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Huang Z, Miyashita T, Tang ML. Photon Upconversion at Organic-Inorganic Interfaces. Annu Rev Phys Chem 2024; 75:329-346. [PMID: 38382565 DOI: 10.1146/annurev-physchem-090722-011335] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/23/2024]
Abstract
Photon upconversion is a process that combines low-energy photons to form useful high-energy photons. There are potential applications in photovoltaics, photocatalysis, biological imaging, etc. Semiconductor quantum dots (QDs) are promising for the absorption of these low-energy photons due to the high extinction coefficient of QDs, especially in the near infrared (NIR). This allows the intriguing use of diffuse light sources such as solar irradiation. In this review, we describe the development of this organic-QD upconversion platform based on triplet-triplet annihilation, focusing on the dark exciton in QDs with triplet character. Then we introduce the underlying energy transfer steps, starting from QD triplet photosensitization, triplet exciton transport, triplet-triplet annihilation, and ending with the upconverted emission. Design principles to improve the total upconversion efficiency are presented. We end with limitations in current reports and proposed future directions. This review provides a guide for designing efficient organic-QD upconversion platforms for future applications, including overcoming the Shockley-Queisser limit for more efficient solar energy conversion, NIR-based phototherapy, and diagnostics in vivo.
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Affiliation(s)
- Zhiyuan Huang
- Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, People's Republic of China;
| | - Tsumugi Miyashita
- Department of Biomedical Engineering, University of Utah, Salt Lake City, Utah, USA;
| | - Ming Lee Tang
- Department of Chemistry, University of Utah, Salt Lake City, Utah, USA;
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2
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Arima D, Hidaka S, Yokomori S, Niihori Y, Negishi Y, Oyaizu R, Yoshinami T, Kobayashi K, Mitsui M. Triplet-Mediator Ligand-Protected Metal Nanocluster Sensitizers for Photon Upconversion. J Am Chem Soc 2024. [PMID: 38738855 DOI: 10.1021/jacs.4c03635] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/14/2024]
Abstract
Triplet-triplet annihilation photon upconversion (TTA-UC) is attracting a great deal of attention as a viable approach to exploit unutilized wavelengths of light in solar-driven devices. Recently, ligand-protected metal nanoclusters have emerged as a compelling platform for serving as triplet sensitizers for TTA-UC. In this study, we developed an atomically precise, triplet-mediator ligand (TL)-protected metal nanocluster, Au2Cu6(S-Adm)6[P(DPA)3]2 (Au2Cu6DPA; S-Adm = 1-adamanthanethiolate, DPA = 9,10-diphenylanthracene). In Au2Cu6DPA, the excitation of the Au2Cu6 core rapidly generates a metal-to-ligand charge transfer state, followed by the formation of the long-lived triplet state (approximately 150 μs) at a DPA site in the TL. By combining Au2Cu6DPA with a DPA annihilator, we achieved a red-to-blue upconversion quantum yield (ΦUCg) of 20.7 ± 0.4% (50% max.) with a low threshold excitation intensity of 36 mW cm-2 at 640 nm. This quantum yield almost reaches the maximum limit achievable using a DPA annihilator and establishes a record-setting value, outperforming previously reported nanocrystal and nanocluster sensitizers. Furthermore, strong upconversion emission based on a pseudo-first-order TTA process was observed under 1 sun illumination, indicating that the Au2Cu6DPA sensitizer holds promise for applications in solar-energy-based systems.
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Affiliation(s)
- Daichi Arima
- Department of Chemistry, College of Science, Rikkyo University, 3-34-1, Nishiikebuku road, Toshima-ku, Tokyo 171-8501, Japan
| | - Shion Hidaka
- Department of Chemistry, College of Science, Rikkyo University, 3-34-1, Nishiikebuku road, Toshima-ku, Tokyo 171-8501, Japan
| | - So Yokomori
- Department of Chemistry, College of Science, Rikkyo University, 3-34-1, Nishiikebuku road, Toshima-ku, Tokyo 171-8501, Japan
| | - Yoshiki Niihori
- Department of Applied Chemistry, Faculty of Science, Tokyo University of Science, Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
| | - Yuichi Negishi
- Department of Applied Chemistry, Faculty of Science, Tokyo University of Science, Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
| | - Ryuichi Oyaizu
- Department of Chemistry, Faculty of Science, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan
| | - Takumi Yoshinami
- Department of Chemistry, Faculty of Science, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan
| | - Kenji Kobayashi
- Department of Chemistry, Faculty of Science, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan
| | - Masaaki Mitsui
- Department of Chemistry, College of Science, Rikkyo University, 3-34-1, Nishiikebuku road, Toshima-ku, Tokyo 171-8501, Japan
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3
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Huang T, He S, Ni A, Lian T, Lee Tang M. Triplet energy transfer from quantum dots increases Ln(iii) photoluminescence, enabling excitation at visible wavelengths. Chem Sci 2024; 15:4556-4563. [PMID: 38516074 PMCID: PMC10952073 DOI: 10.1039/d3sc05408j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2023] [Accepted: 02/18/2024] [Indexed: 03/23/2024] Open
Abstract
Europium(iii) complexes are promising for bioimaging because of their long-lived, narrow emission. The photoluminescence (PL) from europium(iii) complexes is usually low. Thus, the effective utilization of low-energy light >400 nm and enhancement of PL are long-standing goals. Here, we show for the first time that 1-naphthoic acid triplet transmitter ligands bound to CdS quantum dots (QDs) and europium(iii) complexes create an energy transfer cascade that takes advantage of the strong QD absorption. This is confirmed by transient absorption spectroscopy, which shows hole mediated triplet energy transfer from QDs to 1-NCA, followed by triplet transfer from 1-NCA to europium(iii) complexes with an efficiency of 65.9 ± 7.7%. Smaller CdS QDs with a larger driving force lead to higher triplet transfer efficiency, with Eu(iii) PL intensity enhanced up to 21.4 times, the highest value ever reported. This hybrid QD system introduces an innovative approach to enhance the brightness of europium complexes.
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Affiliation(s)
- Tingting Huang
- Department of Chemistry, University of Utah Salt Lake City UT 84112 USA
| | - Sheng He
- Department of Chemistry, Emory University 1515 Dickey Drive Northeast Atlanta Georgia 30322 USA
| | - Anji Ni
- Department of Chemistry, Emory University 1515 Dickey Drive Northeast Atlanta Georgia 30322 USA
| | - Tianquan Lian
- Department of Chemistry, Emory University 1515 Dickey Drive Northeast Atlanta Georgia 30322 USA
| | - Ming Lee Tang
- Department of Chemistry, University of Utah Salt Lake City UT 84112 USA
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4
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Sullivan CM, Nienhaus L. Generating spin-triplet states at the bulk perovskite/organic interface for photon upconversion. NANOSCALE 2023; 15:998-1013. [PMID: 36594272 DOI: 10.1039/d2nr05767k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Perovskite-sensitized triplet-triplet annihilation (TTA) upconversion (UC) holds potential for practical applications of solid-state UC ranging from photovoltaics to sensing and imaging technologies. As the triplet sensitizer, the underlying perovskite properties heavily influence the generation of spin-triplet states once interfaced with the organic annihilator molecule, typically polyacene derivatives. Presently, most reported perovskite TTA-UC systems have utilized rubrene doped with ∼1% dibenzotetraphenylperiflanthene (RubDBP) as the annihilator/emitter species. However, practical applications require a larger apparent anti-Stokes than is currently achievable with this system due to the inherent 0.4 eV energy loss during triplet generation. In this minireview, we present the current understanding of the triplet sensitization process at the perovskite/organic semiconductor interface and introduce additional promising annihilators based on anthracene derivatives into the discussion of future directions in perovskite-sensitized TTA-UC.
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Affiliation(s)
- Colette M Sullivan
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA.
| | - Lea Nienhaus
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA.
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5
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Sullivan CM, Nienhaus L. Recharging upconversion: revealing rubrene's replacement. NANOSCALE 2022; 14:17254-17261. [PMID: 36374134 DOI: 10.1039/d2nr05309h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
One of the major limitations of solid-state perovskite-sensitized photon upconversion to date is that the only annihilator successfully paired with the perovskite sensitizer has been rubrene, raising the question of whether this appraoch of triplet sensitization is universal or limited in scope. Additionally, the inherent energetic mismatch between the perovskite bandgap and the rubrene triplet energy has restricted the apparent anti-Stokes shift achievable in the upconversion process. To increase the apparent anti-Stokes shift for upconversion processes, anthracene derivates are of particular interest due to their higher triplet energies. Here, we demonstrate successful sensitization of the triplet state of 1-chloro-9,10-bis(phenylethynyl)anthracene using the established formamidinium methylammonium lead triiodide perovskite FA0.85MA0.15PbI3, resulting in upconverted emission at 550 nm under 780 nm excitation. We draw a direct comparison to rubrene to unravel the underlying differences in the upconversion processes.
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Affiliation(s)
- Colette M Sullivan
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA.
| | - Lea Nienhaus
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA.
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Weiss R, VanOrman ZA, Sullivan CM, Nienhaus L. A Sensitizer of Purpose: Generating Triplet Excitons with Semiconductor Nanocrystals. ACS MATERIALS AU 2022; 2:641-654. [PMID: 36855545 PMCID: PMC9928406 DOI: 10.1021/acsmaterialsau.2c00047] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/21/2022] [Revised: 07/25/2022] [Accepted: 07/26/2022] [Indexed: 11/28/2022]
Abstract
The process of photon upconversion promises importance for many optoelectronic applications, as it can result in higher efficiencies and more effective photon management. Upconversion via triplet-triplet annihilation (TTA) occurs at low incident powers and at high efficiencies, requirements for integration into existing optoelectronic devices. Semiconductor nanocrystals are a diverse class of triplet sensitizers with advantages over traditional molecular sensitizers such as energetic tunability and minimal energy loss during the triplet sensitization process. In this Perspective, we review current progress in semiconductor nanocrystal triplet sensitization, specifically focusing on the nanocrystal, the ligand shell which surrounds the nanocrystal, and progress in solid-state sensitization. Finally, we discuss potential areas of improvement which could result in more efficient upconversion systems sensitized by semiconductor nanocrystals. Specifically, we focus on the development of solid-state TTA upconversion systems, elucidation of the energy transfer mechanisms from nanocrystal to transmitter ligand which underpin the upconversion process and propose novel configurations of nanocrystal-sensitized systems.
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DuBose JT, Kamat PV. Energy Versus Electron Transfer: Managing Excited-State Interactions in Perovskite Nanocrystal-Molecular Hybrids. Chem Rev 2022; 122:12475-12494. [PMID: 35793168 DOI: 10.1021/acs.chemrev.2c00172] [Citation(s) in RCA: 28] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Energy and electron transfer processes in light harvesting assemblies dictate the outcome of the overall light energy conversion process. Halide perovskite nanocrystals such as CsPbBr3 with relatively high emission yield and strong light absorption can transfer singlet and triplet energy to surface-bound acceptor molecules. They can also induce photocatalytic reduction and oxidation by selectively transferring electrons and holes across the nanocrystal interface. This perspective discusses key factors dictating these excited-state pathways in perovskite nanocrystals and the fundamental differences between energy and electron transfer processes. Spectroscopic methods to decipher between these complex photoinduced pathways are presented. A basic understanding of the fundamental differences between the two excited deactivation processes (charge and energy transfer) and ways to modulate them should enable design of more efficient light harvesting assemblies with semiconductor and molecular systems.
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Affiliation(s)
- Jeffrey T DuBose
- Radiation Laboratory, University of Notre Dame, Notre Dame, Indiana 46556, United States.,Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States
| | - Prashant V Kamat
- Radiation Laboratory, University of Notre Dame, Notre Dame, Indiana 46556, United States.,Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States.,Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556, United States
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Miyashita T, Jaimes P, Lian T, Tang ML, Xu Z. Quantifying the Ligand-Induced Triplet Energy Transfer Barrier in a Quantum Dot-Based Upconversion System. J Phys Chem Lett 2022; 13:3002-3007. [PMID: 35347991 DOI: 10.1021/acs.jpclett.2c00514] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
During photon upconversion, quantum dots (QDs) transfer energy to molecules in solution through a long ligand shell. This insulating ligand shell imparts colloidal stability at the expense of efficient photosensitization. For the first time, we quantify the barrier these aliphatic ligands pose for triplet energy transfer in solution. Using transient absorption spectroscopy, we experimentally measure a small damping coefficient of 0.027 Å-1 for a ligand exceeding 10 carbons in length. The dynamic nature of ligands in solution lowers the barrier to charge or energy transfer compared to organic thin films. In addition, we show that surface ligands shorter than 8 carbons in length allow direct energy transfer from the QD, bypassing the need for a transmitter ligand to mediate energy transfer, leading to a 6.9% upconversion quantum yield compared with 0.01% for ligands with 18 carbons. This experimentally derived insight will enable the design of efficient QD-based photosensitizers for catalysis and energy conversion.
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Affiliation(s)
- Tsumugi Miyashita
- Department of Biomedical Engineering, University of Utah, Salt Lake City, Utah 84112, United States
- Department of Bioengineering, University of California, Riverside, Riverside, California 92521, United States
| | - Paulina Jaimes
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
- Department of Materials Science and Engineering, University of California, Riverside, Riverside, California 92521, United States
| | - Tianquan Lian
- Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
| | - Ming Lee Tang
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
- Department of Materials Science and Engineering, University of California, Riverside, Riverside, California 92521, United States
- Department of Chemistry, University of California, Riverside, Riverside, California 92521, United States
| | - Zihao Xu
- Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
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9
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Imperiale CJ, Green PB, Hasham M, Wilson MWB. Ultra-small PbS nanocrystals as sensitizers for red-to-blue triplet-fusion upconversion. Chem Sci 2021; 12:14111-14120. [PMID: 34760195 PMCID: PMC8565365 DOI: 10.1039/d1sc04330g] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2021] [Accepted: 09/28/2021] [Indexed: 11/21/2022] Open
Abstract
Photon upconversion is a strategy to generate high-energy excitations from low-energy photon input, enabling advanced architectures for imaging and photochemistry. Here, we show that ultra-small PbS nanocrystals can sensitize red-to-blue triplet-fusion upconversion with a large anti-Stokes shift (ΔE = 1.04 eV), and achieve max-efficiency upconversion at near-solar fluences (I th = 220 mW cm-2) despite endothermic triplet sensitization. This system facilitates the photo-initiated polymerization of methyl methacrylate using only long-wavelength light (λ exc: 637 nm); a demonstration of nanocrystal-sensitized upconversion photochemistry. Time-resolved spectroscopy and kinetic modelling clarify key loss channels, highlighting the benefit of long-lifetime nanocrystal sensitizers, but revealing that many (48%) excitons that reach triplet-extracting carboxyphenylanthracene ligands decay before they can transfer to free-floating acceptors-emphasizing the need to address the reduced lifetimes that we determine for molecular triplets near the nanocrystal surface. Finally, we find that the inferred thermodynamics of triplet sensitization from these ultra-small PbS quantum dots are surprisingly favourable-completing an advantageous suite of properties for upconversion photochemistry-and do not vary significantly across the ensemble, which indicates minimal effects from nanocrystal heterogeneity. Together, our demonstration and study of red-to-blue upconversion using ultra-small PbS nanocrystals in a quasi-equilibrium, mildly endothermic sensitization scheme offer design rules to advance implementations of triplet fusion, especially where large anti-Stokes wavelength shifts are sought.
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Affiliation(s)
| | - Philippe B Green
- University of Toronto, Department of Chemistry Toronto ON M5S 3H6 Canada
| | - Minhal Hasham
- University of Toronto, Department of Chemistry Toronto ON M5S 3H6 Canada
| | - Mark W B Wilson
- University of Toronto, Department of Chemistry Toronto ON M5S 3H6 Canada
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10
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Rigsby EM, Miyashita T, Fishman DA, Roberts ST, Tang ML. CdSe nanocrystal sensitized photon upconverting film. RSC Adv 2021; 11:31042-31046. [PMID: 35498919 PMCID: PMC9041432 DOI: 10.1039/d1ra06562a] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2021] [Accepted: 09/10/2021] [Indexed: 12/25/2022] Open
Abstract
Here, films using CdSe nanocrystal (NC) triplet photosensitizers in conjunction with diphenylanthracene (DPA) emitters were assembled to address several challenges to practical applications for solution-based photon upconversion. By using poly(9-vinylcarbazole) as a phosphorescent host in this film, volatile organic solvents are eliminated, the spontaneous crystallization of the emitter is significantly retarded, and ∼1.5% photon upconversion quantum yield (out of a maximum of 50%) is obtained. Transient absorption spectroscopy on nanosecond-to-microsecond time scales reveals this efficiency is enabled by an exceptionally long triplet lifetime of 3.4 ± 0.3 ms. Ultimately, we find the upconversion efficiency is limited by incomplete triplet–triplet annihilation, which occurs with a rate 3–4 orders of magnitude slower than in solution-phase upconversion systems. Here, films using CdSe nanocrystal (NC) triplet photosensitizers in conjunction with diphenylanthracene (DPA) emitters doe for the conversion of green to blue light.![]()
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Affiliation(s)
- Emily M Rigsby
- Department of Chemistry, University of California Riverside Riverside CA 92521 USA
| | - Tsumugi Miyashita
- Department of Bioengineering, University of California Riverside Riverside CA 92521 USA
| | - Dmitry A Fishman
- Department of Chemistry, University of California Irvine California 92697 USA
| | - Sean T Roberts
- Department of Chemistry, University of Texas at Austin Austin TX 78712 USA
| | - Ming L Tang
- Department of Chemistry, University of California Riverside Riverside CA 92521 USA
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11
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Ehrler B, Yanai N, Nienhaus L. Up- and down-conversion in molecules and materials. J Chem Phys 2021; 154:070401. [PMID: 33607873 DOI: 10.1063/5.0045323] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Bruno Ehrler
- Center for Nanophotonics, AMOLF, 1098 XG Amsterdam, The Netherlands
| | - Nobuhiro Yanai
- Department of Chemistry and Biochemistry, Graduate School of Engineering, Center for Molecular Systems (CMS), Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka 819-0395, Japan
| | - Lea Nienhaus
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, USA
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12
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Xu Z, Huang Z, Jin T, Lian T, Tang ML. Mechanistic Understanding and Rational Design of Quantum Dot/Mediator Interfaces for Efficient Photon Upconversion. Acc Chem Res 2021; 54:70-80. [PMID: 33141563 DOI: 10.1021/acs.accounts.0c00526] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The semiconductor-nanocrystal-sensitized, three-component upconversion system has made great strides over the past 5 years. The three components (i.e., triplet photosensitizer, mediator, and emitter) each play critical roles in determining the input and output photon energy and overall quantum efficiency (QE). The nanocrystal photosensitizer converts the absorbed photon into singlet excitons and then triplet excitons via intersystem crossing. The mediator accepts the triplet exciton via either direct Dexter-type triplet energy transfer (TET) or sequential charge transfer (CT) while extending the exciton lifetime. Through a second triplet energy-transfer step from the mediator to the emitter, the latter is populated in its lowest excited triplet state. Triplet-triplet annihilation (TTA) between two triplet emitters generates the emitter in its bright singlet state, which then emits the upconverted photon. Quantum dots (QD) have a tunable band gap, large extinction coefficient, and small singlet-triplet energy losses compared to metal-ligand charge-transfer complexes. This high triplet exciton yield makes QDs good candidates for photosensitizers. In terms of driving triplet energy transfer, the triplet energy of the mediator should be slightly lower than the triplet exciton energy of the QD sensitizer for a downhill energy landscape with minimal energy loss. The same energy cascade is also required for the transfer from the mediator to the emitter. Finally, the triplet energy of the emitter must be slightly larger than one-half of its singlet energy to ensure that TTA is exothermic. Optimization of the sensitizer, mediator, and emitter will lead to an increase in the anti-Stokes shift and the total quantum efficiency. Evaluating each individual step's efficiency and kinetics is necessary for the understanding of the limiting factors in existing systems.This review summarizes chalcogenide QD-based photon upconversion systems with a focus on the mechanistic aspects of triplet energy transfer conducted by the Tang and Lian groups. Via time-resolved spectroscopy, the rates and major loss pathways associated with the two triplet energy-transfer steps were identified. The studies are focused on the near-infrared (NIR) to visible (VIS) PbS-tetracene-based systems as they allow systematic control of the QD, mediator, and emitter. Our results show that the mediator triplet state is mostly formed by direct TET from the QD and the transfer rate is influenced by the density of bound mediator molecules. Charge transfer, a loss pathway, does not produce triplet excitons and can be minimized by adding an inert shell to the QD. This transfer rate decreases exponentially with the distance between the QD and mediator molecule. The second TET rate was found to be much slower than the diffusion-limited collision rate, which results in the triplet lifetime of the mediator being the main factor limiting its efficiency. Finally, the total quantum efficiency can be calculated using these measured quantities including the TET1 and TET2 efficiencies. The agreement between calculated and measured quantum efficiencies suggests a firm understanding of QD-sensitized photon upconversion. We believe the above conclusions are general and should be widely applicable to similar systems, including singlet fission in hybrid organic-nanocrystal materials.
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Affiliation(s)
- Zihao Xu
- Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
| | - Zhiyuan Huang
- Department of Chemistry, University of California—Riverside, Riverside, California 92521, United States
| | - Tao Jin
- Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
| | - Tianquan Lian
- Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
| | - Ming L. Tang
- Department of Chemistry, University of California—Riverside, Riverside, California 92521, United States
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