White-light-emitting diodes using semiconductor nanocrystals

Pure white-light and colour-tuning of Eu3+–Gd3+-containing metallopolymer

The first example of Eu³⁺–Gd³⁺-containing metallopolymer Poly(2-co-NVK-co-4) was constructed to exhibit tunable photoluminescence and even direct white-light emission.

Tuning emission and Stokes shift of CdS quantum dots via copper and indium co-doping

Cu and In co-doped CdS QDs are synthesized and exhibit large Stokes shifts and tunable emission from green to near-infrared.

Surface plasmon resonance mediated photoluminescence properties of nanostructured multicomponent fluorophore systems

The interaction between light and matter is the fundamental aspect of many optoelectronic applications. The efficiency of such devices is mainly dictated by the light emitting properties of fluorophores. Unfortunately, the intensity of emission is adversely affected by surface defects, scattering and chemical instability. Therefore, enhancing the luminescence of fluorophores is necessary for better implementation of nanocomposites in biological and optical applications. There are many interesting phenomena which can be observed if the characteristics of the fluorophores and metal nanoparticles are integrated. Photoluminescence (PL) by fluorophores can be enhanced or quenched by the presence of neighboring plasmonic metal nanostructures. An unambiguous study of the mechanism behind the enhancement and the quenching of emission is necessary to obtain new insight into the interactions between light and metal-fluorophore nanocomposites. In this review the core aspect of combining plasmonic metal nanostructures with fluorophores is discussed by considering various functional roles of plasmonic metals in modifying the PL properties reported by various research groups. A few representative applications of SPR mediated luminescence are also discussed.

Giant nanocrystal quantum dots: stable down-conversion phosphors that exploit a large stokes shift and efficient shell-to-core energy relaxation

A new class of nanocrystal quantum dot (NQD), the "giant" NQD (g-NQD), was investigated for its potential to address outstanding issues associated with the use of NQDs as down-conversion phosphors in light-emitting devices, namely, insufficient chemical/photostability and extensive self-reabsorption when packed in high densities or in thick films. Here, we demonstrate that g-NQDs afford significantly enhanced operational stability compared to their conventional NQD counterparts and minimal self-reabsorption losses. The latter results from a characteristic large Stokes shift (>100 nm; >0.39 eV), which itself is a manifestation of the internal structure of these uniquely thick-shelled NQDs. In carefully prepared g-NQDs, light absorption occurs predominantly in the shell but emission occurs exclusively from the core. We directly compare for the first time the processes of shell→core energy relaxation and core→core energy transfer by evaluating CdS→CdSe down-conversion of blue→red light in g-NQDs and in a comparable mixed-NQD (CdSe and CdS) thin film, revealing that the internal energy relaxation process affords a more efficient and color-pure conversion of blue to red light compared to energy transfer. Lastly, we demonstrate the facile fabrication of white-light devices with correlated color temperature tuned from ∼3200 to 5800 K.

Enhancing the conversion efficiency of red emission by spin-coating CdSe quantum dots on the green nanorod light-emitting diode

A hybrid structure of CdSe quantum dots (QDs) (λ = 640 nm) spin-coated on the indium gallium nitride (InGaN) nanorod light-emitting diode (LED, λ = 525 nm) is successfully fabricated. Experimental results indicate that the randomness and the minuteness of nanorods scatter the upcoming green light into the surrounding CdSe QDs efficiently, subsequently alleviating the likelihood of the emitted photons of red emission being recaptured by the CdSe QDs (self-absorption effect), and that increases the coupling probability of emission lights and the overall conversion efficiency. Moreover, the revealed structure with high color stability provides an alternative solution for general lighting applications of next generation.

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.

Continuous hydrothermal synthesis of nickel oxide nanoplates and their use as nanoinks for p-type channel material in a bottom-gate field-effect transistor

Nickel oxide nanoplates were continuously synthesized by hydrothermal reaction using a flow-type reactor. The products had a thickness of approximately 10 nm and a lateral size of 100-500 nm. The nanoplates were purified and drop-cast on a bottom-gate substrate and used as the channel material in a field-effect transistor after annealing at 300 degrees C. The I(d)-V(d) profile showed that the NiO nanoplates worked as the p-type semiconductor. This result suggests that various electronic devices can be prepared using metal oxide nanomaterials, which exhibit various properties including magnetism, ferroelectronics and catalysis as well as stability and safety in air and water.

CdTe Quantum Dot/Dye Hybrid System as Photosensitizer for Photodynamic Therapy

We have studied the photodynamic properties of novel CdTe quantum dots-methylene blue hybrid photosensitizer. Absorption spectroscopy, photoluminescence spectroscopy, and fluorescence lifetime imaging of this system reveal efficient charge transfer between nanocrystals and the methylene blue dye. Near-infrared photoluminescence measurements provide evidence for an increased efficiency of singlet oxygen production by the methylene blue dye. In vitro studies on the growth of HepG2 and HeLa cancerous cells were also performed, they point toward an improvement in the cell kill efficiency for the methylene blue-semiconductor nanocrystals hybrid system.