Abstract
The mechanism features of colloidal quantum dots (QDs) passivation with thioglycolic acid molecules (TGA) for cases of different luminescent properties is considered using FTIR. This problem is considered based on FTIR spectra analysis for various ionic forms of TGA. Experimental TGA molecules FTIR spectra is interpreted, basing on the data on modeling of TGA vibrational modes, realized in the framework of density functional method (DFT /B3LYP/6-31+G(d)) taking into account the vibrations anharmonicity of every functional group. This approach provides a significant improvement in the agreement between the experimental and calculated data. FTIR spectra of AgS/TGA QDs with exciton and recombination luminescence are differ from each other and B “freeB” TGA molecules. The TGA peak (2559 cm) disappears in FTIR spectra of AgS/TGA QD samples. This fact indicates the interactions between TGA thiol group and dangling bonds of AgS nanocrystals. AgS QDs passivation with TGA molecules leads to emergence (COO) (1584 cm) and (COO) (1387 cm) peaks. It indicates TGA adsorption in ionic form. For AgS/TGA QDs with exciton luminescence we observed (a) significant low-frequency shift of (COO) peak from 1388 cm to 1359 cm and high-frequency shift of (COO) peak from 1567 cm to 1581 cm; (b) change in the ratio of intensities of (COO) and (COO) vibrations. This feature is caused by the change in the symmetry of TGA molecules due to passivation of AgS quantum dots.For AgS/TGA QDs with recombination luminescence, the insignificant high-frequency shift of 7–10 cm for (COO) at 1567 cm and low-frequency shift of 3–5 cm for (COO) at 1388 cm, probably caused by the interaction of thiol with AgS surface is observed. Using FTIR spectra, it was found that IR luminescence photodegradation is also accompanied by changes in the thioglycolic acid molecules, which capped AgS QDs. In the case of AgS QDs with exciton luminescence, the degradation process is non-reversible. It is accompanied by TGA photodegradation with the formation of -thiol-substituted acyl radical (S-CH-CO) TGA.
Highlights
The problem of obtaining functional nanomaterials based on semiconductor colloidal quantum dots (QDs) with specific luminescent properties is relevant, primarily for creating luminescent sensors for biology, medicine, chemistry, geology, etc. [1,2,3,4,5,6,7,8,9]
The molecule functional groups are selected with aim of the removing or minimizing the concentration of QDs surface dangling bonds due to interaction with them.This provide optimal luminescent properties of colloidal quantum dots
Colloidal Ag2 S/Thioglycolic acid (TGA) QDs were prepared by the aqueous synthesis technique [18,19]
Summary
The problem of obtaining functional nanomaterials based on semiconductor colloidal quantum dots (QDs) with specific luminescent properties is relevant, primarily for creating luminescent sensors for biology, medicine, chemistry, geology, etc. [1,2,3,4,5,6,7,8,9]. The problem of obtaining functional nanomaterials based on semiconductor colloidal quantum dots (QDs) with specific luminescent properties is relevant, primarily for creating luminescent sensors for biology, medicine, chemistry, geology, etc. The molecule functional groups are selected with aim of the removing or minimizing the concentration of QDs surface dangling bonds due to interaction with them.This provide optimal luminescent properties of colloidal quantum dots. TGA bifunctionality is a specific feature of these molecules, acting as QDs passivators [4,20,21,22] These molecules can interact with dangling bonds QD through both the thiol and carbonyl groups [6,7,8,13,21,22,23]. It should be taking into account that TGA in a solution is capable to self-association, as well as the formation of other polynuclear complex forms (sodium salt, anion and dianion, etc.) [7,15,24,25,26]
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