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Hinterding SM, Salzmann BBV, Vonk SJW, Vanmaekelbergh D, Weckhuysen BM, Hutter EM, Rabouw FT. Single Trap States in Single CdSe Nanoplatelets. ACS NANO 2021; 15:7216-7225. [PMID: 33759503 PMCID: PMC8155320 DOI: 10.1021/acsnano.1c00481] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Trap states can strongly affect semiconductor nanocrystals, by quenching, delaying, and spectrally shifting the photoluminescence (PL). Trap states have proven elusive and difficult to study in detail at the ensemble level, let alone in the single-trap regime. CdSe nanoplatelets (NPLs) exhibit significant fractions of long-lived "delayed emission" and near-infrared "trap emission". We use these two spectroscopic handles to study trap states at the ensemble and the single-particle level. We find that reversible hole trapping leads to both delayed and trap PL, involving the same trap states. At the single-particle level, reversible trapping induces exponential delayed PL and trap PL, with lifetimes ranging from 40 to 1300 ns. In contrast with exciton PL, single-trap PL is broad and shows spectral diffusion and strictly single-photon emission. Our results highlight the large inhomogeneity of trap states, even at the single-particle level.
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Affiliation(s)
- Stijn
O. M. Hinterding
- Soft
Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 1, 3584CC Utrecht, The Netherlands
- Inorganic
Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584CG Utrecht, The Netherlands
| | - Bastiaan B. V. Salzmann
- Condensed
Matter and Interfaces, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 1, 3584CC Utrecht, The Netherlands
| | - Sander J. W. Vonk
- Soft
Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 1, 3584CC Utrecht, The Netherlands
- Inorganic
Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584CG Utrecht, The Netherlands
| | - Daniel Vanmaekelbergh
- Condensed
Matter and Interfaces, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 1, 3584CC Utrecht, The Netherlands
| | - Bert M. Weckhuysen
- Inorganic
Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584CG Utrecht, The Netherlands
| | - Eline M. Hutter
- Inorganic
Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584CG Utrecht, The Netherlands
| | - Freddy T. Rabouw
- Soft
Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 1, 3584CC Utrecht, The Netherlands
- Inorganic
Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584CG Utrecht, The Netherlands
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Sanderson WM, Wang F, Schrier J, Buhro WE, Loomis RA. Intraband Relaxation Dynamics of Charge Carriers within CdTe Quantum Wires. J Phys Chem Lett 2020; 11:4901-4910. [PMID: 32491860 DOI: 10.1021/acs.jpclett.0c01326] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The state-to-state intraband relaxation dynamics of charge carriers photogenerated within CdTe quantum wires (QWs) are characterized via transient absorption spectroscopy. Overlapping signals from the energetic-shifting of the quantum-confinement features and the occupancy of carriers in the states associated with these features are separated using the quantum-state renormalization model. Holes generated with an excitation energy of 2.75 eV reach the band edge within the instrument response of the measurement, ∼200 fs. This extremely short relaxation time is consistent with the low photoluminescence quantum yield of the QWs, ∼0.2%, and the presence of alternative relaxation pathways for the holes. The electrons relax through the different energetically available quantum-confinement states, likely via phonon coupling, with an overall rate of ∼0.6 eV ps-1.
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Affiliation(s)
- William M Sanderson
- Department of Chemistry and Institute of Materials Science and Engineering, Washington University in Saint Louis, Saint Louis, Missouri 63130, United States
| | - Fudong Wang
- Department of Chemistry and Institute of Materials Science and Engineering, Washington University in Saint Louis, Saint Louis, Missouri 63130, United States
| | - Joshua Schrier
- Department of Chemistry, Fordham University, The Bronx, New York 10458, United States
| | - William E Buhro
- Department of Chemistry and Institute of Materials Science and Engineering, Washington University in Saint Louis, Saint Louis, Missouri 63130, United States
| | - Richard A Loomis
- Department of Chemistry and Institute of Materials Science and Engineering, Washington University in Saint Louis, Saint Louis, Missouri 63130, United States
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Hinterding SM, Vonk SJW, van Harten EJ, Rabouw FT. Dynamics of Intermittent Delayed Emission in Single CdSe/CdS Quantum Dots. J Phys Chem Lett 2020; 11:4755-4761. [PMID: 32459489 PMCID: PMC7309328 DOI: 10.1021/acs.jpclett.0c01250] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2020] [Accepted: 05/27/2020] [Indexed: 05/20/2023]
Abstract
Bright and fast fluorescence makes semiconductor nanocrystals, or quantum dots (QDs), appealing for applications ranging from biomedical research to display screens. However, a few percent of their fluorescence intensity is surprisingly slow. Research into this "delayed emission" has been scarce, despite undesired consequences for some applications and potential opportunities for others. Here, we characterize the dynamics of delayed emission exhibited by individual CdSe/CdS core/shell QDs and correlate these with changes in the emission spectrum. The delayed-emission intensity from a single QD fluctuates strongly during an experiment of several minutes and is thus not always "on", implying that control over delayed emission may be possible. Periods of bright delayed emission correlate with red-shifted emission spectra. This behavior is consistent with exciton polarization by fluctuating electric fields due to diffusing surface charges, which have been known to cause spectral diffusion in QDs. Our findings thus provide a stepping stone for future efforts to control delayed emission.
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Affiliation(s)
- Stijn
O. M. Hinterding
- Soft
Condensed Matter, Utrecht University, Princetonplein 1, 3584CC Utrecht, The Netherlands
- Inorganic
Chemistry and Catalysis, Utrecht University, Universiteitsweg 99, 3584CG Utrecht, The Netherlands
| | - Sander J. W. Vonk
- Soft
Condensed Matter, Utrecht University, Princetonplein 1, 3584CC Utrecht, The Netherlands
- Inorganic
Chemistry and Catalysis, Utrecht University, Universiteitsweg 99, 3584CG Utrecht, The Netherlands
| | - Elleke J. van Harten
- Soft
Condensed Matter, Utrecht University, Princetonplein 1, 3584CC Utrecht, The Netherlands
| | - Freddy T. Rabouw
- Soft
Condensed Matter, Utrecht University, Princetonplein 1, 3584CC Utrecht, The Netherlands
- Inorganic
Chemistry and Catalysis, Utrecht University, Universiteitsweg 99, 3584CG Utrecht, The Netherlands
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Vonk SW, Fridriksson MB, Hinterding SOM, Mangnus MJJ, van Swieten TP, Grozema FC, Rabouw FT, van der Stam W. Trapping and Detrapping in Colloidal Perovskite Nanoplatelets: Elucidation and Prevention of Nonradiative Processes through Chemical Treatment. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2020; 124:8047-8054. [PMID: 32421082 PMCID: PMC7217613 DOI: 10.1021/acs.jpcc.0c02287] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2020] [Indexed: 05/05/2023]
Abstract
Metal-halide perovskite nanocrystals show promise as the future active material in photovoltaics, lighting, and other optoelectronic applications. The appeal of these materials is largely due to the robustness of the optoelectronic properties to structural defects. The photoluminescence quantum yield (PLQY) of most types of perovskite nanocrystals is nevertheless below unity, evidencing the existence of nonradiative charge-carrier decay channels. In this work, we experimentally elucidate the nonradiative pathways in CsPbBr3 nanoplatelets, before and after chemical treatment with PbBr2 that improves the PLQY. A combination of picosecond streak camera and nanosecond time-correlated single-photon counting measurements is used to probe the excited-state dynamics over 6 orders of magnitude in time. We find that up to 40% of the nanoplatelets from a synthesis batch are entirely nonfluorescent and cannot be turned fluorescent through chemical treatment. The other nanoplatelets show fluorescence, but charge-carrier trapping leads to losses that are prevented by chemical treatment. Interestingly, even without chemical treatment, some losses due to trapping are mitigated because trapped carriers spontaneously detrap on nanosecond-to-microsecond timescales. Our analysis shows that multiple nonradiative pathways are active in perovskite nanoplatelets, which are affected differently by chemical treatment with PbBr2. More generally, our work highlights that in-depth studies using a combination of techniques are necessary to understand nonradiative pathways in fluorescent nanocrystals. Such understanding is essential to optimize synthesis and treatment procedures.
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Affiliation(s)
- Sander
J. W. Vonk
- Debye
Institute for Nanomaterials Science, Utrecht
University, Princetonplein 1, 3584 CC Utrecht, The Netherlands
| | - Magnus B. Fridriksson
- Opto-Electronic
Materials Section, Faculty of Applied Sciences, Delft University of Technology, van der Maasweg 9, 2629 HZ Delft, The Netherlands
| | - Stijn O. M. Hinterding
- Debye
Institute for Nanomaterials Science, Utrecht
University, Princetonplein 1, 3584 CC Utrecht, The Netherlands
| | - Mark J. J. Mangnus
- Debye
Institute for Nanomaterials Science, Utrecht
University, Princetonplein 1, 3584 CC Utrecht, The Netherlands
| | - Thomas P. van Swieten
- Debye
Institute for Nanomaterials Science, Utrecht
University, Princetonplein 1, 3584 CC Utrecht, The Netherlands
| | - Ferdinand C. Grozema
- Opto-Electronic
Materials Section, Faculty of Applied Sciences, Delft University of Technology, van der Maasweg 9, 2629 HZ Delft, The Netherlands
| | - Freddy T. Rabouw
- Debye
Institute for Nanomaterials Science, Utrecht
University, Princetonplein 1, 3584 CC Utrecht, The Netherlands
| | - Ward van der Stam
- Opto-Electronic
Materials Section, Faculty of Applied Sciences, Delft University of Technology, van der Maasweg 9, 2629 HZ Delft, The Netherlands
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Long T, Cao J, Jiang ZJ. Predictable spectroscopic properties of type-II ZnTe/CdSe nanocrystals and electron/hole quenching. Phys Chem Chem Phys 2019; 21:5824-5833. [PMID: 30806432 DOI: 10.1039/c9cp00026g] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The spectroscopic properties of core/shell structured ZnTe/CdSe nanocrystals (NCs) have been systematically studied. By varying the ZnTe core diameter and the CdSe shell thickness, the absorption onset and the photoluminescence peak position of the ZnTe/CdSe NCs can be readily tuned over a wide range. The theoretical model based on an effective mass approximation demonstrates that the ZnTe/CdSe NCs have type II carrier localization in which the photoexcited electrons and holes are spatially separated and confined in the shell and core, respectively. The energetics of the conduction and valence bands and the bandgaps of the ZnTe/CdSe NCs are accurately predicted. The photoluminescent experiments show that electron quenchers having a large energy difference between their reduction potential and the lowest conduction band edge of the ZnTe/CdSe nanocrystals can completely quench the luminescence. Electron acceptors having a reduction potential only slightly below the conduction band edge partially quench the photoluminescence of the nanocrystals. In this case, the extent of quenching depends upon the thickness of the shell and the energy difference. Despite the confinement of photoexcited holes in the core, the photoluminescence could be still quenched by adsorbed hole quenchers. The extent of hole quenching depends upon the core size, the shell thickness and the oxidation potential of the quenchers. Basically, an increase in the core size and the shell thickness may lead to a decrease in the extent of hole quenching. The work presented here is of great interest since it can be extended to understand the spectroscopic properties and photoluminescence quenching behaviors of other core/shell semiconductor NCs.
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Affiliation(s)
- Tongqing Long
- Guangzhou Key Laboratory for Surface Chemistry of Energy Materials, New Energy Research Institute, College of Environment and Energy, South China University of Technology, Guangzhou 510006, China.
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Montanarella F, Biondi M, Hinterding SOM, Vanmaekelbergh D, Rabouw FT. Reversible Charge-Carrier Trapping Slows Förster Energy Transfer in CdSe/CdS Quantum-Dot Solids. NANO LETTERS 2018; 18:5867-5874. [PMID: 30095918 PMCID: PMC6139578 DOI: 10.1021/acs.nanolett.8b02538] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The dynamics of photoluminescence (PL) from nanocrystal quantum dots (QDs) is significantly affected by the reversible trapping of photoexcited charge carriers. This process occurs after up to 50% of the absorption events, depending on the type of QD considered, and can extend the time between the photoexcitation and relaxation of the QD by orders of magnitude. Although many optoelectronic applications require QDs assembled into a QD solid, until now, reversible trapping has been studied only in (ensembles of) spatially separated QDs. Here, we study the influence of reversible trapping on the excited-state dynamics of CdSe/CdS core/shell QDs when they are assembled into close-packed "supraparticles". Time- and spectrally resolved photoluminescence (PL) measurements reveal competition among spontaneous emission, reversible charge-carrier trapping, and Förster resonance energy transfer between the QDs. While Förster transfer causes the PL to red-shift over the first 20-50 ns after excitation, reversible trapping stops and even reverses this trend at later times. We can model this behavior with a simple kinetic Monte Carlo simulation by considering that charge-carrier trapping leaves the QDs in a state with zero oscillator strength in which no energy transfer can occur. Our results highlight that reversible trapping significantly affects the energy and charge-carrier dynamics for applications in which QDs are assembled into a QD solid.
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