Abstract
Over recent years, quantum dots (QDs) based on ternary metal dichalcogenides have attracted a lot of attention due to their unique properties and a range of potential applications. Here, we review the latest studies on the optical properties of AgInS2/ZnS QDs with emphasis on their theoretical modeling, and present our investigations of electronic transitions invisible in unstructured absorption spectra of AgInS2/ZnS QDs. The analysis of the absorption, photoluminescence excitation (PLE), and magnetic circular dichroism (MCD) spectra of hydrophobic and hydrophilic AgInS2/ZnS QDs of different sizes enables us to determine positions of electron transitions in these QDs. We demonstrate that the use of the second derivative of PLE spectra provides more unequivocal data on the position of the energy transitions compared with the second derivative of absorption spectra. Analysis of the MCD spectra reveals that the magnetic field induces energy level mixing in AgInS2/ZnS QDs in contrast to the traditional Cd-based QDs, where MCD is associated only with removing degeneracy of the excited energy level.
Highlights
Quantum dots (QDs) of ternary metal dichalcogenides (CuInS2 and AgInS2 ) are considered promising alternatives to binary cadmium and lead-containing chalcogenide quantum dots (QDs)
To reduce machine artifacts in magnetic circular dichroism (MCD) spectra that originated from baseline imperfections, we treated MCD spectra as follows: (i) calculated a correction spectrum as a half of the sum of MCD spectra recorded under magnetic field of an opposite sign and (ii) subtracted the obtained correction spectrum from the original MCD spectra
0.2–0.3 eV, which is much smaller than demonstrated that by using spectra, we can gain more detailed information on electronic the typical Stock shifts reported for AIS/ZnS QDs of 0.4–0.8 eV [18,43,44,52]
Summary
Quantum dots (QDs) of ternary metal dichalcogenides (CuInS2 and AgInS2 ) are considered promising alternatives to binary cadmium and lead-containing chalcogenide QDs. The main feature of ternary QDs is their high tolerance to defect states, which leads to the formation of broadband absorption and emission. The Ag 4d10 orbital is lower in energy than the Cu 3d10 orbital and, as a result, AgI atoms can have both 6- and 4-coordination, while CuI atoms energetically favour 4-fold coordination [10]. This makes the structure of AgInS2 QDs more tolerant to the formation of defect states and provides additional opportunities for the tuning of their optical properties [11]
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