Browsing by Author "Hernández-Martínez, Pedro Ludwig"

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Open Access
Efficient generation of emissive many-body correlations in copper-doped colloidal quantum wells
(Cell Press, 2022-09-21) Yu, Junhong; Sharma, Manoj; Li, Mingjie; Liu, Baiquan; Hernández-Martínez, Pedro Ludwig; Delikanli, Savaş; Sharma, Ashma; Altintas, Yemliha; Hettiarachchi, Chathuranga; Sum, Tze Chien; Demir, Hilmi Volkan; Dang, Cuong
Colloidal quantum wells (CQWs) provide an appealing platform to achieve emissive many-body correlations for novel optoelectronic devices, given that they act as hosts for strong carrier Coulomb interactions and present suppressed Auger recombination. However, the demonstrated high-order excitonic emission in CQWs requires ultrafast pumping with high excitation levels and can only be spectrally resolved at the single-particle level under cryogenic conditions. Here, through systematic investigation using static power-dependent emission spectroscopy and transient carrier dynamics, we show that Cu-doped CdSe CQWs exhibit continuous-wave-pumped high-order excitonic emission at room temperature with a large binding energy of ∼64 meV. We attribute this unique behavior to dopant excitons in which the ultralong lifetime and the highly localized wavefunction facilitate the formation of many-body correlations. The spectrally resolved high-order excitonic emission generated at power levels compatible with solar irradiation and electrical injection might pave the way for novel solution-processed solid-state devices. © 2022 The Authors
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Interfacial charge and energy transfer in van der Waals heterojunctions
(John Wiley and Sons Inc, 2022-03) Hu, Zehua; Liu, Xue; Hernández-Martínez, Pedro Ludwig; Zhang, Shishu; Gu, Peng; Du, Wei; Xu, Weigao; Demir, Hilmi Volkan; Liu, Haiyun; Xiong, Qihua
Van der Waals heterojunctions are fast-emerging quantum structures fabricated by the controlled stacking of two-dimensional (2D) materials. Owing to the atomically thin thickness, their carrier properties are not only determined by the host material itself, but also defined by the interlayer interactions, including dielectric environment, charge trapping centers, and stacking angles. The abundant constituents without the limitation of lattice constant matching enable fascinating electrical, optical, and magnetic properties in van der Waals heterojunctions toward next-generation devices in photonics, optoelectronics, and information sciences. This review focuses on the charge and energy transfer processes and their dynamics in transition metal dichalcogenides (TMDCs), a family of quantum materials with strong excitonic effects and unique valley properties, and other related 2D materials such as graphene and hexagonal-boron nitride. In the first part, we summarize the ultrafast charge transfer processes in van der Waals heterojunctions, including its experimental evidence and theoretical understanding, the interlayer excitons at the TMDC interfaces, and the hot carrier injection at the graphene/TMDCs interface. In the second part, the energy transfer, including both Förster and Dexter types, are reviewed from both experimental and theoretical perspectives. Finally, we highlight the typical charge and energy transfer applications in photodetectors and summarize the challenges and opportunities for future development in this field. © 2022 The Authors. InfoMat published by UESTC and John Wiley & Sons Australia, Ltd.
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sp-d exchange interactions in wave function engineered colloidal CdSe/Mn: CdS Hetero-Nanoplatelets
(American Chemical Society, 2018) Muckel, F.; Delikanlı S.; Hernández-Martínez, Pedro Ludwig; Priesner, T.; Lorenz, S.; Ackermann, J.; Sharma, Manoj; Demir, Hilmi Volkan; Bacher, G.
In two-dimensional (2D) colloidal semiconductor nanoplatelets, which are atomically flat nanocrystals, the precise control of thickness and composition on the atomic scale allows for the synthesis of heterostructures with well-defined electron and hole wave function distributions. Introducing transition metal dopants with a monolayer precision enables tailored magnetic exchange interactions between dopants and band states. Here, we use the absorption based technique of magnetic circular dichroism (MCD) to directly prove the exchange coupling of magnetic dopants with the band charge carriers in hetero-nanoplatelets with CdSe core and manganese-doped CdS shell (CdSe/Mn:CdS). We show that the strength of both the electron as well as the hole exchange interactions with the dopants can be tuned by varying the nanoplatelets architecture with monolayer accuracy. As MCD is highly sensitive for excitonic resonances, excited level spectroscopy allows us to resolve and identify, in combination with wave function calculations, several excited state transitions including spin-orbit split-off excitonic contributions. Thus, our study not only demonstrates the possibility to expand the extraordinary physical properties of colloidal nanoplatelets toward magneto-optical functionality by transition metal doping but also provides an insight into the excited state electronic structure in this novel two-dimensional material.