DOI: https://doi.org/10.29363/nanoge.incnc.2021.042
Publication date: 8th June 2021
Natural high carrier concentration and electron occupancy in the conduction band are remarkable properties of self-doped colloidal quantum dots (CQDs). It has been revealed that the silver chalcogenides and mercury chalcogenides CQDs have intraband transitions that are induced by the nature of self-doped CQDs. The self-doping property promotes the intraband transition but forbids the interband transition of the material. Thus, the self-doped CQDs are an applicable material that could carefully probe the electronic dynamics and energy structure in nanocrystals. Further understanding of the intraband transitions can extend the nanocrystal application.
The Ag2Se CQDs is a fascinating MWIR active material that has a high potential for future application. The Ag2Se CQDs intraband transition is reported for the first time by Prof. Jeong’s group in ACS photonics. A spectro-electro-chemistry (SEC) method has disclosed the intraband transition of Ag2Se CQDs and proves that the interband transition of Ag2Se CQDs exists at higher energy. Interestingly, the silver selenide CQDs have revealed a broken degeneracy of the p-state. The Ag2Se CQDs undergo the crystal structural transformation from cubic to tetragonal nanocrystal structure with increasing size. Accordingly, the corresponding degeneracy broken of the 1Pe 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. Considering that the unsophisticated intraband transitions of self-doped CQDs can be achieved from the HgS CQDs. Thus, the HgS conduction band was thoroughly investigated with MWIR pump-probe spectroscopy. The pico-second time decay shows three decaying components: exciton lifetime, Auger recombination, and, interestingly, electron-vibration energy transfer (EVET) to surface ligands. The HgS decay shows unexpectedly fast Auger component ~ 1 ps and slow EVET process ~ 500 ps. The intraband transition study could elucidate the challenging observations such as blinking of QDs, excessive charging in QDs device, and hot electron dynamics in conduction band coupled to nanocrystals’ surface states.
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