monitored by UV-vis absorption spectroscopy, with evidence for an altered cluster atomic structure observed by powder XRD and PDF analysis. This work helps to simplify the complex picture of the CdSe nanocrystal landscape and provides a method to explore structure-property relationships in colloidal semiconductors through atomically precise synthesis.
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Affiliation(s)
- Hunter H Ripberger
- Department of Chemistry, University of Washington, Seattle, Washington 98195-1700, United States
| | - Kyle J Schnitzenbaumer
- Division of Natural Sciences and Mathematics, Transylvania University, Lexington, Kentucky 40508-1797, United States
| | - Lily K Nguyen
- Department of Chemistry, University of Washington, Seattle, Washington 98195-1700, United States
| | - Dylan M Ladd
- Materials Science and Engineering Program, University of Colorado, Boulder, Colorado 80309, United States
| | - Kelsey R Levine
- Materials Science and Engineering Program, University of Colorado, Boulder, Colorado 80309, United States
| | - Damara G Dayton
- Materials Science and Engineering Program, University of Colorado, Boulder, Colorado 80309, United States
| | - Michael F Toney
- Materials Science and Engineering Program, University of Colorado, Boulder, Colorado 80309, United States
- Department of Chemical and Biological Engineering, Renewable and Sustainable Energy Institute, University of Colorado, Boulder, Colorado 80309, United States
| | - Brandi M Cossairt
- Department of Chemistry, University of Washington, Seattle, Washington 98195-1700, United States
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2
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Thrupthika T, Nataraj D, Ramya S, Sangeetha A, Thangadurai TD. Induced UV photon sensing properties in narrow bandgap CdTe quantum dots through controlling hot electron dynamics. Phys Chem Chem Phys 2023; 25:25331-25343. [PMID: 37702661 DOI: 10.1039/d3cp02424e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/14/2023]
Abstract
Mn-doped CdTe (Mn-CdTe) quantum dot (QD) as well as quantum dot solid (QD solid) nanostructures are formed and the established structures are confirmed through HR-TEM analysis. The dynamics of charge carriers in both doped & undoped QD and QD solid structures were investigated by transient absorption (TA) spectroscopy. A slow band edge bleach recovery is obtained for Mn-doped CdTe QD and CdTe QD solid systems at room temperature. Additionally, a blue shifted broad bleach behaviour is identified for the Mn-CdTe QD solid system, which is attributed to hot exciton formation in the solid upon photoexcitation with a higher photon energy than the band gap energy (hν > Eg). This noteworthy process of generation of hot excitons and slow charge recombination occurs by means of a synergetic action of the Mn dopant in the host CdTe QD solid system as well as the extended electronic wave function between the coupled QD solid. Apart from the Mn-assisted delayed relaxation of hot electrons in the QD solid, a suppression in dark current as well as a high ION/IOFF ratio of 3203.12 at 1 V is observed in the Mn-CdTe QD-solid based photosensitized device in the visible region. Furthermore, we were able to improve the UV photon harvesting property in a narrow band gap Mn-CdTe QD solid through reducing the higher excited carrier's energy losses.
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Affiliation(s)
- Thankappan Thrupthika
- Quantum Materials & Devices Laboratory, Department of Physics, Bharathiar University, Coimbatore, Tamil Nadu 641 046, India.
| | - Devaraj Nataraj
- Quantum Materials & Devices Laboratory, Department of Physics, Bharathiar University, Coimbatore, Tamil Nadu 641 046, India.
- UGC-CPEPA Centre for Advanced Studies in Physics for the Development of Solar Energy Materials and Devices, Department of Physics, Bharathiar University, Coimbatore, Tamil Nadu, 641 046, India
| | - Subramaniam Ramya
- Quantum Materials & Devices Laboratory, Department of Physics, Bharathiar University, Coimbatore, Tamil Nadu 641 046, India.
| | - Arumugam Sangeetha
- Quantum Materials & Devices Laboratory, Department of Physics, Bharathiar University, Coimbatore, Tamil Nadu 641 046, India.
| | - T Daniel Thangadurai
- KPR Institute of Engineering and Technology, Coimbatore, Tamil Nadu, 641 407, India.
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3
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Das S, Rana G, Ali F, Datta A. Single particle level dynamics of photoactivation and suppression of Auger recombination in aqueous Cu-doped CdS quantum dots. NANOSCALE 2023; 15:4469-4476. [PMID: 36752332 DOI: 10.1039/d2nr06688b] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Cu-doped CdS quantum dots (QDs) have been synthesized in water using 3-mercaptopropionic acid (3-MPA) as the capping agent. They exhibit intense photoluminescence and excellent color tunability, unlike most of the QDs synthesized/dispersed in water so far. Complete characterization of these aqueous doped CdS QDs has been performed for the first time, along with a single particle level elucidation of their exciton dynamics using fluorescence correlation spectroscopy. Photoactivation via dim/dark to bright particle conversion is observed at higher excitation powers. Dispersive blinking kinetics in undoped QDs reflects the involvement of a broad distribution of trap states. A lesser extent of dispersity is observed for doped QDs, in which hole-capture by Cu-defect states predominates. Excitation fluence dependence of the blinking rate highlights the role of Auger recombination in undoped QDs, which is suppressed significantly upon doping, due to disruption of the electron-hole correlation.
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Affiliation(s)
- Sharmistha Das
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
| | - Gourab Rana
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
| | - Fariyad Ali
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
| | - Anindya Datta
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
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4
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Palato S, Seiler H, Baker H, Sonnichsen C, Brosseau P, Kambhampati P. Investigating the electronic structure of confined multiexcitons with nonlinear spectroscopies. J Chem Phys 2020; 152:104710. [DOI: 10.1063/1.5142180] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Affiliation(s)
- S. Palato
- Department of Chemistry, McGill University, 801 Sherbrooke Street W, Montréal, Québec H3A 0B8, Canada
| | - H. Seiler
- Department of Chemistry, McGill University, 801 Sherbrooke Street W, Montréal, Québec H3A 0B8, Canada
| | - H. Baker
- Department of Chemistry, McGill University, 801 Sherbrooke Street W, Montréal, Québec H3A 0B8, Canada
| | - C. Sonnichsen
- Department of Chemistry, McGill University, 801 Sherbrooke Street W, Montréal, Québec H3A 0B8, Canada
| | - P. Brosseau
- Department of Chemistry, McGill University, 801 Sherbrooke Street W, Montréal, Québec H3A 0B8, Canada
| | - P. Kambhampati
- Department of Chemistry, McGill University, 801 Sherbrooke Street W, Montréal, Québec H3A 0B8, Canada
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5
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Shrivas K, Ghosale A, Kant T, Bajpai PK, Shankar R. The direct-writing of low cost paper based flexible electrodes and touch pad devices using silver nano-ink and ZnO nanoparticles. RSC Adv 2019; 9:17868-17876. [PMID: 35520587 PMCID: PMC9064668 DOI: 10.1039/c9ra02599e] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2019] [Accepted: 05/20/2019] [Indexed: 12/19/2022] Open
Abstract
We report a novel and simple approach for the synthesis of silver nanoparticles capped with inositol (Ag NPs/Ino) by the reduction of silver salt with ascorbic acid under basic conditions. UV-vis, TEM, FTIR and TGA techniques were used to characterize the Ag NPs/Ino to determine the size, shape and surface modification of the NPs. Stable silver nano-ink was prepared in aqueous solution containing 1% PVP (stabilizer) and glycerol (cosolvent) and was used for the direct-writing of a paper electrode with a roller ball-point pen for electrochemical applications. The solvent, stabilizing agents, concentration of NPs (10%), paper substrate, sintering temperature (40 °C) and sintering time (15 min) were optimized to obtain a uniform coating of Ag NPs on the paper substrate. Further, the synthesis and fabrication of ZnO NPs on a paper substrate was put forward to design a touch pad device based on the piezoelectric effect. The preparation of paper based devices suggests a direction for the development of a simple, low cost and compatible approach for the direct-writing of paper based flexible electrodes and electronics for future applications.
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Affiliation(s)
- Kamlesh Shrivas
- Department of Chemistry, Guru Ghasidas Vishwavidyalaya, Koni Bilaspur CG India .,School of Studies in Chemistry, Pt. Ravishankar Shukla University Raipur 492010 CG India
| | - Archana Ghosale
- Department of Chemistry, Guru Ghasidas Vishwavidyalaya, Koni Bilaspur CG India
| | - Tushar Kant
- School of Studies in Chemistry, Pt. Ravishankar Shukla University Raipur 492010 CG India
| | - P K Bajpai
- Department of Pure and Applied Physics, Guru Ghasidas Vishwavidyalaya, Koni Bilaspur CG India
| | - Ravi Shankar
- Nanoscience and Nanoengineering Program, South Dakota School of Mines and Technology Rapid City South Dakota 57701 USA
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Gostev FE, Shelaev IV, Aibush AV, Kostrov AN, Titov AA, Kochev SY, Kabachii YA, Denisov NN, Nadtochenko VA. Coherent Acoustic Phonon Activation by Fast Electron Transfer in the Exciton Redox-Quenching Reaction with Methyl Viologen in Cadmium Selenide. HIGH ENERGY CHEMISTRY 2019. [DOI: 10.1134/s001814391806005x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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7
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Cherepanov DA, Gostev FE, Shelaev IV, Denisov NN, Nadtochenko VA. Monitoring the electric field in CdSe quantum dots under ultrafast interfacial electron transfer via coherent phonon dynamics. NANOSCALE 2018; 10:22409-22419. [PMID: 30475371 DOI: 10.1039/c8nr07644h] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Coherent phonon dynamics in CdSe quantum dots (QD) under an ultrafast electron transfer (ET) reaction of the (1Se-1S3/2) exciton quenched by methyl viologen (MV2+) adsorbed onto the QD surface was studied by ultrafast pump-probe spectroscopy. Frequency and amplitude modulations (FM, AM) of the transient absorption ΔA(ωprobe,t) in the pure CdSe and coupled CdSe/MV2+ QDs were identified in the bleach band dynamics of the red-edge exciton. The fast Fourier transform (FFT) and continuous wavelet transform analysis of the FM and AM oscillations revealed peaks at 0.51-0.58 THz (17-19 cm-1) and 6.06-6.27 THz (202-209 cm-1) attributed to the longitudinal acoustic (LA) and longitudinal optical (LO) phonons, respectively. The electron transfer to MV2+ proceeded non-exponentially with effective time constants of 164 fs (∼30%) and 540 fs (∼70%). The quantum yield of MV˙+ radical formation was 40 ± 5%. It implies a fast route for the electron-hole pair [h+…MV˙+] recombination that can be rationalized in accordance with the adiabatic ET mechanism at the semiconductor surface. In the coupled CdSe/MV2+ QDs, the amplitude of the FM oscillations rose considerably with time despite the natural attenuation of the phonon amplitude due to decoherence processes. A kinetic model explaining the increase of FM oscillations is proposed. The surprising growth of FM oscillations is elucidated by the kinetic model taking into account the relatively slow damping of LO phonon oscillations (∼1.5 ps), the ultrafast ET to MV2+, and the quantum yield of charge separation [h+…MV˙+] (∼40%). The fast formation of the charge-separated pair [h+…MV˙+] suggests the appearance of an electric field F with a strength of ∼3 × 106 V cm-1. The MV2+ reduction substantially increased the magnitude of LA phonon oscillations. Since the ET time is shorter than the period of LA phonon oscillations (∼1.8 ps), the MV2+ reduction substantially increased the magnitude of LA phonon oscillations due to the inverse piezoelectric effect. The CdSe nanocrystals exposed to the electric field F exhibit the quantum-confined Stark and Franz-Keldysh electro-absorption effects. The proposed kinetic model gives consideration to the dynamic Stark shift of the red-edge exciton and to the increased amplitude of LO phonon oscillations in the bleach band dynamics.
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Affiliation(s)
- Dmitry A Cherepanov
- N.Semenov Institute of Chemical Physics Russian Academy of Sciences, Kosigin str.4, Moscow, 119991, Russia.
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8
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Schnitzenbaumer KJ, Dukovic G. Comparison of Phonon Damping Behavior in Quantum Dots Capped with Organic and Inorganic Ligands. NANO LETTERS 2018; 18:3667-3674. [PMID: 29781281 DOI: 10.1021/acs.nanolett.8b00800] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Surface ligand modification of colloidal semiconductor nanocrystals has been widely used as a means of controlling photoexcited-state generation, relaxation, and coupling to the environment. While progress has been made in understanding how surface ligand modification affects the behavior of electronic states, less is known about the influence of surface ligand modification on phonon behavior, which impacts relaxation dynamics and transport phenomena. In this work, we compare the dynamics of optical and acoustic phonons in CdTe quantum dots (QDs), CdTe/CdSe core/shell QDs capped with octadecylphosphonic acid ligands, and CdTe QDs capped with Se2- to ascertain how ligand exchange from native aliphatic ligands to single-atom Se2- ligands affects phonon behavior. We use transient absorption spectroscopy and observe modulations in the kinetics of excited-state decay due to QD lattice vibrations from both optical and acoustic phonons, which we describe using the damped oscillator model. The longitudinal optical phonons have similar frequencies and damping behavior in all three samples. In contrast, the longitudinal acoustic phonon mode in the Se2--capped CdTe QDs is severely damped, much more so than in CdTe and CdTe/CdSe QDs capped with the native aliphatic ligands. We attribute these differences in the acoustic phonon behavior to the differences in how the QD dissipates vibrational energy to its surroundings as a function of ligand identity. Our results indicate that these inorganic surface-capping ligands enhance not only the electronic but also the mechanical coupling of nanocrystals with their environment.
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Affiliation(s)
- Kyle J Schnitzenbaumer
- Department of Chemistry and Biochemistry , University of Colorado , Boulder , Colorado 80309 , United States
| | - Gordana Dukovic
- Department of Chemistry and Biochemistry , University of Colorado , Boulder , Colorado 80309 , United States
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9
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Liu B, Meng Y, Ruan X, Wang F, Liu W, Song F, Wang X, Wu J, He L, Zhang R, Xu Y. Coupled relaxation channels of excitons in monolayer MoSe 2. NANOSCALE 2017; 9:18546-18551. [PMID: 29164206 DOI: 10.1039/c7nr05174c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Using ultrafast degenerate pump-probe spectroscopy, we have investigated the ultrafast exciton dynamics of monolayer MoSe2 at different pump fluences. The exciton-exciton annihilation, typically occurring tens of picoseconds after pump excitation, has been found to have a substantial correlation with the initial relaxation process dominated by the defect trapping of excitons. A new exciton-exciton annihilation model has been proposed by introducing a coupling term that accounts for the initial relaxation contribution. This coupling term can be tuned by varying the pump excitation intensity and at a high intensity it vanishes due to the full occupation of the defect states. At the same time, the final electron-hole recombination is found to be affected by the heat accumulation effect originating from the high intensity pump pulses.
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Affiliation(s)
- Bo Liu
- Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, Collaborative Innovation Center of Advanced Microstructures, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, People's Republic of China.
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10
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Nadtochenko V, Denisov N, Aybush A, Gostev F, Shelaev I, Titov A, Umanskiy S, Cherepanov AD. Ultrafast Spectroscopy of Fano-Like Resonance between Optical Phonon and Excitons in CdSe Quantum Dots: Dependence of Coherent Vibrational Wave-Packet Dynamics on Pump Fluence. NANOMATERIALS 2017; 7:nano7110371. [PMID: 29113056 PMCID: PMC5707588 DOI: 10.3390/nano7110371] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Revised: 10/25/2017] [Accepted: 10/27/2017] [Indexed: 11/16/2022]
Abstract
The main goal of the present work is to study the coherent phonon in strongly confined CdSe quantum dots (QDs) under varied pump fluences. The main characteristics of coherent phonons (amplitude, frequency, phase, spectrogram) of CdSe QDs under the red-edge pump of the excitonic band [1S(e)-1S3/2(h)] are reported. We demonstrate for the first time that the amplitude of the coherent optical longitudinal-optical (LO) phonon at 6.16 THz excited in CdSe nanoparticles by a femtosecond unchirped pulse shows a non-monotone dependence on the pump fluence. This dependence exhibits the maximum at pump fluence ~0.8 mJ/cm2. At the same time, the amplitudes of the longitudinal acoustic (LA) phonon mode at 0.55 THz and of the coherent wave packet of toluene at 15.6, 23.6 THz show a monotonic rise with the increase of pump fluence. The time frequency representation of an oscillating signal corresponding to LO phonons revealed by continuous wavelet transform (CWT) shows a profound destructive quantum interference close to the origin of distinct (optical phonon) and continuum-like (exciton) quasiparticles. The CWT spectrogram demonstrates a nonlinear chirp at short time delays, where the chirp sign depends on the pump pulse fluence. The CWT spectrogram reveals an anharmonic coupling between optical and acoustic phonons.
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Affiliation(s)
- Victor Nadtochenko
- N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Kosygina st., 4, 119991 Moscow, Russia.
- Institute of Problem of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Russia.
- Chemical Faculty, Moscow State University, Leninskie Gory, 119992 Moscow, Russia.
| | - Nikolay Denisov
- Institute of Problem of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Russia.
| | - Arseniy Aybush
- N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Kosygina st., 4, 119991 Moscow, Russia.
| | - Fedor Gostev
- N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Kosygina st., 4, 119991 Moscow, Russia.
| | - Ivan Shelaev
- N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Kosygina st., 4, 119991 Moscow, Russia.
| | - Andrey Titov
- N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Kosygina st., 4, 119991 Moscow, Russia.
| | - Stanislav Umanskiy
- N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Kosygina st., 4, 119991 Moscow, Russia.
| | - And Dmitry Cherepanov
- N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Kosygina st., 4, 119991 Moscow, Russia.
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11
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Chang IY, Kim D, Hyeon-Deuk K. Control of Multiple Exciton Generation and Electron-Phonon Coupling by Interior Nanospace in Hyperstructured Quantum Dot Superlattice. ACS APPLIED MATERIALS & INTERFACES 2017; 9:32080-32088. [PMID: 28838230 DOI: 10.1021/acsami.7b08137] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The possibility of precisely manipulating interior nanospace, which can be adjusted by ligand-attaching down to the subnanometer regime, in a hyperstructured quantum dot (QD) superlattice (QDSL) induces a new kind of collective resonant coupling among QDs and opens up new opportunities for developing advanced optoelectric and photovoltaic devices. Here, we report the first real-time dynamics simulations of the multiple exciton generation (MEG) in one-, two-, and three-dimensional (1D, 2D, and 3D) hyperstructured H-passivated Si QDSLs, accounting for thermally fluctuating band energies and phonon dynamics obtained by finite-temperature ab initio molecular dynamics simulations. We computationally demonstrated that the MEG was significantly accelerated, especially in the 3D QDSL compared to the 1D and 2D QDSLs. The MEG acceleration in the 3D QDSL was almost 1.9 times the isolated QD case. The dimension-dependent MEG acceleration was attributed not only to the static density of states but also to the dynamical electron-phonon couplings depending on the dimensionality of the hyperstructured QDSL, which is effectively controlled by the interior nanospace. Such dimension-dependent modifications originated from the short-range quantum resonance among component QDs and were intrinsic to the hyperstructured QDSL. We propose that photoexcited dynamics including the MEG process can be effectively controlled by only manipulating the interior nanospace of the hyperstructured QDSL without changing component QD size, shape, compositions, ligand, etc.
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Affiliation(s)
- I-Ya Chang
- Department of Chemistry, Kyoto University , Kyoto 606-8502, Japan
- PRESTO, Japan Science and Technology Agency , 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - DaeGwi Kim
- Department of Applied Physics, Osaka City University , Osaka 558-8585, Japan
| | - Kim Hyeon-Deuk
- Department of Chemistry, Kyoto University , Kyoto 606-8502, Japan
- PRESTO, Japan Science and Technology Agency , 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
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12
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Dong S, Lian J, Jhon MH, Chan Y, Loh ZH. Pump-Power Dependence of Coherent Acoustic Phonon Frequencies in Colloidal CdSe/CdS Core/Shell Nanoplatelets. NANO LETTERS 2017; 17:3312-3319. [PMID: 28437116 DOI: 10.1021/acs.nanolett.7b01394] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Femtosecond optical pump-probe spectroscopy resolves hitherto unobserved coherent acoustic phonons in colloidal CdSe/CdS core/shell nanoplatelets (NPLs). With increasing pump fluence, the frequency of the in-plane acoustic mode increases from 5.2 to 10.7 cm-1, whereas the frequency of the out-of-plane mode remains at ∼20 cm-1. Analysis of the oscillation phases suggests that the coherent acoustic phonon generation mechanism transitions from displacive excitation to subpicosecond Auger hole trapping with increasing pump fluence. The measurements yield Huang-Rhys parameters of ∼10-2 for both acoustic modes. The weak electron-phonon coupling strengths favor the application of NPLs in optoelectronics.
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Affiliation(s)
- Shuo Dong
- Division of Chemistry and Biological Chemistry, and Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University , 21 Nanyang Link, Singapore 637371, Singapore
| | - Jie Lian
- Institute of Materials Research & Engineering, A*STAR , 2 Fusionopolis Way, Innovis # 08-03, Singapore 138634, Singapore
| | - Mark Hyunpong Jhon
- Institute of High Performance Computing, A*STAR , 1 Fusionopolis Way, #16-16 Connexis, Singapore 138632, Singapore
| | - Yinthai Chan
- Institute of Materials Research & Engineering, A*STAR , 2 Fusionopolis Way, Innovis # 08-03, Singapore 138634, Singapore
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543, Singapore
| | - Zhi-Heng Loh
- Division of Chemistry and Biological Chemistry, and Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University , 21 Nanyang Link, Singapore 637371, Singapore
- Centre for Optical Fibre Technology, The Photonics Institute, Nanyang Technological University , 50 Nanyang Avenue, Singapore 639798, Singapore
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13
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Czerniuk T, Wigger D, Akimov AV, Schneider C, Kamp M, Höfling S, Yakovlev DR, Kuhn T, Reiter DE, Bayer M. Picosecond Control of Quantum Dot Laser Emission by Coherent Phonons. PHYSICAL REVIEW LETTERS 2017; 118:133901. [PMID: 28409974 DOI: 10.1103/physrevlett.118.133901] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2016] [Indexed: 06/07/2023]
Abstract
A picosecond acoustic pulse can be used to control the lasing emission from semiconductor nanostructures by shifting their electronic transitions. When the active medium, here an ensemble of (In,Ga)As quantum dots, is shifted into or out of resonance with the cavity mode, a large enhancement or suppression of the lasing emission can dynamically be achieved. Most interesting, even in the case when gain medium and cavity mode are in resonance, we observe an enhancement of the lasing due to shaking by coherent phonons. In order to understand the interactions of the nonlinearly coupled photon-exciton-phonon subsystems, we develop a semiclassical model and find an excellent agreement between theory and experiment.
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Affiliation(s)
- T Czerniuk
- Experimentelle Physik 2, Technische Universität Dortmund, 44221 Dortmund, Germany
| | - D Wigger
- Institut für Festkörpertheorie, Universität Münster, 48149 Münster, Germany
| | - A V Akimov
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - C Schneider
- Technische Physik, Universität Würzburg, 97074 Würzburg, Germany
| | - M Kamp
- Technische Physik, Universität Würzburg, 97074 Würzburg, Germany
| | - S Höfling
- Technische Physik, Universität Würzburg, 97074 Würzburg, Germany
- SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, United Kingdom
| | - D R Yakovlev
- Experimentelle Physik 2, Technische Universität Dortmund, 44221 Dortmund, Germany
- Ioffe Institute, Russian Academy of Sciences, 194021 St. Petersburg, Russia
| | - T Kuhn
- Institut für Festkörpertheorie, Universität Münster, 48149 Münster, Germany
| | - D E Reiter
- Institut für Festkörpertheorie, Universität Münster, 48149 Münster, Germany
| | - M Bayer
- Experimentelle Physik 2, Technische Universität Dortmund, 44221 Dortmund, Germany
- Ioffe Institute, Russian Academy of Sciences, 194021 St. Petersburg, Russia
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14
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Nienhaus L, Goings JJ, Nguyen D, Wieghold S, Lyding JW, Li X, Gruebele M. Imaging Excited Orbitals of Quantum Dots: Experiment and Electronic Structure Theory. J Am Chem Soc 2015; 137:14743-50. [PMID: 26518039 DOI: 10.1021/jacs.5b09272] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Electronically excited orbitals play a fundamental role in chemical reactivity and spectroscopy. In nanostructures, orbital shape is diagnostic of defects that control blinking, surface carrier dynamics, and other important optoelectronic properties. We capture nanometer resolution images of electronically excited PbS quantum dots (QDs) by single molecule absorption scanning tunneling microscopy (SMA-STM). Dots with a bandgap of ∼1 eV are deposited on a transparent gold surface and optically excited with red or green light to produce hot carriers. The STM tip-enhanced laser light produces a large excited-state population, and the Stark effect allows transitions to be tuned into resonance by changing the sample voltage. Scanning the QDs under laser excitation, we were able to image electronic excitation to different angular momentum states depending on sample bias. The shapes differ from idealized S- or P-like orbitals due to imperfections of the QDs. Excitation of adjacent QD pairs reveals orbital alignment, evidence for electronic coupling between dots. Electronic structure modeling of a small PbS QD, when scaled for size, reveals Stark tuning and variation in the transition moment of different parity states, supporting the simple one-electron experimental interpretation in the hot carrier limit. The calculations highlight the sensitivity of orbital density to applied field, laser wavelength, and structural fluctuations of the QD.
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Affiliation(s)
| | - Joshua J Goings
- Department of Chemistry, University of Washington , Seattle, Washington 98195, United States
| | | | - Sarah Wieghold
- Department of Chemistry, Technische Universität München , 85748 Garching, Germany
| | | | - Xiaosong Li
- Department of Chemistry, University of Washington , Seattle, Washington 98195, United States
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15
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Dong S, Trivedi D, Chakrabortty S, Kobayashi T, Chan Y, Prezhdo OV, Loh ZH. Observation of an Excitonic Quantum Coherence in CdSe Nanocrystals. NANO LETTERS 2015; 15:6875-82. [PMID: 26359970 DOI: 10.1021/acs.nanolett.5b02786] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Recent observations of excitonic coherences within photosynthetic complexes suggest that quantum coherences could enhance biological light harvesting efficiencies. Here, we employ optical pump-probe spectroscopy with few-femtosecond pulses to observe an excitonic quantum coherence in CdSe nanocrystals, a prototypical artificial light harvesting system. This coherence, which encodes the high-speed migration of charge over nanometer length scales, is also found to markedly alter the displacement amplitudes of phonons, signaling dynamics in the non-Born-Oppenheimer regime.
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Affiliation(s)
- Shuo Dong
- Division of Chemistry and Biological Chemistry, and Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University , 21 Nanyang Link, Singapore 637371, Singapore
| | - Dhara Trivedi
- Department of Physics and Astronomy, University of Rochester , Rochester, New York 14627, United States
| | - Sabyasachi Chakrabortty
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543, Singapore
| | - Takayoshi Kobayashi
- Advanced Ultrafast Laser Research Center, The University of Electro-Communications , 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan
- JST, CREST, K'Gobancho , 7 Gobancho, Chiyoda-ku, Tokyo 102-0076, Japan
- Department of Electrophysics, National Chiao-Tung University , Hsinchu 300, Taiwan
- Institute of Laser Engineering, Osaka University , 2-6 Yamada-oka, Suita, Osaka 565-0971, Japan
| | - Yinthai Chan
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543, Singapore
- Institute of Materials Research & Engineering, A*STAR , 3 Research Link, Singapore 117602, Singapore
| | - Oleg V Prezhdo
- Department of Chemistry, University of Southern California , Los Angeles, California 90089, United States
| | - Zhi-Heng Loh
- Division of Chemistry and Biological Chemistry, and Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University , 21 Nanyang Link, Singapore 637371, Singapore
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16
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Kambhampati P. On the kinetics and thermodynamics of excitons at the surface of semiconductor nanocrystals: Are there surface excitons? Chem Phys 2015. [DOI: 10.1016/j.chemphys.2014.11.008] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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17
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Sinito C, Fernée MJ, Goupalov SV, Mulvaney P, Tamarat P, Lounis B. Tailoring the exciton fine structure of cadmium selenide nanocrystals with shape anisotropy and magnetic field. ACS NANO 2014; 8:11651-11656. [PMID: 25329623 DOI: 10.1021/nn5049409] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We use nominally spheroidal CdSe nanocrystals with a zinc blende crystal structure to study how shape perturbations lift the energy degeneracies of the band-edge exciton. Nanocrystals with a low degree of symmetry exhibit splitting of both upper and lower bright state degeneracies due to valence band mixing combined with the isotropic exchange interaction, allowing active control of the level splitting with a magnetic field. Asymmetry-induced splitting of the bright states is used to reveal the entire 8-state band-edge fine structure, enabling complete comparison with band-edge exciton models.
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Affiliation(s)
- Chiara Sinito
- LP2N, Université de Bordeaux , F-33405 Talence, France
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18
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Gao F, Li Z, Wang J, Rao A, Howard IA, Abrusci A, Massip S, McNeill CR, Greenham NC. Trap-induced losses in hybrid photovoltaics. ACS NANO 2014; 8:3213-3221. [PMID: 24606110 DOI: 10.1021/nn501185h] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We investigate the loss mechanisms in hybrid photovoltaics based on blends of poly(3-hexylthiophene) with CdSe nanocrystals of various sizes. By combining the spectroscopic and electrical measurements on working devices as well as films, we identify that high trap-mediated recombination is responsible for the loss of photogenerated charge carriers in devices with small nanocrystals. In addition, we demonstrate that the reduced open-circuit voltage for devices with small nanocrystals is also caused by the traps.
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Affiliation(s)
- Feng Gao
- Cavendish Laboratory, University of Cambridge , J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom
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19
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Major TA, Lo SS, Yu K, Hartland GV. Time-Resolved Studies of the Acoustic Vibrational Modes of Metal and Semiconductor Nano-objects. J Phys Chem Lett 2014; 5:866-874. [PMID: 26274080 DOI: 10.1021/jz4027248] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Over the past decade, there have been a number of transient absorption studies of the acoustic vibrational modes of metal and semiconductor nanoparticles. This Perspective provides an overview of this work. The way that the frequencies of the observed modes depend on the size and shape of the particles is described, along with their damping. Future research directions are also discussed, especially how these measurements provide information about the way nano-objects interact with their environment.
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Affiliation(s)
- Todd A Major
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556-5670, United States
| | - Shun Shang Lo
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556-5670, United States
| | - Kuai Yu
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556-5670, United States
| | - Gregory V Hartland
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556-5670, United States
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20
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Peterson MD, Cass LC, Harris RD, Edme K, Sung K, Weiss EA. The role of ligands in determining the exciton relaxation dynamics in semiconductor quantum dots. Annu Rev Phys Chem 2013; 65:317-39. [PMID: 24364916 DOI: 10.1146/annurev-physchem-040513-103649] [Citation(s) in RCA: 107] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
This article reviews the mechanisms through which molecules adsorbed to the surfaces of semiconductor nanocrystals, quantum dots (QDs), influence the pathways for and dynamics of intra- and interband exciton relaxation in these nanostructures. In many cases, the surface chemistry of the QDs determines the competition between Auger relaxation and electronic-to-vibrational energy transfer in the intraband cooling of hot carriers, and between electron or hole-trapping processes and radiative recombination in relaxation of band-edge excitons. The latter competition determines the photoluminescence quantum yield of the nanocrystals, which is predictable through a set of mostly phenomenological models that link the surface coverage of ligands with specific chemical properties to the rate constants for nonradiative exciton decay.
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Affiliation(s)
- Mark D Peterson
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113;
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21
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Mooney J, Saari JI, Myers Kelley A, Krause MM, Walsh BR, Kambhampati P. Control of Phonons in Semiconductor Nanocrystals via Femtosecond Pulse Chirp-Influenced Wavepacket Dynamics and Polarization. J Phys Chem B 2013; 117:15651-8. [DOI: 10.1021/jp406323f] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- Jonathan Mooney
- Department
of Chemistry, McGill University, Montreal, Quebec, Canada
| | - Jonathan I. Saari
- Department
of Chemistry, McGill University, Montreal, Quebec, Canada
| | - Anne Myers Kelley
- Chemistry
and Chemical Biology, University of California at Merced, Merced, California, United States
| | - Michael M. Krause
- Department
of Chemistry, McGill University, Montreal, Quebec, Canada
| | - Brenna R. Walsh
- Department
of Chemistry, McGill University, Montreal, Quebec, Canada
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22
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Mooney J, Krause MM, Saari JI, Kambhampati P. A microscopic picture of surface charge trapping in semiconductor nanocrystals. J Chem Phys 2013; 138:204705. [DOI: 10.1063/1.4807054] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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23
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24
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Saari JI, Dias EA, Reifsnyder D, Krause MM, Walsh BR, Murray CB, Kambhampati P. Ultrafast electron trapping at the surface of semiconductor nanocrystals: excitonic and biexcitonic processes. J Phys Chem B 2012. [PMID: 23186016 DOI: 10.1021/jp307668g] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Aging of semiconductor nanocrystals (NCs) is well-known to attenuate the spontaneous photoluminescence from the band edge excitonic state by introduction of nonradiative trap states formed at the NC surface. In order to explore charge carrier dynamics dictated by the surface of the NC, femtosecond pump/probe spectroscopic experiments are performed on freshly synthesized and aged CdTe NCs. These experiments reveal fast electron trapping for aged CdTe NCs from the single excitonic state (X). Pump fluence dependence with excitonic state-resolved optical pumping enables directly populating the biexcitonic state (XX), which produces further accelerated electron trapping rates. This increase in electron trapping rate triggers coherent acoustic phonons by virtue of the ultrafast impulsive time scale of the surface trapping process. The observed trapping rates are discussed in terms of electron transfer theory.
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Affiliation(s)
- Jonathan I Saari
- Department of Chemistry, McGill University, Montreal, QC, H3A 2K6, Canada
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25
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Block SB, Yurs LA, Pakoulev AV, Selinsky RS, Jin S, Wright JC. Multiresonant Multidimensional Spectroscopy of Surface-Trapped Excitons in PbSe Quantum Dots. J Phys Chem Lett 2012; 3:2707-2712. [PMID: 26295895 DOI: 10.1021/jz300599b] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Recent work spectrally isolated and measured the quantum states associated with ultrafast relaxation from an initially excited 1S excitonic state to a lower energy state that is present in an inadequately capped PbSe quantum dot sample. The relaxed state was attributed to a surface-trapped exciton (STE). This letter reports the line-narrowed, multiresonant, two-dimensional spectrum of this sample. The multidimensional spectrum is unusual because diagonal peaks are absent, but there is a strong cross-peak between the 1S and STE transitions. Theoretical modeling provided values for the coherent and incoherent dynamics, the relative exciton and biexciton transition moments, the Coulombic coupling, and the homogeneous and inhomogeneous broadening. This work demonstrates the feasibility of using multiresonant methods to probe the quantum state dynamics of interface states in nanostructures.
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Affiliation(s)
- Stephen B Block
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Lena A Yurs
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Andrei V Pakoulev
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Rachel S Selinsky
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - Song Jin
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
| | - John C Wright
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States
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26
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Gómez-Campos FM, Califano M. Hole surface trapping in CdSe nanocrystals: dynamics, rate fluctuations, and implications for blinking. NANO LETTERS 2012; 12:4508-4517. [PMID: 22849432 DOI: 10.1021/nl3016279] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Carrier trapping is one of the main sources of performance degradation in nanocrystal-based devices. Yet the dynamics of this process is still unclear. We present a comprehensive investigation into the efficiency of hole transfer to a variety of trap sites located on the surface of the core or the shell or at the core/shell interface in CdSe nanocrystals with both organic and inorganic passivation, using the atomistic semiempirical pseudopotential approach. We separate the contribution of coupling strength and energetics in different systems and trap configurations, obtaining useful general guidelines for trapping rate engineering. We find that trapping can be extremely efficient in core-only systems, with trapping times orders of magnitude faster than radiative recombination. The presence of an inorganic shell can instead bring the trapping rates well below the typical radiative recombination rates observed in these systems.
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Affiliation(s)
- Francisco M Gómez-Campos
- Departamento de Electrónica y Tecnología de Computadores, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain
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27
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Lo SS, Major TA, Petchsang N, Huang L, Kuno MK, Hartland GV. Charge carrier trapping and acoustic phonon modes in single CdTe nanowires. ACS NANO 2012; 6:5274-5282. [PMID: 22559050 DOI: 10.1021/nn3010526] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Semiconductor nanostructures produced by wet chemical synthesis are extremely heterogeneous, which makes single particle techniques a useful way to interrogate their properties. In this paper the ultrafast dynamics of single CdTe nanowires are studied by transient absorption microscopy. The wires have lengths of several micrometers and lateral dimensions on the order of 30 nm. The transient absorption traces show very fast decays, which are assigned to charge carrier trapping into surface defects. The time constants vary for different wires due to differences in the energetics and/or density of surface trap sites. Measurements performed at the band edge compared to the near-IR give slightly different time constants, implying that the dynamics for electron and hole trapping are different. The rate of charge carrier trapping was observed to slow down at high carrier densities, which was attributed to trap-state filling. Modulations due to the fundamental and first overtone of the acoustic breathing mode were also observed in the transient absorption traces. The quality factors for these modes were similar to those measured for metal nanostructures, and indicate a complex interaction with the environment.
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Affiliation(s)
- Shun Shang Lo
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556-5670, USA
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28
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Marceddu M, Saba M, Quochi F, Lai A, Huang J, Talapin DV, Mura A, Bongiovanni G. Charged excitons, Auger recombination and optical gain in CdSe/CdS nanocrystals. NANOTECHNOLOGY 2012; 23:015201. [PMID: 22156236 DOI: 10.1088/0957-4484/23/1/015201] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
CdSe/CdS colloidal nanocrystals are members of a novel class of light-emitting nanoparticles with remarkable optical properties such as suppressed fluorescence blinking and enhanced emission from multiexciton states. These properties have been linked to the suppression of non-radiative Auger recombination. In this work we employ ultrafast spectroscopy techniques to identify optical signatures of neutral and charged excitonic and multiexcitonic states. We show that Auger recombination of biexcitons is not suppressed, while we observe optical gain and amplified spontaneous emission from multiexciton states and from long-lived charged-exciton states.
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Affiliation(s)
- Marco Marceddu
- Centro Grandi Strumenti d'Ateneo, Università di Cagliari, Monserrato (CA), Italy
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29
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Dworak L, Matylitsky VV, Braun M, Wachtveitl J. Coherent longitudinal-optical ground-state phonon in CdSe quantum dots triggered by ultrafast charge migration. PHYSICAL REVIEW LETTERS 2011; 107:247401. [PMID: 22243023 DOI: 10.1103/physrevlett.107.247401] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2011] [Indexed: 05/31/2023]
Abstract
We observe the CdSe longitudinal-optical ground-state phonon in the electron transfer system composed of CdSe quantum dots and methylviologen directly by femtosecond absorption spectroscopy. A significant phase shift indicates that the coherent oscillations are triggered by an ultrafast charge migration, which is the consequence of an electron transfer from the photoexcited quantum dot to the molecular acceptor methylviologen. In contrast, the observed coherent phonons in isolated quantum dots stem from the frequency modulation of the quantum dot excited-state spectrum. From the probe wavelength dependence of the longitudinal-optical phonons in the electronic ground state and excited state it is possible to determine a biexciton binding energy of 35 meV.
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Affiliation(s)
- L Dworak
- Institute of Physical and Theoretical Chemistry, Goethe-University Frankfurt/Main, D 60438 Frankfurt/Main, Germany
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30
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Tyagi P, Kambhampati P. False multiple exciton recombination and multiple exciton generation signals in semiconductor quantum dots arise from surface charge trapping. J Chem Phys 2011; 134:094706. [DOI: 10.1063/1.3561063] [Citation(s) in RCA: 150] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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