Project's information

Project's title Study of Carrier dynamics in Cadmium (Cd)-containing heterogeneous quantum dots
Project’s code GUST.STS.ĐT2019-KHVL03
Research hosting institution Graduate University of Science and Technology
Project leader’s name Ph.D. Man Minh Tan
Project duration 01/06/2019 - 30/06/2022
Project’s budget 3000 million VND
Classify Excellent
Goal and objectives of the project

The project aims to study investigate carrier dynamics in Cd-based heterogeneous structures (i.e., CdTe/ZnTe, CdSe/CdS, CdSe/ZnS) including (1) redistribution of excitation energy, (2) carrier‐carrier and carrier‐phonon scattering, (3) Band filling and dynamic Burstein–Moss shift; and (4) carrier multiplication (CM) and Auger recombination.

Main results

The hot-pump method has been used to effectively produce CdSe quantum dots. Reaction time and morphology are correlated. According to the results, the band gap energy of CdSe QDs decreases with decreasing size, with the rule being the most significant factor. It's remarkable how well the optical spectral energy gap calculation findings and the HRTEM photos match up. Energy levels of the first to fourth optical transitions between electron states (1Se and 1Pe) and hole states (s- and p-symmetry) fall rapidly with increasing CdSe QDs' size.
The colloidal CdSxSe1-x ternary nanoalloys were synthesized by the hot inject technique and the simple phosphine-free way. Band gaps may be adjusted from 2.81 to 1.95 eV by increasing Se content. The effect of lattice strain on CdSexS1-x carrier dynamics was investigated. Lactice strains occur in CdSexS1-x nanoalloys due to component mismatches. The multiexponential decay function revealed that the average lifetime decreases with increasing Se content. These rates are connected to the lattice strain in nanoalloys.
Based on the CdTe/ZnTe quantum dots (QDs), which are fabricated using molecular beam epitaxy (MBE) methods, we have developed a model that allows explaining the unusual temperature dependence of the full width at half maximum (FWHM) of photoluminescence (PL) at low excitation power, which have considered by the following recombination channels: (1) discrete recombination between electrons and holes in an s or in a p orbital, correspond to 1S[1S3/2(h)-1Se], 2S[2S3/2(h)-1Se], and 1P[1P3/2(h)-1Pe] transitions; (2) when the electron continuum states start to be populated, the nonradiative processes become predominant so that type thermal escape of carriers, which assisted by the carrier scattering via optical phonons.

Novelty and actuality and scientific meaningfulness of the results

- The results of the project solved some research problems on Cd-containing quantum dots, influences of size, shape, and ligands on the optical properties, optical transitions and carrier dynamics. And open application oriented research on these Cd-containing QDs in the future.
- The project contributes to promote collaboration between research units; contributes to human resource training for science and technology.

Products of the project

- Scientific papers in referred journals (list): 03
[1]. Lê Anh Thi, Nguyễn Minh Hoa, Đỗ Thị Anh Thư, Nguyễn Tiến Đại, Phan Ngọc Hồng, Mẫn Minh Tân, Sự phụ thuộc vào kích thước của độ rộng khe năng lượng và thời gian sống của các chấm lượng tử CdSe, Tuyển tập báo cáo tại Hội nghị Vật lý Chất rắn và Khoa học Vật liệu Toàn quốc – SPMS 2019, Tp. Quy Nhơn, Bình Định, 02-04/11/2019, pp.277-280.
[2]. Đỗ Thị Anh Thư, Phan Ngọc Hồng, Lê Duy Mạnh, Lê Anh Thi, Mẫn Minh Tân, Absorption properties and Quantum Confinement of colloidal CdSe quantumdots., Vietnam Journal of Catalysis and Adsorption, 10 –special issue 1 (2021) 117-120.
[3]. Sung Hun Kim, Taeho Shin, Minh Tan Man, Hong Seok Lee, Size‑dependent energy spacing and surface defects of CdSe quantumdots in strong confnement regime, Applied Nanoscience (2022);  (ISI).
- Technological products (describe in details: technical characteristics, place):
The cadmium -containing quantum dots: 02 samples.
•    Packaging: 100 mL in glass bottle
•    Store at room temperature (4-25 °C)
•    Stabilizing ligand: Octadecylamine  
•    Particle sizes: 2.0-6.9 nm
•    Absorption peaks: 460-640 nm
•    Emission peaks: 460-670 nm

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