Nature of luminescence of PbS quantum dots synthesized in a Langmuir–Blodgett matrix

The luminescence and structural properties of PbS quantum dots in a Langmuir–Blodgett matrix and after the removal of this matrix have been studied. It has been found that the photoluminescence peak of quantum dots in the matrix is near 1.6 eV, and luminescence disappears after the removal of the matrix. Beyond the matrix, quantum dots begin to luminesce at an energy of 0.8 eV only after aging in air lasting many days, which can be attributed to the passivation of surface defects because of oxidation. The size distribution of quantum dots in the initial Langmuir–Blodgett matrix and after its removal has been determined by transmission microscopy. Using the size distribution of quantum dots, the photoluminescence spectra have been calculated for quantum dots with different shells—Langmuir–Blodgett matrix/alkanes or oxide. It has been established that the shift of the photoluminescence spectrum of quantum dots toward lower energies is due to a decrease in the height of barriers and to an increase in the sizes of quantum dots.