Preparation of Monodisperse CdS Nanocrystals by Size Selective Photocorrosion

Abstract

Narrowing the size distribution of polydisperse CdS nanocrystals whose average diameter was 42 Å and standard deviation was 19 Å was achieved utilizing size selective photocorrosion with sequential irradiation with monochromatic light whose wavelength was changed step by step from 490 to 430 nm in air-saturated sodium hexametaphosphate solution. With decreasing the wavelength of irradiated light, the first exciton peak was gradually developed in the absorption spectrum of the resulting CdS colloid, and the nearly monodisperse CdS nanocrystals of 22 Å were finally obtained, which were thought to be the smallest particles that were present in the original CdS colloid. Analyses of the amount of sulfate ions produced by photocorrosion of Q-CdS colloids revealed that the number of Q-CdS particles in the colloid decreased with promotion of photocorrosion, suggesting that during the course of photocorrosion photocorroded CdS particles were agglomerated to give larger particles which were further photocorroded. The molar absorption coefficient of CdS particles at the first exciton peak was found to be independent of the particle size.

Layer-by-layer accumulation of cadmium sulfide core—silica shell nanoparticles and size-selective photoetching to make adjustable void space between core and shell

“…When the technique was applied to CdS, the particle size could be controlled within the range of 3.5 to 1.7 nm simply by selecting the wavelength of monochromatic irradiation light in the range of 488 to 365 nm [42][43][44][45][46][47]. Recently we have also applied this technique successfully to control core size in silica-coated CdS nanoparticles, i.e., a CdS core-silica shell structure.…”

Analytical Applications of Enzymatic Growth of Quantum Dots

“…From the UV/Vis spectrum we observe increased absorption below 480 nm, and a shoulder at about 380 nm. The presence of this shoulder is explained by 1S h -1S e excitonic transition [22] characteristic of nanoparticles with a diameter of~2-3 nm, according to the work of Peng et al [23] From the emission spectrum of enzymatically generated CdS QDs we observe a maximum at 600 nm and a lower peak at 440 nm, which arises from excitonic emission of CdS nanoparticles. [24] The size of CdS nanoparticles was determined by high resolution transmission electron microscopy (TEM).…”

Nanostructure Engineering of Size-Quantized Semiconductor Particles for Photoelectrochemical Applications

“…The size distribution of the photoetched particles was much narrower than that of the original particles, the standard deviation of size distribution being less than 10% of the average diameter. The sizeselective photoetching technique has been widely used to control the size of quantized nanoparticles such as ZnO, 29 ZnS, 30 CdS, 26,27,31 CdSe, 32 CdTe, 33 InP, 34 InGaN, 35 and AgInS 2 nanoparticles. 21 However, being different from the case of photoetching CdS particles, an additional complexing agent such as NH 3 was necessary to successfully complete size-selective photoetching of AgInS 2 nanoparticles, because Ag + ions released along with the photoetching formed an insoluble Ag 2 O passivation layer on the particle surface to prevent further photoetching of AgInS 2 .…”