Optical Properties Of CdS Quantum Dots Research Articles

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.

Synthesis of Pb-doped CdS quantum dot using SILAR method on mesoporous TiO2 layer

This research focuses on the fabrication of CdS quantum dot-sensitized solar cells (QDSCs). CdS quantum dots (QDs) were fabricated on a mesoporous TiO2 electrode using a successive ion layer adsorption and reaction (SILAR) method and Pb doping concentrations (0, 2, 4, 10, 15, 20, 25 and 30 %mol) were varied. The change in optical properties of CdS QDs was found to be affected by Pb doping. The Pb-doped CdS QDSCs were determined under the illumination of 100 mWcm−2, which indicated the highest power conversion efficiency (PCE) was 1.73% at 20% Pb dopant.

Synthesis of CdS QDs with single cubic and hexagonal lattice for blue-light-blocking nanocomposite films with a narrow absorbing transitional band

It is highly expected to develop blue-light-blocking filters with narrow absorbing transitional band, so as to filter out only harmful blue light below 455 nm. In this paper, CdS quantum dots (QDs) with single cubic and hexagonal lattice were synthesized by a solvothermal method using mercaptoethanol as capping agent. The results show that hexagonal-type CdS QDs with a diameter about 2.5 nm was synthesized after 10 min of reaction, and then grow slowly up at low temperature (80 °C). Higher temperature (160 °C) helps to synthesize cubic-type CdS that grows rapidly to a final size about 4 nm. Hexagonal and cubic CdS all show separated energy level structure corresponding to a band gap of 3.59 eV and 3.1 eV, respectively. CdS QDs were compounded into poly(N,N-dimethacrylamide) matrices to prepare transparent nanocomposite films, in which the optical properties of CdS QDs can be preserved, and the nanocomposite films, especially ones with 30 wt% of cubic CdS, shows a narrow blue-light-absorbing transitional band. The wavelength span from 5 % to 80 % of maximum transmittance is only 20 nm (440−460 nm), indicating a potential application in ocular protection by sealing it between two layers of glass panels as blue-light-blocking filter due to its sharp cut on/off and wavelength-dependent blue transmittance.

Cadmium sulfide quantum dots stabilized by castor oil and ricinoleic acid

Castor oil and ricinoleic acid (an isolate of castor oil) are environmentally friendly bio-based organic surfactants that have been used as capping agents to prepare nearly spherical cadmium sulfide quantum dots (QDs) at 230, 250 and 280°C. The prepared quantum dots were characterized by Ultra violet–visible (UV–vis), Photoluminescence (PL), Transmission Electron Microscopy (TEM), High Resolution Transmission Electron Microscopy (HRTEM) and X-ray diffraction (XRD) giving an overall CdS QDs average size of 5.14±0.39nm. The broad XRD pattern and crystal lattice fringes in the HRTEM images showed a hexagonal phase composition of the CdS QDs. The calculated/estimated average size of the prepared castor oil capped CdS QDs for various techniques were 4.64nm (TEM), 4.65nm (EMA), 5.35nm (UV–vis) and 6.46nm (XRD). For ricinoleic acid capped CdS QDs, the average sizes were 5.56nm (TEM), 4.78nm (EMA), 5.52nm (UV–vis) and 8.21nm (XRD). Optical properties of CdS QDs showed a change of band gap energy from its bulk band gap of 2.42–2.82eV due to quantum size confinement effect for temperature range of 230–280°C. Similarly, a blue shift was observed in the photoluminescence spectra. Scanning electron microscope (SEM) observations show that the as-synthesized CdS QDs structures are spherical in shape. Fourier transform infra-red (FTIR) studies confirms the formation of castor oil and ricinoleic acid capped CdS QDs.