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Mondal P, Sathiyamani S, Das S, Viswanatha R. Electronic structure study of dual-doped II-VI semiconductor quantum dots towards single-source white light emission. NANOSCALE 2023; 15:15288-15297. [PMID: 37681636 DOI: 10.1039/d3nr03542e] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/09/2023]
Abstract
Single-source white light emitting colloidal semiconductor quantum dots (QDs) is one of the most exciting and promising high-quality solid-state light sources to meet the current global demand for sustainable resources. While most of the previous methods involve dual (green-red) emissive nanostructures coated on blue LEDs to achieve white light, this work describes a single-source white light emitter of robust and superior quality using dual-doping. A modified synthesis method for intense white light emitting Cu, Mn dual-doped ZnSe QDs is engineered such that the extent of doping and concentration of ligands can alter their electronic structures. This is then customized to obtain various types of white light emissions ranging from warm white to cool white. Further, the composition-driven change in the electronic structure of the host QDs is exploited to achieve emission tunability over the entire visible range.
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Affiliation(s)
- Payel Mondal
- New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560064, India.
| | - Sowmeya Sathiyamani
- New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560064, India.
| | - Subham Das
- New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560064, India.
| | - Ranjani Viswanatha
- New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560064, India.
- International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560064, India
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2
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Abstract
Colloidal semiconductor nanocrystals have generated tremendous interest because of their solution processability and robust tunability. Among such nanocrystals, the colloidal quantum dot (CQD) draws the most attention for its well-known quantum size effects. In the last decade, applications of CQDs have been booming in electronics and optoelectronics, especially in photovoltaics. Electronically doped semiconductors are critical in the fabrication of solar cells, because carefully designed band structures are able to promote efficient charge extraction. Unlike conventional semiconductors, diffusion and ion implantation technologies are not suitable for doping CQDs. Therefore, researchers have creatively developed alternative doping methods for CQD materials and devices. In order to provide a state-of-the-art summary and comprehensive understanding to this research community, we focused on various doping techniques and their applications for photovoltaics and demystify them from different perspectives. By analyzing two classes of CQDs, lead chalcogenide CQDs and perovskite CQDs, we compared different working scenarios of each technique, summarized the development in this field, and raised our own future perspectives.
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Kang Z, Lin E, Qin N, Wu J, Bao D. Bismuth Vacancy-Mediated Quantum Dot Precipitation to Trigger Efficient Piezocatalytic Activity of Bi 2WO 6 Nanosheets. ACS APPLIED MATERIALS & INTERFACES 2022; 14:11375-11387. [PMID: 35191663 DOI: 10.1021/acsami.1c23282] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Point defects in piezoelectric semiconductors play a significant role in regulating the piezocatalytic performance. However, the role of metal vacancies in piezocatalysis has been less explored than that of oxygen vacancies. Herein, Bi2WO6 (BWO) nanosheets with tunable Bi defects were synthesized using an ion exchange method. High-resolution transmission electron microscopy directly revealed the existence of Bi vacancies in the lattice of BWO nanosheets and the precipitation of Bi quasiparticles. The BWO nanosheets with the highest concentration of Bi vacancies exhibited an excellent decomposition efficiency (7.83 × 10-2 min-1) over rhodamine B under ultrasound. The phenomenon is mainly attributed to the increased charge carrier concentration as a consequence of defect energy levels. In addition, the significant enhancement of light absorption capacity caused by the surface plasmon resonance effect of quasiparticles indicates that Bi ions escape from the lattice and combine with free electrons around BWO to form Bi quantum dots, which function as electron traps to facilitate the separation of charge carriers during the piezocatalytic process. This work systematically reveals the essential affiliation of metal vacancies and surface metal clusters in piezocatalysts and verifies the significance of vacancy engineering in piezocatalytic application.
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Affiliation(s)
- Zihan Kang
- State Key Laboratory of Optoelectronic Materials and Technologies, School of Materials Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China
| | - Enzhu Lin
- State Key Laboratory of Optoelectronic Materials and Technologies, School of Materials Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China
| | - Ni Qin
- State Key Laboratory of Optoelectronic Materials and Technologies, School of Materials Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China
| | - Jiang Wu
- State Key Laboratory of Optoelectronic Materials and Technologies, School of Materials Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China
| | - Dinghua Bao
- State Key Laboratory of Optoelectronic Materials and Technologies, School of Materials Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China
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Mondal P, Viswanatha R. Insights into the Oxidation State of Cu Dopants in II-VI Semiconductor Nanocrystals. J Phys Chem Lett 2022; 13:1952-1961. [PMID: 35188398 DOI: 10.1021/acs.jpclett.1c04076] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Luminescent Cu-doped semiconductor nanocrystals have played a pivotal role in the emergence of lighting and display applications for a long time. However, consensus regarding the Cu oxidation state and hence their emission mechanism has not been attained. Distinction between seemingly simple optically and magnetically active Cu2+ and inactive Cu1+ has surprisingly been the subject matter of debate in the literature for more than a decade. In this Perspective, we first discuss the fundamental quantum mechanical phenomenon explaining the optical properties of the monovalent and divalent Cu dopants. We then focus down on various techniques used to differentiate between these two fundamental mechanisms, their benefits, and their pitfalls arising in large part because of the lack of spatial separation. Hence, to obtain a cohesive story consistent with all the observations, we discuss recent results from single-molecule spectroscopy to understand the optical properties and hence the oxidation state of internally doped Cu in doped nanocrystals.
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Wang L, Cao X, Liu Z, Wang Y, xiong P, Li X, Gao W, Tang B. Dual near infrared emission in Ag2Se quantum dots via Pb doping for broadband mini light-emitting diodes. Chem Commun (Camb) 2022; 58:8432-8435. [DOI: 10.1039/d2cc02804b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Dual emission almost covering the entire NIR-II region with the maximum full width at half maximum of 542 nm was achieved by doping small amounts of Pb ions into Ag2Se...
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Makkar M, Dheer L, Singh A, Moretti L, Maiuri M, Ghosh S, Cerullo G, Waghmare UV, Viswanatha R. Magneto-Optical Stark Effect in Fe-Doped CdS Nanocrystals. NANO LETTERS 2021; 21:3798-3804. [PMID: 33904313 DOI: 10.1021/acs.nanolett.1c00126] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Fe2+ doping in II-VI semiconductors, due to the absence of energetically accessible multiple spin state configurations, has not given rise to interesting spintronic applications. In this work, we demonstrate for the first time that the interaction of homogeneously doped Fe2+ ions with the host CdS nanocrystal with no clustering is different for the two spin states and produces two magnetically inequivalent excitonic states upon optical perturbation. We combine ultrafast transient absorption spectroscopy and density functional theoretical analysis within the ground and excited states to demonstrate the presence of the magneto-optical Stark effect (MOSE). The energy gap between the spin states arising due to MOSE does not decay within the time frame of observation, unlike optical and electrical Stark shifts. This demonstration provides a stepping-stone for spin-dependent applications.
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Affiliation(s)
| | | | - Anjali Singh
- Center for Study of Science, Technology and Policy, Bangalore 560094, India
| | - Luca Moretti
- IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy
| | - Margherita Maiuri
- IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy
| | - Soumen Ghosh
- IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy
| | - Giulio Cerullo
- IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy
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Makkar M, Prakash G, Viswanatha R. Crystal Facet Engineering of CoPt Quantum Dots for Diverse Colloidal Heterostructures. J Phys Chem Lett 2020; 11:6742-6748. [PMID: 32787223 DOI: 10.1021/acs.jpclett.0c01993] [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
Precise control of crystal orientation, and specifically the exposed surface, is critical for the engineering of heterostructures. Here, using CoPt as a model system, we explore the energetics to expose suitable facets to promote the required heterostructure formation. Different heterostructures are grown ranging from core/shell structure, diffused interface, dumbbell structured dimers, and embedded island structures wherein these hybrids are fabricated via micro/macrolevel facet-selective growth. The reaction conditions used to achieve such diversity starting from the same seed offer insights into the growth mechanisms of these heterostructures. Such a microscopic understanding of surface chemistry paves the way for the design of new heterostructures with exciting properties.
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Yadav AN, Bindra JK, Jakhar N, Singh K. Switching-on superparamagnetism in diluted magnetic Fe( iii) doped CdSe quantum dots. CrystEngComm 2020. [DOI: 10.1039/c9ce01391a] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Chemically prepared, 0.5% Fe(iii)-doped CdSe QDs exhibit superparamagnetism with weak ferromagnetic exchange interaction.
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Affiliation(s)
- Amar Nath Yadav
- School of Physical Sciences
- Jawaharlal Nehru University
- New Delhi-110067
- India
| | - Jasleen K. Bindra
- Department of Chemistry and Biochemistry
- Florida State University
- Tallahassee
- USA
- National High Magnetic Field Laboratory
| | - Narendra Jakhar
- Department of Physics
- University of Rajasthan
- Jaipur-302004
- India
| | - Kedar Singh
- School of Physical Sciences
- Jawaharlal Nehru University
- New Delhi-110067
- India
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Makkar M, Saha A, Khalid S, Viswanatha R. Thermodynamics of Dual Doping in Quantum Dots. J Phys Chem Lett 2019; 10:1992-1998. [PMID: 30945549 DOI: 10.1021/acs.jpclett.9b00606] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Dual doping is a powerful way to tailor the properties of semiconductor quantum dots (QDs) arising out of host-dopant and dopant-dopant interactions. Nevertheless, it has seldom been explored due to a variety of thermodynamic challenges, such as the differential bonding strength and diffusion constant within the host matrix that integrates with the host in dissimilar ways. This work discusses the challenges involved in administering them within the constraints of one host under similar conditions of temperature, time, and chemical parameters such as solubility and reactivity using CoPt-doped CdS QDs as a model system. In addition, the various forces in play, such as Kirkendall diffusion, solid- and liquid-state diffusion, hard acid soft base interaction with the host, and the effect of lattice strain due to lattice mismatch, are studied to understand the feasibility of the core to doped transformation. These findings suggest a potential approach for manipulating the properties of semiconductors by dual doping engineering.
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Affiliation(s)
| | | | - Syed Khalid
- Brookhaven National Laboratory , Upton , New York 11973-5000 , United States
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Petralanda U, De Trizio L, Gariano G, Cingolani R, Manna L, Artyukhin S. Triggering Cation Exchange Reactions by Doping. J Phys Chem Lett 2018; 9:4895-4900. [PMID: 30085683 DOI: 10.1021/acs.jpclett.8b02083] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Cation exchange (CE) reactions have emerged as a technologically important route, complementary to the colloidal synthesis, to produce nanostructures of different geometries and compositions for a variety of applications. Here it is demonstrated with first-principles simulations that an interstitial impurity cation in CdSe nanocrystals weakens nearby bonds and reduces the CE barrier in the prototypical exchange of Cd2+ ions by Ag+ ions. A Wannier function-based tight binding model is employed to quantify microscopic mechanisms that influence this behavior. To support our model, we also tested our findings in a CE experiment: both CdSe and interstitially Ag-doped CdSe nanocrystals (containing 4% of Ag+ ions per nanocrystal on average) were exposed to Pb2+ ions at room temperature and it was observed that the exchange reaction proceeds further in doped nanocrystals. The findings suggest doping as a possible route to promote CE reactions that hardly undergo exchange otherwise, for example, those in III-V semiconductor nanocrystals.
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Affiliation(s)
- Urko Petralanda
- Istituto Italiano di Tecnologia , Via Morego 30 , Genova 16163 Italy
| | - Luca De Trizio
- Istituto Italiano di Tecnologia , Via Morego 30 , Genova 16163 Italy
| | - Graziella Gariano
- Istituto Italiano di Tecnologia , Via Morego 30 , Genova 16163 Italy
| | - Roberto Cingolani
- Istituto Italiano di Tecnologia , Via Morego 30 , Genova 16163 Italy
| | - Liberato Manna
- Istituto Italiano di Tecnologia , Via Morego 30 , Genova 16163 Italy
| | - Sergey Artyukhin
- Istituto Italiano di Tecnologia , Via Morego 30 , Genova 16163 Italy
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Zhang C, Fu X, Peng Z, Gao J, Xia Y, Zhang J, Luo W, Li H, Wang Y, Zhang D. Phosphine-free synthesis and optical stabilities of composition-tuneable monodisperse ternary PbSe1−xSx alloyed nanocrystals via cation exchange. CrystEngComm 2018. [DOI: 10.1039/c7ce02114c] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Composition-tunable monodisperse PbSe1−xSx alloyed NCs were synthesized by employing the cation exchange method, which demonstrated excellent air stability.
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12
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Makkar M, Viswanatha R. Frontier challenges in doping quantum dots: synthesis and characterization. RSC Adv 2018; 8:22103-22112. [PMID: 35541736 PMCID: PMC9081084 DOI: 10.1039/c8ra03530j] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2018] [Accepted: 06/03/2018] [Indexed: 12/26/2022] Open
Abstract
Impurity doping in semiconductor quantum dots (QDs) has numerous prospects in implementing and altering their properties and technologies. Herein, we review the state-of-the-art doping techniques arising from colloidal synthesis methods. We first discuss the advantages and challenges involved in doping; we then discuss various doping techniques, including clustering of dopants as well as expulsion out of the lattice due to self-purification. Some of these techniques have been shown to open up a new generation of robust doped semiconductor quantum dots with cluster-free doping which will be suitable for various spin-based solid-state device technologies and overcome the longstanding challenges of controlled impurity doping. Further, we discuss inhibitors such as defects, clustering and interfaces, followed by current open questions. These include pathways to obtain uniform doping in the required radial position with unprecedented control over the dopant concentration and the size of the QDs. We discuss state-of-the-art doping strategies for colloidal quantum dots, their principle, advantages and challenges in implementing the strategies.![]()
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Affiliation(s)
- Mahima Makkar
- New Chemistry Unit
- Jawaharlal Nehru Centre for Advanced Scientific Research
- Bangalore 560064
- India
| | - Ranjani Viswanatha
- New Chemistry Unit
- Jawaharlal Nehru Centre for Advanced Scientific Research
- Bangalore 560064
- India
- International Centre for Materials Science
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Gariano G, Lesnyak V, Brescia R, Bertoni G, Dang Z, Gaspari R, De Trizio L, Manna L. Role of the Crystal Structure in Cation Exchange Reactions Involving Colloidal Cu 2Se Nanocrystals. J Am Chem Soc 2017. [PMID: 28644018 PMCID: PMC6105078 DOI: 10.1021/jacs.7b03706] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Stoichiometric Cu2Se nanocrystals were synthesized in either cubic or hexagonal (metastable) crystal structures and used as the host material in cation exchange reactions with Pb2+ ions. Even if the final product of the exchange, in both cases, was rock-salt PbSe nanocrystals, we show here that the crystal structure of the starting nanocrystals has a strong influence on the exchange pathway. The exposure of cubic Cu2Se nanocrystals to Pb2+ cations led to the initial formation of PbSe unselectively on the overall surface of the host nanocrystals, generating Cu2Se@PbSe core@shell nanoheterostructures. The formation of such intermediates was attributed to the low diffusivity of Pb2+ ions inside the host lattice and to the absence of preferred entry points in cubic Cu2Se. On the other hand, in hexagonal Cu2Se nanocrystals, the entrance of Pb2+ ions generated PbSe stripes "sandwiched" in between hexagonal Cu2Se domains. These peculiar heterostructures formed as a consequence of the preferential diffusion of Pb2+ ions through specific (a, b) planes of the hexagonal Cu2Se structure, which are characterized by almost empty octahedral sites. Our findings suggest that the morphology of the nanoheterostructures, formed upon partial cation exchange reactions, is intimately connected not only to the NC host material, but also to its crystal structure.
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Affiliation(s)
| | - Vladimir Lesnyak
- Physical Chemistry, TU Dresden , Bergstr. 66b, 01062 Dresden, Germany
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Saha A, Viswanatha R. Magnetism at the Interface of Magnetic Oxide and Nonmagnetic Semiconductor Quantum Dots. ACS NANO 2017; 11:3347-3354. [PMID: 28260377 DOI: 10.1021/acsnano.7b00711] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Engineering interfaces specifically in quantum dot (QD) heterostructures provide several prospects for developing multifunctional building block materials. Precise control over internal structure by chemical synthesis offers a combination of different properties in QDs and allows us to study their fundamental properties, depending on their structure. Herein, we studied the interface of magnetic/nonmagnetic Fe3O4/CdS QD heterostructures. In this work, we demonstrate the decrease in the size of the magnetic core due to annealing at high temperature by the decrease in saturation magnetization and blocking temperature. Furthermore, surprisingly, in a prominently optically active and magnetically inactive material such as CdS, we observe the presence of substantial exchange bias in spite of the nonmagnetic nature of CdS QDs. The presence of exchange bias was proven by the increase in magnetic anisotropy as well as the presence of exchange bias field (HE) during the field-cooled magnetic measurements. This exchange coupling was eventually traced to the in situ formation of a thin antiferromagnetic FeS layer at the interface. This is verified by the study of Fe local structure using X-ray absorption fine structure spectroscopy, demonstrating the importance of interface engineering in QDs.
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Affiliation(s)
- Avijit Saha
- New Chemistry Unit and ‡International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research , Jakkur, Bangalore 560064, India
| | - Ranjani Viswanatha
- New Chemistry Unit and ‡International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research , Jakkur, Bangalore 560064, India
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