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Khosla M, Rao S, Gupta S. Polarons Explain Luminescence Behavior of Colloidal Quantum Dots at Low Temperature. Sci Rep 2018; 8:8385. [PMID: 29849075 PMCID: PMC5976793 DOI: 10.1038/s41598-018-26678-w] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Accepted: 05/11/2018] [Indexed: 02/03/2023] Open
Abstract
Luminescence properties of colloidal quantum dots have found applications in imaging, displays, light-emitting diodes and lasers, and single photon sources. Despite wide interest, several experimental observations in low-temperature photoluminescence of these quantum dots, such as the short lifetime on the scale of microseconds and a zero-longitudinal optical phonon line in spectrum, both attributed to a dark exciton in literature, remain unexplained by existing models. Here we propose a theoretical model including the effect of solid-state environment on luminescence. The model captures both coherent and incoherent interactions of band-edge exciton with phonon modes. Our model predicts formation of dressed states by coupling of the exciton with a confined acoustic phonon mode, and explains the short lifetime and the presence of the zero-longitudinal optical phonon line in the spectrum. Accounting for the interaction of the exciton with bulk phonon modes, the model also explains the experimentally observed temperature-dependence of the photoluminescence decay dynamics and temperature-dependence of the photoluminescence spectrum.
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Affiliation(s)
- Meenakshi Khosla
- Department of Electrical Engineering, Indian Institute of Technology Kanpur, Kanpur, 208016, UP, India.,Department of Electrical and Computer Engineering, Cornell University, Ithaca, NY, 14850, USA
| | - Sravya Rao
- Department of Electrical Engineering, Indian Institute of Technology Kanpur, Kanpur, 208016, UP, India
| | - Shilpi Gupta
- Department of Electrical Engineering, Indian Institute of Technology Kanpur, Kanpur, 208016, UP, India.
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Lee M, Park YH, Kang EB, Chae A, Choi Y, Jo S, Kim YJ, Park SJ, Min B, An TK, Lee J, In SI, Kim SY, Park SY, In I. Highly Efficient Visible Blue-Emitting Black Phosphorus Quantum Dot: Mussel-Inspired Surface Functionalization for Bioapplications. ACS OMEGA 2017; 2:7096-7105. [PMID: 30023540 PMCID: PMC6044902 DOI: 10.1021/acsomega.7b01058] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2017] [Accepted: 10/11/2017] [Indexed: 05/28/2023]
Abstract
The preparation of blue-emitting black phosphorus quantum dots (BPQDs) is based on the liquid-phase exfoliation of bulk BP. We report the synthesis of soluble BPQDs showing a strong visible blue-light emission. Highly fluorescent (photoluminescence quantum yield of ≈5% with the maximum emission (λmax) at ≈437 nm) and dispersible BPQDs in various organic solvents are first prepared by simple ultrasonication of BP crystals in chloroform in the ambient atmosphere. Furthermore, simple mussel-inspired surface functionalization of BPQDs with catechol-grafted poly(ethylene glycol) in basic buffer afforded water-soluble blue-emitting BPQDs showing long-term fluorescence stability, very low cytotoxicity, and excellent fluorescence live cell imaging capability.
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Affiliation(s)
- Miyeon Lee
- Department
of Chemistry, KAIST, Yuseong-gu, Daejeon 34141, South Korea
| | - Young Ho Park
- Department
of Energy System Engineering, DGIST, Daegu 42988, South Korea
| | - Eun Bi Kang
- Department of Chemical
& Biological Engineering, Department of Polymer Science and
Engineering, and Department of IT Convergence (Brain Korea PLUS 21), Korea National University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27909, South Korea
| | - Ari Chae
- Department of Chemical
& Biological Engineering, Department of Polymer Science and
Engineering, and Department of IT Convergence (Brain Korea PLUS 21), Korea National University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27909, South Korea
| | - Yujin Choi
- Department of Chemical
& Biological Engineering, Department of Polymer Science and
Engineering, and Department of IT Convergence (Brain Korea PLUS 21), Korea National University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27909, South Korea
| | - Seongho Jo
- Department of Chemical
& Biological Engineering, Department of Polymer Science and
Engineering, and Department of IT Convergence (Brain Korea PLUS 21), Korea National University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27909, South Korea
| | - Yu Jin Kim
- Center for
Nanoscale Materials, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Soo-Jin Park
- Department
of Chemistry, Inha University, Incheon 402-751, South Korea
| | - Byunggak Min
- Department of Chemical
& Biological Engineering, Department of Polymer Science and
Engineering, and Department of IT Convergence (Brain Korea PLUS 21), Korea National University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27909, South Korea
| | - Tae Kyu An
- Department of Chemical
& Biological Engineering, Department of Polymer Science and
Engineering, and Department of IT Convergence (Brain Korea PLUS 21), Korea National University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27909, South Korea
| | - Jihoon Lee
- Department of Chemical
& Biological Engineering, Department of Polymer Science and
Engineering, and Department of IT Convergence (Brain Korea PLUS 21), Korea National University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27909, South Korea
| | - Su-Il In
- Department
of Energy System Engineering, DGIST, Daegu 42988, South Korea
| | - Sang Youl Kim
- Department
of Chemistry, KAIST, Yuseong-gu, Daejeon 34141, South Korea
| | - Sung Young Park
- Department of Chemical
& Biological Engineering, Department of Polymer Science and
Engineering, and Department of IT Convergence (Brain Korea PLUS 21), Korea National University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27909, South Korea
| | - Insik In
- Department of Chemical
& Biological Engineering, Department of Polymer Science and
Engineering, and Department of IT Convergence (Brain Korea PLUS 21), Korea National University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27909, South Korea
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Hafiz SA, Esteves RJA, Demchenko DO, Arachchige IU, Özgür Ü. Energy Gap Tuning and Carrier Dynamics in Colloidal Ge1-xSnx Quantum Dots. J Phys Chem Lett 2016; 7:3295-3301. [PMID: 27513723 DOI: 10.1021/acs.jpclett.6b01333] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Optical transition energies and carrier dynamics in colloidally synthesized 2.0 ± 0.8 nm Ge1-xSnx quantum dots (x = 0.055-0.236) having visible luminescence were investigated using steady-state and time-resolved photoluminescence (PL) spectroscopy supported by first-principles calculations. By changing Sn content from x = 0.055 to 0.236, experimentally determined HOMO-LUMO gap at 15 K was tuned from 1.88 to 1.61 eV. Considering the size and compositional variations, these values were consistent with theoretically calculated ones. At 15 K, time-resolved PL revealed slow decay of luminescence (3-27 μs), likely due to the recombination of spin-forbidden dark excitons and recombination of carriers trapped at surface states. Increasing Sn concentration to 23.6% led to 1 order of magnitude faster recombination. At 295 K, PL decays were 3 orders of magnitude faster (9-28 ns) owing to the thermal activation of bright excitons and carrier detrapping from surface states.
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Affiliation(s)
- Shopan A Hafiz
- Department of Electrical and Computer Engineering, Virginia Commonwealth University , Richmond, Virginia 23284, United States
| | - Richard J Alan Esteves
- Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284, United States
| | - Denis O Demchenko
- Department of Physics, Virginia Commonwealth University , Richmond, Virginia 23284, United States
| | - Indika U Arachchige
- Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284, United States
| | - Ümit Özgür
- Department of Electrical and Computer Engineering, Virginia Commonwealth University , Richmond, Virginia 23284, United States
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Zhang Y, Ersoy O, Karatutlu A, Little W, Sapelkin A. Local structure of Ge quantum dots determined by combined numerical analysis of EXAFS and XANES data. JOURNAL OF SYNCHROTRON RADIATION 2016; 23:253-259. [PMID: 26698071 DOI: 10.1107/s160057751501913x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2015] [Accepted: 10/10/2015] [Indexed: 06/05/2023]
Abstract
The sensitivity of X-ray absorption near-edge structure (XANES) to the local symmetry has been investigated in small (∼4 nm) matrix-free Ge quantum dots. The FDMNES package was used to calculate the theoretical XANES spectra that were compared with the experimental data of as-prepared and annealed nanoparticles. It was found that XANES data for an as-prepared sample can only be adequately described if the second coordination shell of the diamond-type structural model is included in the FDMNES calculations. This is in contrast to the extended X-ray absorption fine-structure data that show only the first-shell signal. These results suggest that, despite the high degree of disorder and a large surface-to-volume ratio, as-prepared small Ge quantum dots retain the diamond-type symmetry beyond the first shell. Furthermore, we utilized this sensitivity of XANES to the local symmetry to study annealed Ge quantum dots and found evidence for significant structural distortion which we attribute to the existence of surface disorder in the annealed oxygen-free Ge quantum dots.
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Affiliation(s)
- Yuanpeng Zhang
- School of Physics and Astronomy, Queen Mary, University of London, Mile End Road, London E1 4NS, UK
| | - Osman Ersoy
- School of Physics and Astronomy, Queen Mary, University of London, Mile End Road, London E1 4NS, UK
| | - Ali Karatutlu
- School of Physics and Astronomy, Queen Mary, University of London, Mile End Road, London E1 4NS, UK
| | - William Little
- School of Physics and Astronomy, Queen Mary, University of London, Mile End Road, London E1 4NS, UK
| | - Andrei Sapelkin
- School of Physics and Astronomy, Queen Mary, University of London, Mile End Road, London E1 4NS, UK
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Millo O, Balberg I, Azulay D, Purkait TK, Swarnakar AK, Rivard E, Veinot JGC. Direct Evaluation of the Quantum Confinement Effect in Single Isolated Ge Nanocrystals. J Phys Chem Lett 2015; 6:3396-3402. [PMID: 26275992 DOI: 10.1021/acs.jpclett.5b01541] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
To address the yet open question regarding the nature of quantum confinement in Ge nanocrystals (Ge NCs) we employed scanning tunneling spectroscopy to monitor the electronic structure of individual isolated Ge NCs as a function of their size. The (single-particle) band gaps extracted from the tunneling spectra increase monotonically with decreasing nanocrystal size, irrespective of the capping ligands, manifesting the effect of quantum confinement. Band-gap widening of ∼1 eV with respect to the bulk value was observed for Ge-NCs 3 nm in diameter. The picture emerging from comparison with theoretical calculations and other experimental results is discussed.
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Affiliation(s)
- Oded Millo
- Racah Institute of Physics and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem , Jerusalem 91904, Israel
| | - Isacc Balberg
- Racah Institute of Physics and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem , Jerusalem 91904, Israel
| | - Doron Azulay
- Racah Institute of Physics and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem , Jerusalem 91904, Israel
| | - Tapas K Purkait
- Department of Chemistry, University of Alberta , 11227 Saskatchewan Drive NW, Edmonton, Alberta T6G 2G2, Canada
| | - Anindya K Swarnakar
- Department of Chemistry, University of Alberta , 11227 Saskatchewan Drive NW, Edmonton, Alberta T6G 2G2, Canada
| | - Eric Rivard
- Department of Chemistry, University of Alberta , 11227 Saskatchewan Drive NW, Edmonton, Alberta T6G 2G2, Canada
| | - Jonathan G C Veinot
- Department of Chemistry, University of Alberta , 11227 Saskatchewan Drive NW, Edmonton, Alberta T6G 2G2, Canada
- NRC-National Institute for Nanotechnology , 11421 Saskatchewan Drive NW, Edmonton, Alberta T6G 2M9, Canada
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