Figure 2: PbS QDs produced at different water-bath temperatures.

TEM images of samples produced by laser irradiation for 20 min at a, 20 °C and c, 0 °C. Scale bars, 20 nm. Size histograms of QDs prepared at b, 20 °C and d, 0 °C, and corresponding Gaussian fits. (e) Normalized room-temperature photoluminescence spectra of PbS QDs with respective diameters d, with an excitation wavelength of 400 nm. The discernable feature around 1,400 nm (0.9 eV) of the dashed curve could be attributed to the absorption by atmospheric water vapor¹⁴.