Abstract:
The vibrations anharmonism effect of the OH-groups of solvent molecules on the quantum yield and decay time of IR luminescence of aqueous solutions of colloidal lead sulfide quantum dots, passivated with 2-mercaptopropionic acid molecules (PbS/2-MPA QDs) is considered. It has been shown that the longwave shift of the overtone band of the solvent vibrational modes relative to the luminescence band of PbS/2-MPA QDs (950 nm) in the conditions of replacing the solvent from H$_2$O to D$_2$O leads to the increase in the quantum yield from 2% to 5% and increase in the luminescence decay time from 2.4 $\mu$s to 6.0 $\mu$s and decrease in the non-radiative recombination constant by 2.5 times. Numerical calculations of the overlap integral of the donor luminescence spectrum (PbS/2-MPA QD) with the acceptor extinction spectrum (overtones of OH vibrations) showed the Förster radius $R_0$ = 0.4 nm. This value evidences the adsorption of solvent molecules on the QD interfaces during them dissolving in it. In this case, the approximation of the luminescence decay curves of PbS/2-MPA QDs demonstrates the greatest agreement with experimental data when the luminescence decay law takes into account the statistical distribution of the number of OH-groups of solvent molecules relative to the QDs. The obtained data indicate the implementation of a dipole-dipole mechanism of non-radiative transfer of electronic excitation energy from PbS/2-MPA QDs to the overtones of solvent OH-vibrations, located in the environing volume of QDs.
Keywords:luminescence, quantum yield, luminescence decay time, non-radiative processes, quantum dot, lead sulfide.
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