Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound semiconducting quantum dots. Various methods for synthesizing these quantum dots are discussed, as well as their resulting properties. Quantum states and confinement of their excitons may shift their optical absorption and emission energies. Such effects are important for tuning their luminescence stimulated by photons (photoluminescence) or electric field (electroluminescence). In this article, decoupling of quantum effects on excitation and emission are described, along with the use of quantum dots as sensitizers in phosphors. In addition, we reviewed the multimodal applications of quantum dots, including in electroluminescence device, solar cell and biological imaging.

https://www.mdpi.com/1996-1944/3/4/2260/pdf

Quantum Dots and Their Multimodal Applications: A Review

This work explores the sensitization of luminescent lanthanide Tb3+ and Eu3+ cations by electronic structure of zinc sulfide (ZnS) semiconductor nanoparticles. Excitation spectra collected while monitoring the lanthanide emission bands reveal that the ZnS nanoparticles act as an antenna for the sensitization of Tb3+ and Eu3+. The mechanism of lanthanide ion luminescence sensitization is rationalized in terms of an energy and charge transfer between trap sites and is based on a semiempirical model, proposed by Dorenbos and co-workers (Dorenbos, P. J. Phys.: Condens Matter 2003, 15, 8417-8434; J. Lumin. 2004, 108, 301-305; J. Lumin. 2005, 111, 89-104. Dorenbos, P.; van der Kolk, E. Appl. Phys. Lett. 2006, 89, 061122-1-061122-3; Opt. Mater. 2008, 30, 1052-1057. Dorenbos, P. J. Alloys Compd. 2009, 488, 568-573; references 1-6.) to describe the energy level scheme. This model implies that the mechanisms of luminescence sensitization of Tb3+ and Eu3+ in ZnS nanoparticles are different; namely, Tb3+ acts as a hole trap, whereas Eu3+ acts as an electron trap. Further testing of this model is made by extending the studies from ZnS nanoparticles to other II-VI semiconductor materials; namely, CdSe, CdS, and ZnSe.

/pdf/lanthanide-sensitization-in-ii-vi-semiconductor-materials-a-3d251dtngv.pdf

Lanthanide Sensitization in II−VI Semiconductor Materials: A Case Study with Terbium(III) and Europium(III) in Zinc Sulfide Nanoparticles

Effect of Al doping on the structural, optical and photoluminescence properties of ZnS nanoparticles

Controlling the exciton energy of zinc oxide (ZnO) quantum dots by changing the confinement conditions.

An emerging class of heterostructures with unprecedented (photo)electrocatalytic behavior, involving the combination of fullerenes and low-dimensional (LD) nanohybrids, is currently expanding the field of energy materials. The unique physical and chemical properties of fullerenes have offered new opportunities to tailor both the electronic structures and the catalytic activities of the nanohybrid structures. Here, we comprehensively review the synthetic approaches to prepare fullerene-based hybrids with LD (0D, 1D, and 2D) materials in addition to their resulting structural and catalytic properties. Recent advances in the design of fullerene-based LD nanomaterials for (photo)electrocatalytic applications are emphasized. The fundamental relationship between the electronic structures and the catalytic functions of the heterostructures, including the role of the fullerenes, is addressed to provide an in-depth understanding of these emerging materials at the molecular level.

Fullerenes as Key Components for Low-Dimensional (Photo)electrocatalytic Nanohybrid Materials

Influence of annealing temperature on the photoluminescence properties of ZnO quantum dots

Cu 2+ -doped ZnS quantum dots were synthesized by a chemical precipitation method in water/ethanol solution. The quantum dots obtained were characterized by X-ray diffraction, transmission electron microscopy and spectroscopy techniques including X-ray photoelectron spectroscopy. The [S 2- ]/ [Zn 2+ ] ratios have an effect on the photoluminescence of both aqueous solutions and powders of Cu 2+ -doped ZnS quantum dots. For aqueous samples, a green luminescence centre is observed in the spectrum of sample 1 with [S 2- ]/[Zn 2 +] = 1:2 and a blue one for sample 2 with [S 2- ]/[Zn 2+ ] = 1:1. For powders, only the green emission is the main luminescence centre, and the integrated intensity in the blue emission region of sample 1 is stronger than that of sample 2. Compared with the spectrum of CuS powders, the X-ray-induced Auger electron spectrum of Cu L 3 M 45 M 45 in ZnS quantum dots shows a unique spectral characteristic. The 3d level of the Cu 2+ ion is split into two different energy levels at 334.0 and 347.2 eV, respectively.

Photoluminescence and XPS investigations of Cu2+-doped ZnS quantum dots capped with polyvinylpyrrolidone

The Eu3+-doped ZnS nanocrystals prepared by the chemical method have a cubic structure. All the transitions 5D0 ? 7FJ (J = 0, 1, 2, 3, 4, 5, 6) of Eu3+ were observed in ZnS nanocrystals. In particular, the forbidden transitions of 5D0 ? 7F0, 5D0 ? 7F3 and 5D0 ? 7F5 were all observed and their observed values of energies were found to match well with those predicted from a complete diagonalization of the crystal-field Hamiltonian for Eu3+. The photoluminescence of the transition 5D0 ? 7F1 confirms the crystal-field analysis that in the first order approximation the crystal field has no effect on the multiplet 7F1. The crystal-field analysis shows that the multiplet 7F2 has a doubly degenerate sublevel and a triply degenerate sublevel, which also agrees with the photoluminescence results very well. Although not all sublevels of crystal levels of multiplet 7F4 were observed in the photoluminescence of the transition 5D0 ? 7F4, the crystal-field parameter was estimated from the width of the emission band of this transition. In accordance with the superposition model, the crystal-field parameters and were fitted to be ?59.8?meV and 41.6?meV, respectively.

Photoluminescence properties of the Eu3+-doped ZnS nanocrystals and the crystal-field analysis

The invention relates to a preparation method of CdS quantum dot with adjustable size, belonging to technical field of the preparation of CdS quantum dot. The A solution is formed by mixing the cadmium chloride, the ammonium chloride and water in set matching and the B solution is formed by mixing the mercaptoethanol, the thiourea and water in set matching. The A solution and the B solution are mixed at the temperature a little higher than the ambient temperature and then carried on the synthetic reaction, and then the CdS quantum dot can be obtained. The preparation method of CdS quantum dot with adjustable size has the advantages that the size of the quantum dot of the product can be adjusted by controlling the quantity of the mercaptoethanol.

Preparation method of size-adjustable cds quantum dot

Zinc sulﬁde semiconductor nanocrystals doped with Yb 3+ ions have been prepared through a chemical precipitation method using PVP (polyvinylpyrrolidone) as a capping agent. The structure of the nanoparticles has been analyzed by X-ray diffraction (XRD). The average size of the nanoparticles is found to be 3.7±0.4 nm. Photoluminescence spectra were recorded for doped ZnS nanoparticles as a function of temperature between 9 and 300 K. The results suggest that two emission bands have been observed at different temperatures. The width of 1.269 eV peak increases as temperature is raised. A shift of lower energy emission band has been observed with the change of temperature. Moreover, the magnetic measurement showed that the sample exhibits paramagnetic behavior.

Temperature dependence of photoluminescence and magnetic properties in Yb3+-doped ZnS nanocrystals

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