Addressing optical dynamics in CdS quantum dots through composition regulation strategy

Colloidal quantum dots (QDs) have received intensive attention over the past few decades because of their size-dependent properties, which enable them to be used in various applications such as displays, light-emitting diodes, and solar cells. Controlling the synthesis conditions to produce QDs with the desired size and distribution is becoming an exciting area of focused research. In addition, surface passivation of QDs is critical to increase their photoluminescence (PL) quantum yield. Because of their higher surface-area-to-volume ratio, nanocrystals contain abundant surface defects that can be reduced by the presence of excess cations. In this work, CdS QDs with different Cd:S ratios (1:1, 2:1, 3:1, and 4:1) are synthesized by the hot-injection method. Absorption and PL spectra show that the optical peaks at the beginning of growth are shifted to the shorter wavelength region with increasing Cd concentration. In particular, the sizes, size distributions, relative PL intensities, and optical bandgap properties of the synthesized QD samples are characterized to demonstrate the effect of the cation–anion ratio on the optical properties of CdS QDs.