This Review article summarizes the key advantages of using quantum dots (QDs) as luminophores in light-emitting devices (LEDs) and outlines the operating mechanisms of four types of QD-LED. The key scientific and technological challenges facing QD-LED commercialization are identified, together with on-going strategies to overcome these challenges.

Emergence of colloidal quantum-dot light-emitting technologies

The presence of tiny holes in an opaque metal film, with sizes smaller than the wavelength of incident light, leads to a wide variety of unexpected optical properties such as strongly enhanced transmission of light through the holes and wavelength filtering. These intriguing effects are now known to be due to the interaction of the light with electronic resonances in the surface of the metal film, and they can be controlled by adjusting the size and geometry of the holes. This knowledge is opening up exciting new opportunities in applications ranging from subwavelength optics and optoelectronics to chemical sensing and biophysics.

Light in tiny holes

We present a review of current research on the optical properties of ZnO nanostructures. We provide a brief introduction to different fabrication methods for various ZnO nanostructures and some general guidelines on how fabrication parameters (temperature, vapor-phase versus solution-phase deposition, etc.) affect their properties. A detailed discussion of photoluminescence, both in the UV region and in the visible spectral range, is provided. In addition, different gain (excitonic versus electron hole plasma) and feedback (random lasing versus individual nanostructures functioning as Fabry-Perot resonators) mechanisms for achieving stimulated emission are described. The factors affecting the achievement of stimulated emission are discussed, and the results of time-resolved studies of stimulated emission are summarized. Then, results of nonlinear optical studies, such as second-harmonic generation, are presented. Optical properties of doped ZnO nanostructures are also discussed, along with a concluding outlook for research into the optical properties of ZnO.

Optical properties of ZnO nanostructures.

Transparent conductors as solar energy materials: A panoramic review

This review provides a perspective on the recent developments in the transmission of light through subwavelength apertures in metal films. The main focus is on the phenomenon of extraordinary optical transmission in periodic hole arrays, discovered over a decade ago. It is shown that surface electromagnetic modes play a key role in the emergence of the resonant transmission. These modes are also shown to be at the root of both the enhanced transmission and beaming of light found in single apertures surrounded by periodic corrugations. This review describes both the theoretical and experimental aspects of the subject. For clarity, the physical mechanisms operating in the different structures considered are analyzed within a common theoretical framework. Several applications based on the transmission properties of subwavelength apertures are also addressed.

http://digital.csic.es/bitstream/10261/47904/1/Light%20passing.pdf

Light passing through subwavelength apertures

Colloidal CdSe nanocrystals (NCs) with high photoluminescent quantum yield are fabricated by a method adopting a large initial Se:Cd ratio of the precursors in the solution. X-ray diffraction and Raman measurements confirm that there exists lattice contraction in the free-standing wurtzite CdSe NCs. The lattice contraction indicates the occurrence of surface optimization/reconstruction during the growth, which results in the high quantum yield of the obtained CdSe NCs.

Lattice contraction in free-standing CdSe nanocrystals

The structural and optical properties of ZnO nanorod arrays

Monodisperse colloidal CdSe nanocrystals (NCs) with different sizes were synthesized, and the time-resolved photoluminescence (PL) spectra were measured to explore the evolution of surface states during the NC’s growth. The PL quantum yield, fluorescence lifetime, and the surface-related emission had the identical size dependence. The role of the nonradiative/radiative surface states in the PL carrier dynamics was discussed.

Size-Dependent Time-Resolved Photoluminescence of Colloidal CdSe Nanocrystals

We report experimental results on enhanced light transmission through two periodically perforated metal films separated by a layer of dielectric. A perforated metal film (single metallic structure) exhibits extraordinary optical transmission, and when two such perforated metal films are spaced by a dielectric layer (cascaded metallic structure), the transmission is further increased. The maximum transmission of the cascaded metallic structure, which depends on the distance between the two metal films, can be more than 400% greater than that of a corresponding single metallic structure. It is proposed that the coupling of surface plasmon polaritons between the two metal films is involved in the process.

Enhanced light transmission through cascaded metal films perforated with periodic hole arrays.

Photo-oxidation of densely packed monolayer of CdSe quantum dots (QDs) was studied by time-resolved photoluminescence (PL) spectroscopy. Electrons yielded in QDs by the strong laser-pulse irradiation can assist the oxidation of CdSe QDs. Such rapid photo-oxidation does not introduce more nonradiative defects, instead, it enhances the coupling between QDs through surface modification and the PL intensity can be significantly improved.

Jiayu Zhang

Papers

Lattice contraction in free-standing CdSe nanocrystals

The structural and optical properties of ZnO nanorod arrays

Size-Dependent Time-Resolved Photoluminescence of Colloidal CdSe Nanocrystals

Enhanced light transmission through cascaded metal films perforated with periodic hole arrays.

Photo-oxidation-enhanced coupling in densely packed CdSe quantum-dot films