Optical and Structural Change in Self-Doping Quantum Dots

Dongsun Choi^a, Juhee Son^a, Mihyeon Park^a, Juyeon Jeong^a, Bitna Yoon^a, Kwang Seob Jeong^a

^aKorea University, Department of Chemistry, College of Science, 145 Anam-ro, Anam-dong, Seongbuk-gu, Seoul, Corea del Sur, Seoul, Korea, Republic of

Proceedings of Internet Conference for Quantum Dots (iCQD)

Online, Spain, 2020 July 14th - 17th

Organizers: Quinten Akkerman, Raffaella Buonsanti, Zeger Hens and Maksym Kovalenko

Poster, Dongsun Choi, 074
Publication date: 3rd July 2020

ePoster:

Electron occupation in a few states of the conduction band (CB) with high carrier density is a natural character of self-doped colloidal quantum dots (CQDs). The electronic occupation in the CB forbids the conventional bandgap transition of CQDs and allows higher quantized electronic transitions known as intraband transitions. It has been revealed that the silver chalcogenides and mercury chalcogenides CQDs could show intraband transitions that are induced by the nature of self-doped CQDs. Due to the electron occupation in the CB, the self-doped CQDs can expand from semiconductor to semi-metal nanocrystal by synthetic self-doping control. In this poster, I will present the optical and structural change of the self-doped mercury chalcogenides and silver chalcogenides CQDs.

The steady-state intraband transitions are carefully investigated with synthetic control to understand the metallic phase transition properties in self-doped CQDs; 1) size, 2) cation exchange and 3) structural dependency. First, a singly and doubly occupied quantum state (SOQS and DOQS) in HgSe CQDs is achieved with varying the size of the CQDs which affects the carrier density. The electron paramagnetic resonance spectrum indeed confirms the single electron occupation of 1Se state in the self-doped HgSe CQDs. Second, the Cd_1-xHg_xSe alloy exhibits a phase transition to the metal with increasing mercury cation portion in the alloy CQDs. Interestingly, the intraband transition of the alloy CQDs are simultaneously transformed into the localized surface plasmon resonance (LSPR) in the mid-infrared region as the metallic character develops. Lastly, the Ag₂Se CQDs undergoes the crystal structural transformation from cubic to tetragonal nanocrystal structure with increasing the size. Accordingly, the corresponding degeneracy broken of the 1P_e states is optically observed along with the structural transformation. Strikingly, the Ag₂Se CQDs plasmonic character coexists with the steady-state intraband electronic transition, which indicates the quantum-plasmon characters in the self-doped Ag₂Se CQDs.

References:

[1] Jeong, J., Yoon, B., Kwon, Y. W., Choi, D. & Jeong, K. S. Singly and Doubly Occupied Higher Quantum States in Nanocrystals. Nano Lett. 17, 1187–1193 (2017).

[2] Choi, D. et al. Major electronic transition shift from bandgap to localized surface plasmon resonance in CdxHg1-xSe Alloy Nanocrystals. Chem. Mater. 29, 8548–8554 (2017).

[3] Park, M., Choi, D., Choi, Y., Shin, H. B. & Jeong, K. S. Mid-Infrared Intraband Transition of Metal Excess Colloidal Ag2Se Nanocrystals. ACS Photonics 5, 1907–1911 (2018).

[4] Son, J., Choi, D., Park, M., Kim, J. & Jeong, K. S. Transformation of Colloidal Quantum Dot: From Intraband Transition to Localized Surface Plasmon Resonance. Nano Lett. 20, 4985–4992 (2020).

Acknowledgements:

This work is supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT, and Future Planning (NRF-2016R1C1B2013416, NRF2018R1D1A1A02085371, NRF-2019M3D1A1078299), the Ministry of Education (NRF20100020209), and a Korea University Grant (NRF2013R1A1A2062323).

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