Proceedings of MATSUS Spring 2025 Conference (MATSUSSpring25)
DOI: https://doi.org/10.29363/nanoge.matsusspring.2025.195
Publication date: 16th December 2024
Colloidal nanocrystals (NCs) are a very promising class of materials when it comes to the search for cheap and efficient light sources. Environmentally safer ternary quantum dots from I-III-VI class, such as AgInS2, or CuInS2, or quaternary alloys like Ag-In-Zn-S have not been studied as much as toxic Cd and PB chalcogenides. In order to understand the intrinsic optical properties, including the mechanism of light emission by alloyed quaternary Ag-In-Zn-S quantum dots, we performed spectroscopic studies of single NCs. We measured the dynamics of the emission spectra of ~40 spherical single quantum dots with an average diameter of 6.2 nm. There is a significant difference in the emission linewidth between the colloidal solution (425 meV) and the single NCs (250 meV on average). In order to examine whether spectral diffusion occurs, we studied statistics on the correlations between the parameters of the emission spectra. A significant amount (~50%) of NCs show a negative correlation (Pearson correlation coefficient ρ between -0.25 and -0.8) between energy and the linewidth. This supports the theory of moving surface charge inducing electric field causing the quantum-confined Stark effect. Moreover, it is a solid fingerprint of spectral diffusion. Almost all (95%) NCs show a negative correlation between emission peak amplitude and width with ρ between -0.25 and -0.85. We also observe a positive correlation between energy and emission intensity for almost 50% of NCs with ρ between 0.2 and 0.75. This observation is important in the discussion on the emission mechanism from these structures, considering between Donor-Acceptor Pair and Free-To-Bound mechanisms, as the occurrence of this correlation points to the Free-To-Bound recombination mechanism. These results are compared with smaller NCs with a diameter of 3.7 nm. The observed even stronger correlations confirm the validity of the surface charge theory, since for smaller QDs we would expect stronger induced electric fields.
This work was supported by National Science Centre Poland projects no. UMO-2019/35/B/ST3/042335, 2019/35/B/ST3/03426 and 2018/31/G/ST3/03596.
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