The highly luminescent CdSe/CdS/ZnS core–multi-shell quantum dots (QDs) were prepared without a protective atmosphere through the precursor injection method (phosphine free) in paraffin liquid and ...

Effect of Polymer Capping on Photonic Multi-Core–Shell Quantum Dots CdSe/CdS/ZnS: Impact of Sunlight and Antibacterial Activity

Luminescent Manganese/Europium doped ZnS quantum dots: Tunable emission and their application as fluorescent sensor

Study of photoluminescent and photometric properties of ZnS:Mn2+ quantum dots for white light emission

Optoelectronics and optical filter applications require wide bandgap semiconductors as photo-anode and surface passivation layers in sensitized solar cells and biomedical and biosensors fields such as optical filters [1–4]. Selecting suitable wide bandgap semiconductors increases the valuable implementation of desired devices. However, bulk semiconductors harvest only a particular spectrum, QDs help in harvesting large radiation spectra because of the tunable bandgap. Also, aqueous-based methods are eco-friendly, economical, biocompatible, and non-toxic. Therefore, in this study, ZnS quantum dots (QDs) were synthesized at 9.5 pH and 70 ͦ C temperature using an aqueous-based chemical route method. A comparative study was presented using hydrazine hydrate and ammonium chloride as reducing agents for Zinc precursor and 3-mercaptopropionic acid (MPA) as capping agents. Confinement was achieved in ZnS using MPA as a stabilizer. Optical properties were studied using a photoluminescence (PL) spectrophotometer where photoluminescence (PL) shows emission behavior and photoluminescence excitation (PLE) shows excitation behavior of ZnS. Emission peaks were observed at 386 nm in as-prepared ZnS NPs and at 316 nm in confined QDs. Sharp band edge luminescence and the possibility to confine ZnS NPs show its eligibility in optoelectronics and optical filters in biological applications.

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Optical Properties of ZnS Quantum Dots: Applications in Solar cells and Biomedicine

In this research, the surface capped pure ZnS nanoparticles, as well as the Cd- and Hg-doped ones were synthesized via a green ultrasonic-assisted co-precipitation route. The products were characterized by X-ray diffraction, scanning and transmission electron microscopies, Fourier transform infrared, UV–Vis and photoluminescence spectroscopies. The results showed that the synthesized spherical-like nanoparticles are single-phased and well-dispersed with diameters of about 3 nm. They were crystallized in a cubic zincblende structure whose lattice constants increase on doping due to the larger ionic radii of the dopants. The Cd/Hg substitution results in slightly less microstrain and so rather smaller particles. The studied nanoparticles are direct band gap materials whose band gap values vary with Cd/Hg doping from 4.31 eV for ZnS to 3.94/4.40 eV as a result of the competition between the quantum size effect and the composition effect. The effect of the isoelectronic Cd and Hg doping is also revealed as the weakening of the blue photoluminescence band around 430 nm originated from the defect states in ZnS matrix, and the appearance of a red excitonic emission at 640 nm. It was found that in these nanoparticles being smaller than Bohr dimension, the particle size is a determinative parameter for governing the efficiency of the radiative emissions.

A comparative study of the isoelectronic Cd and Hg substitution in EDTA-capped ZnS nanocrystals

In this study, a chemical method was used to synthesise ZnS quantum dots (QDs) with low cost and simple process. A fixed molar ratio 1:1 of zinc chloride and sodium sulfide has been used for preparing two samples A and B. The X-ray diffraction (XRD) analyses prove the cubic phase of ZnS with an average particles size of (3-29) nm According to UV-Vis. spectra analyses, a large blue shift over 32 and 48 nm was observed, while the band gaps energy (Eg) were 3.55 and 3.8 eV for A and B samples respectively. The emission spectrum of quantum dots carries more evidence on the presence of shallow at 373 and 367 nm originated from the interstitial Zn and traps at 428 and 439 nm, whose origin ascribed to defects zinc vacancy (VZn), while 541 nm was due to sulfide vacancy (VS). QDs-LED hybrid devices were fabricated using ITO/PEDOT: PSS/Poly-TPD/ZnS-QDs/layers with two types of cathode materials LiF and Al. Using LiF as cathode in addition to the Al gives good enhancement to light generation in compares with that of Al cathode only. The spectra 350-700 nm appeared a wide emission band according to the EL measurement.

https://iopscience.iop.org/article/10.1088/1742-6596/1032/1/012010/pdf

Wasan R. Salah

Papers

Synthesis of ZnS Quantum Dots for QDs-LED hybrid device with different cathode materials