Synthesis of Zn(1-x)Cd(x)S:Mn/ZnS quantum dots and their application to light-emitting diodes

Controllable Synthesis and Optical Properties of ZnS:Mn2+/ZnS/ZnS:Cu2+/ZnS Core/Multishell Quantum Dots toward Efficient White Light Emission

The ability to control dopants and defects, as well as the core/shell structures, of quantum dots (QDs) is an essential nanotechnology to modify and optimize their photoluminescence properties. Herein, the optimized ZnS:Mn²⁺/ZnS/ZnS:Cu²⁺/ZnS core/multishell QDs have been prepared, and their luminescence properties depending on the ratios of the starting materials and the injection temperature of an extra sulfur source were discussed; finally the white light can be possibly obtained by mixing the blue light (emission peak at 450 nm originating from Cu²⁺ dopants or emission peaks at 405 and 430 nm corresponding to a defect emission center) and orange light (emission peak at 585 nm from Mn²⁺ dopants). As a controlled synthesis comparison, the optimum core/shell structures and key synthesis parameters have been determined, and the quantum yield (QY) of the as-obtained ZnS:Mn²⁺/ZnS/ZnS:Cu²⁺/ZnS core/multishell white light emitting QDs without defect emission was determined to be 38%. The practical white light device prototype has been also fabricated and the CIE color coordinate of (0.32, 0.34) with a warm white light has been realized upon the excitation of the commercial 370 nm UV LED chip, which demonstrated potential application for micro/nano optical functional devices.

A benzoperylene probe self-assembled on polyethyleneimine/manganese doped ZnS quantum dots: a new nanocomposite for bright and tunable white light emission

A white light emitting benzoperylene probe-polyethyleneimine capped quantum dots nanocomposite has been synthesized for the first time.

The energy-down-shift effect of Cd(0.5)Zn(0.5)S-ZnS core-shell quantum dots on power-conversion-efficiency enhancement in silicon solar cells

We found that Cd0.5Zn0.5S-ZnS core (4.2 nm in diameter)-shell (1.2 nm in thickness) quantum dots (QDs) demonstrated a typical energy-down-shift (2.76-4.96 → 2.81 eV), which absorb ultra-violet (UV) light (250-450 nm in wavelength) and emit blue visible light (∼442 nm in wavelength). They showed the quantum yield of ∼80% and their coating on the SiNX film textured p-type silicon solar-cells enhanced the external-quantum-efficiency (EQE) of ∼30% at 300-450 nm in wavelength, thereby enhancing the short-circuit-current-density (JSC) of ∼2.23 mA cm(-2) and the power-conversion-efficiency (PCE) of ∼1.08% (relatively ∼6.04% increase compared with the reference without QDs for p-type silicon solar-cells). In particular, the PCE peaked at a specific coating thickness of the Cd0.5Zn0.5S-ZnS core-shell QD layer; i.e., the 1.08% PCE enhancement at the 8.8 nm thick QD layer.

One solvent, one pot and free capping ligands: Synthesis of alloyed multipod-branched Cd(x)Zn(1-)(x)S nanocrystals

The solvent ethanolamine with the assistance of cationic doping has been applied to synthesize alloyed multipod-branched Cd(x)Zn(1-)(x)S (0<x<1) nanocrystals through a simple solvothermal route. During the growth of the alloyed multipod-branched nanocrystals, for one thing, the cationic doping enlarges the energy difference between wurtzite and zinc-blende phases; for another thing, the -OH groups of ethanolamine favor the thorough alloying effects and the formation of the zinc-blende-structured seeds, while the -NH(2) groups facilitate the subsequent preferential growth of the wurtzite-phased arms. The composition x of the alloyed multipod-branched Cd(x)Zn(1-)(x)S nanocrystals can be facilely tuned by Cd/Zn initial molar ratios. Furthermore, the absorption edges (corresponding to optical band gaps E(g)) and the near-band-edge emission peaks are varied with the doping Cd(2+) content x. It is reasonable for us to believe that ethanolamine can also be employed to fabricate other alloyed multipod-branched nanocrystals such as CdS(x)Se(1-)(x), CdSe(x)Te(1-)(x) and CdS(x)Te(1-)(x).

Semiconductor-nanocrystals-based white light-emitting diodes

In response to the demands for energy and the concerns of global warming and climate change, energy efficient and environmentally friendly solid-state lighting, such as white light-emitting diodes (WLEDs), is considered to be the most promising and suitable light source. Because of their small size, high efficiency, and long lifetime, WLEDs based on colloidal semiconductor nanocrystals (or quantum dots) are emerging as a completely new technology platform for the development of flat-panel displays and solid-state lighting, exhibiting the potential to replace the conventionally used incandescent and fluorescent lamps. This replacement can cut the ever-increasing level of energy consumption, solve the problem of rapidly depleting fossil fuel reserves, and improve the quality of the global environment. In this review, the recent progress in semiconductor-nanocrystals-based WLEDs is highlighted, the different approaches for generating white light are compared, and the benefits and challenges of the solid-state lighting technology are discussed.

Reverse micelle-derived Cu-doped Zn(1-x)Cd(x)S quantum dots and their core/shell structure

Reverse micelle chemistry-derived Cu-doped Zn(1-x)Cd(x)S quantum dots (QDs) with the composition (x) of 0, 0.5, 1 are reported. The Cu emission was found to be dependent on the host composition of QDs. While a dim green/orange emission was observed from ZnS:Cu QDs, a relatively strong red emission could be obtained from CdS:Cu and Zn(0.5)Cd(0.5)S:Cu QDs. Luminescent properties of undoped QDs versus Cu-doped ones and quantum yields of alloyed ZnCdS versus CdS QDs are compared and discussed. To enhance Cu-related red emission of CdS:Cu and Zn(0.5)Cd(0.5)S:Cu core QDs, core/shell structured QDs with a wider band gap of ZnS shell are also demonstrated.