2017 Fiscal Year Annual Research Report
One and multiple photon induced generation and stabilization of multi-excitons in quantum dot superlattices
Publicly Offered Research
| Project Area | Application of Cooperative-Excitation into Innovative Molecular Systems with High-Order Photo-functions |
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| Project/Area Number |
17H05243
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| Research Institution | Hokkaido University |
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Principal Investigator |
Biju V・Pillai 北海道大学, 電子科学研究所, 教授 (60392651)
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| Project Period (FY) |
2017-04-01 – 2019-03-31
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| Keywords | superlattice / quantum dots / perovskite / nanocrystal / charge migration / photoluminescence |
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| Outline of Annual Research Achievements |
This project focuses on the preparation of superlattices of semiconductor quantum dots and perovskite nanocrystals, which was followed by controlling density of photo-activated excitons by tuning the intensity of incident laser beam. Under low laser flounce, the photo -generated charge carriers were stabilized in the superlattice structures, providing carriers with microsecond lifetimes. However, in highly-excited superlattices, the lifetime was decreased to the nanosecond scale. Furthermore, the intensity of emitted photons increased exponentially with increase in the incident photon flux, suggesting that the highly-excited superlattices follow radiative relaxation. However, amplified stimulated emission was not detected, which can be due to random diffusion of charges in the film. Overall, this research validated the breaking of 1 nanocrystal, 1 photon, 1 exciton relation by controlling the excitation intensity dependent multiplication, pooling and diffusion of charge carriers.
This research expands to evaluate the roles of material composition, electron/hole defects, and the intensity and energy of excitation light on the diffusion and recombination of multiple charges in superlattices.
Unique outcomes of this research are twofold: (i) stable, long-lived charge carriers are generated by preparing self-assembled nanocrystal films of quantum dots and perovskites, and (ii) accomplished optical control of charge carrier density and their mode of recombination in nanocrystal assemblies.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
Research activities are all precisely focused in the direction that was proposed initially. The results obtained are all satisfactory. Young researchers such as doctor course students are attracted to this research. To-date three PhD students work on this project, preparing novel 2D and 3D materials based on quantum dots and perovskites and piling up new, in-depth information about photo-induced dynamics of charge carriers in such materials. Furthermore, three new students approached me personally to join the research activities related to this project, showing that the outcome seeds new research themes in the perovskite/quantum dot based photophysics, with continued support from JSPS. Also, one doctor course student from Indian Institute of Science Education had joined this project as a visiting student, which was directly supported by the program leader, Prof. Hiroshi Miyasaka. In addition to the above members, one doctor course student from Indian Institute of Technology Hyderabad expressed interest in joining the lab and work on problems closely related to the project.
Collaborative research with this area continues with Prof. Tsukasa Torimoto of Nagoya University (Group A01) and Prof. Martin Vacha of Tokyo Institute of Technology (Group A03). My expectation is that the outcome of the research would extensively exceed than what was initially expected.
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| Strategy for Future Research Activity |
One of the important remaining challenges in this project is extraction of evidence about the mechanism of long-range charge carrier migration in self-assembled nanocrystal films, which will be investigated in the remaining period. Also, it is essential to prove how carrier-carrier interactions in highly-excited superlattices lead to an exponential increase in the rate of radiative recombination. For these purposes, superlattices of nanocrystals with different band-gap materials will be prepared by controlling their assembly and order of arrangements. In such materials, the migration of charge carriers will be carried out through different energy states. Spectrally and temporally resolved photoluminescence measurements will be carried out to characterize the dynamics of diffusion and recombination of charge carriers in highly-excited superlattices. Also, spatially and temporally controlled experiments will be conducted to validate the relations among excitation, and exciton migration and recombination. Furthermore, transient absorption measurements will be carried out to understand the interactions of charge carriers with phonons while migrating from nanocrystals to nanocrystals.
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Research Products
(18 results)
