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Steves MA, Zheng H, Knappenberger KL. Correlated spatially resolved two-dimensional electronic and linear absorption spectroscopy. OPTICS LETTERS 2019; 44:2117-2120. [PMID: 30985825 DOI: 10.1364/ol.44.002117] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Accepted: 03/25/2019] [Indexed: 06/09/2023]
Abstract
A multimodal method for correlating linear and nonlinear optical spectra with a spatial resolution is presented. Using a partially collinear pump-probe geometry and two-frame phase-cycling, ultrafast two-dimensional electronic spectroscopy (2DES) was performed with transverse-spatial and temporal resolutions of 17 μm and 80 fs, respectively. Time-resolved 2DES maps were spatially correlated with linear extinction spectra obtained in the same imaging platform, enabling the examination of state-resolved dynamics of spatially heterogeneous materials. Thin films of aggregated CdSe nanocrystals were studied to demonstrate the combined spectral, temporal, and imaging capabilities of this method.
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2
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Ashner MN, Winslow SW, Swan JW, Tisdale WA. Markov Chain Monte Carlo Sampling for Target Analysis of Transient Absorption Spectra. J Phys Chem A 2019; 123:3893-3902. [DOI: 10.1021/acs.jpca.9b00873] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Matthew N. Ashner
- Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
| | - Samuel W. Winslow
- Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
| | - James W. Swan
- Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
| | - William A. Tisdale
- Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
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Xu J, Tong X, Yu P, Wenya GE, McGrath T, Fong MJ, Wu J, Wang ZM. Ultrafast Dynamics of Charge Transfer and Photochemical Reactions in Solar Energy Conversion. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2018; 5:1800221. [PMID: 30581691 PMCID: PMC6299728 DOI: 10.1002/advs.201800221] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2018] [Revised: 08/05/2018] [Indexed: 05/31/2023]
Abstract
For decades, ultrafast time-resolved spectroscopy has found its way into an increasing number of applications. It has become a vital technique to investigate energy conversion processes and charge transfer dynamics in optoelectronic systems such as solar cells and solar-driven photocatalytic applications. The understanding of charge transfer and photochemical reactions can help optimize and improve the performance of relevant devices with solar energy conversion processes. Here, the fundamental principles of photochemical and photophysical processes in photoinduced reactions, in which the fundamental charge carrier dynamic processes include interfacial electron transfer, singlet excitons, triplet excitons, excitons fission, and recombination, are reviewed. Transient absorption (TA) spectroscopy techniques provide a good understanding of the energy/electron transfer processes. These processes, including excited state generation and interfacial energy/electron transfer, are dominate constituents of solar energy conversion applications, for example, dye-sensitized solar cells and photocatalysis. An outlook for intrinsic electron/energy transfer dynamics via TA spectroscopic characterization is provided, establishing a foundation for the rational design of solar energy conversion devices.
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Affiliation(s)
- Jing‐Yin Xu
- Institute of Fundamental and Frontier SciencesUniversity of Electronic Science and Technology of ChinaChengdu610054P. R. China
| | - Xin Tong
- Institute of Fundamental and Frontier SciencesUniversity of Electronic Science and Technology of ChinaChengdu610054P. R. China
| | - Peng Yu
- Institute of Fundamental and Frontier SciencesUniversity of Electronic Science and Technology of ChinaChengdu610054P. R. China
| | - Gideon Evans Wenya
- Institute of Fundamental and Frontier SciencesUniversity of Electronic Science and Technology of ChinaChengdu610054P. R. China
| | - Thomas McGrath
- Department of PhysicsLancaster UniversityLancasterLancashireLA14YWUK
| | | | - Jiang Wu
- Institute of Fundamental and Frontier SciencesUniversity of Electronic Science and Technology of ChinaChengdu610054P. R. China
- Department of Electronic and Electrical EngineeringUniversity College LondonTorrington PlaceLondonWC1E7JEUK
| | - Zhiming M. Wang
- Institute of Fundamental and Frontier SciencesUniversity of Electronic Science and Technology of ChinaChengdu610054P. R. China
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Fisher AAE, Osborne MA. Sizing Up Excitons in Core-Shell Quantum Dots via Shell-Dependent Photoluminescence Blinking. ACS NANO 2017; 11:7829-7840. [PMID: 28679040 DOI: 10.1021/acsnano.7b01978] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Semiconductor nanocrystals or quantum dots (QDs) are now widely used across solar cell, display, and bioimaging technologies. While advances in multishell, alloyed, and multinary core-shell QD structures have led to improved light-harvesting and photoluminescence (PL) properties of these nanomaterials, the effects that QD-capping have on the exciton dynamics that govern PL instabilities such as blinking in single-QDs is not well understood. We report experimental measurements of shell-size-dependent absorption and PL intermittency in CdSe-CdS QDs that are consistent with a modified charge-tunnelling, self-trapping (CTST) description of the exciton dynamics in these nanocrystals. By introducing an effective, core-exciton size, which accounts for delocalization of charge carriers across the QD core and shell, we show that the CTST models both the shell-depth-dependent red-shift of the QD band gap and changes in the on/off-state switching statistics that we observe in single-QD PL intensity trajectories. Further analysis of CdSe-ZnS QDs, shows how differences in shell structure and integrity affect the QD band gap and PL blinking within the CTST framework.
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Affiliation(s)
- Aidan A E Fisher
- Department of Chemistry, School of Life Sciences, University of Sussex , Falmer, Brighton BN1 9QJ, United Kingdom
| | - Mark A Osborne
- Department of Chemistry, School of Life Sciences, University of Sussex , Falmer, Brighton BN1 9QJ, United Kingdom
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Jarrett JW, Yi C, Stoll T, Rehault J, Oriana A, Branchi F, Cerullo G, Knappenberger KL. Dissecting charge relaxation pathways in CdSe/CdS nanocrystals using femtosecond two-dimensional electronic spectroscopy. NANOSCALE 2017; 9:4572-4577. [PMID: 28321446 DOI: 10.1039/c7nr00654c] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Exciton relaxation dynamics of CdSe and quasi-type-II CdSe/CdS core/shell nanocrystals were examined using femtosecond two-dimensional electronic spectroscopy (2DES). The use of 2DES allowed for determination of structure-specific and state-resolved carrier dynamics for CdSe nanocrystals formed with five, or fewer, CdS passivation monolayers (ML). For CdSe and CdSe/CdS nanocrystals formed with one through three MLs of CdS, excitation using broad bandwidth femtosecond visible laser pulses generated electron-hole pairs among the |X1〉 = 2.14 eV and |X2〉 = 2.27 eV exciton states. For both excitations, the electron is promoted to the lowest energy excited (1Se) conduction-band state and the hole is in the 1S3/2 (X1) or 2S3/2 (X2) valence-band state. Therefore, the relaxation dynamics of the hot hole were isolated by monitoring the-time-dependent amplitude of 2DES cross peaks. The time constant for hot hole relaxation within the CdSe valence band was 150 ± 45 fs. Upon passivation by CdS, this hole relaxation time constant increased to 170 ± 30 fs (CdSe/CdS-3ML). This small increase was attributed to the formation of a graded, or alloyed, interfacial region that precedes the growth of a uniform CdS capping layer. The small increase in hole relaxation time reflects the larger nanocrystal volume of the CdSe/CdS system with respect to the CdSe nanocrystal core. In contrast, the dynamics of larger core/shell nanocrystals (≥4ML CdS) exhibited a picosecond buildup in 2DES cross-peak amplitude. This time-dependent response was attributed to interfacial hole transfer from CdS to CdSe valence-band states. Importantly, the 2DES data distinguish CdSe exciton relaxation from interfacial carrier transfer dynamics. In combination, isolation of structurally well-defined nanocrystals and state-resolved 2DES can be used to examine directly the influence of nanoscale structural modifications on electronic carrier dynamics, which are critical for developing nanocluster-based photonic devices.
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Affiliation(s)
- J W Jarrett
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306-4390, USA.
| | - C Yi
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306-4390, USA.
| | - T Stoll
- IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy
| | - J Rehault
- IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy and Paul Scherrer Institute, CH-4232 Villigen PSI, Switzerland
| | - A Oriana
- IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy and Laboratoire de Spectroscopie Ultrarapide, EPFL, CH-1015 Lausanne, Switzerland
| | - F Branchi
- IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy
| | - G Cerullo
- IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy
| | - K L Knappenberger
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306-4390, USA. and IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy and National High Magnetic Field Laboratory, 1800 E. Paul Dirac Drive, Tallahassee, Florida 32310-4005, USA
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Zeng P, Kirkwood N, Mulvaney P, Boldt K, Smith TA. Shell effects on hole-coupled electron transfer dynamics from CdSe/CdS quantum dots to methyl viologen. NANOSCALE 2016; 8:10380-10387. [PMID: 27139145 DOI: 10.1039/c6nr00168h] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Electron transfer (ET) dynamics from the 1Se electron state in quasi-type II CdSe/CdS core/shell quantum dots (QDs) to adsorbed methyl viologen (MV(2+)) were measured using femtosecond transient absorption spectroscopy. The intrinsic ET rate kET was determined from the measured average number of ET-active MV(2+) per QD, which permits reliable comparisons of variant shell thickness and different hole states. The 1Se electron was extracted efficiently from the CdSe core, even for CdS shells up to 20 Å thick. The ET rate decayed exponentially from 10(10) to 10(9) s(-1) for increasing CdS shell thicknesses with an attenuation factor β≈ 0.13 Å(-1). We observed that compared to the ground state exciton 1Se1S3/2 the electron coupled to the 2S3/2 hot hole state exhibited slower ET rates for thin CdS shells. We attribute this behaviour to an Auger-assisted ET process (AAET), which depends on electron-hole coupling controlled by the CdS shell thickness.
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Affiliation(s)
- Peng Zeng
- School of Chemistry, The University of Melbourne, Parkville, Victoria 3010, Australia.
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Zhang A, Bian Y, Wang J, Chen K, Dong C, Ren J. Suppressed blinking behavior of CdSe/CdS QDs by polymer coating. NANOSCALE 2016; 8:5006-5014. [PMID: 26865498 DOI: 10.1039/c5nr08504g] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Semiconductor quantum dots (QDs) are very important fluorescent nanocrystals with excellent optical properties. However, QDs, at the single-particle level, show severe fluorescence intermittency (or blinking) on a wide time scale from milliseconds to minutes, which limits certain optical and biological applications. Generally, blinking behavior of QDs strongly depends on their surface state and surrounding environment. Therefore, current blinking suppression approaches are mostly focused on the introduction of an inorganic shell and organic small molecule compounds. In this study, we described a "bottom up" approach for the synthesis of CdSe/CdS/polymer core/shell/shell QDs via the in situ one-pot polymerization approach in order to control the blinking behavior of QDs. Three monomers (dithiothreitol (DTT), phenylenediamine (PDA), and hexamethylenediamine (HDA)) were respectively used to polymerize with hexachlorocyclotriphosphazene (HCCP), and then the polyphosphazene polymers were obtained with cyclotriphosphazene as the basic macromolecular backbone. By regulating the molar ratios of the activated comonomers, we can control the blinking behavior of CdSe/CdS/polymer QDs. Under the optimal conditions, the percentage of "non-blinking" CdSe/CdS/polymer QDs (the "on time" fraction > 99% of the overall observation time) was up to 78%. The suppression mechanism was attributed to the efficient passivation of QD surface traps by the sulfhydryl or phenyl groups in the polyphosphazene polymers.
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Affiliation(s)
- Aidi Zhang
- School of Chemistry and Chemical Engineering, State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China.
| | - Yannan Bian
- School of Chemistry and Chemical Engineering, State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China.
| | - Jinjie Wang
- School of Chemistry and Chemical Engineering, State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China.
| | - Kuiyong Chen
- School of Materials Science and Engineering, State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai, 200240, People's Republic of China
| | - Chaoqing Dong
- School of Chemistry and Chemical Engineering, State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China.
| | - Jicun Ren
- School of Chemistry and Chemical Engineering, State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China.
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