H. Y. Lin

Enhancement of band gap emission stimulated by defect loss.

Defect radiation has been always considered as the most important loss for an emitter based on band gap emission. Here, we propose a novel approach which goes against this conventional wisdom. Based on the resonance effect between the surface plasmon of metal nanoparticles and defect emission, it is possible to convert the useless defect radiation to the useful excitonic emission with a giant enhancement factor. Through the transfer of the energetic electrons excited by surface plasmon from metal nanoparticles to the conduction band of the emitter, the band gap emission can be greatly enhanced, while the defect emission can be suppressed to noise level.

Giant enhancement of band edge emission based on ZnO/TiO 2 nanocomposites

Enhancement of band edge emission of ZnO nanorods up to a factor of 120 times has been observed in the composite consisting of ZnO nanorods and TiO(2) nanoparticles, while the defect emission of ZnO nanorods is quenched to noise level. Through a detailed investigation, it is found that the large enhancement mainly arises from fluorescence resonance energy transfer between the band edge transition of ZnO nanorods and TiO(2) nanoparticles. Our finding opens up new possibilities for the creation of highly efficient solid state emitters.

Surface plasmon effects in the absorption enhancements of amorphous silicon solar cells with periodical metal nanowall and nanopillar structures

The authors numerically investigate the absorption enhancement of an amorphous Si solar cell, in which a periodical one-dimensional nanowall or two-dimensional nanopillar structure of the Ag back-reflector is fabricated such that a dome-shaped grating geometry is formed after Si deposition and indium-tin-oxide coating. In this investigation, the effects of surface plasmon (SP) interaction in such a metal nanostructure are of major concern. Absorption enhancement in most of the solar spectral range of significant amorphous Si absorption (320-800 nm) is observed in a grating solar cell. In the short-wavelength range of high amorphous Si absorption, the weakly wavelength-dependent absorption enhancement is mainly caused by the broadband anti-reflection effect, which is produced through the surface nano-grating structures. In the long-wavelength range of diminishing amorphous Si absorption, the highly wavelength-sensitive absorption enhancement is mainly caused by Fabry-Perot resonance and SP interaction. The SP interaction includes the contributions of surface plasmon polariton and localized surface plasmon.

Fabrication of surface metal nanoparticles and their induced surface plasmon coupling with subsurface InGaN/GaN quantum wells.

Based on the fabrication of Ag nanoparticles (NPs) with controlled geometry and surface density on an InGaN/GaN quantum well (QW) epitaxial structure, which contains indium-rich nano-clusters for producing localized states and free-carrier (delocalized) states in the QWs, and the characterization of their localized surface plasmon (LSP) coupling behavior with the carriers in the QWs, the interplay behavior of LSP coupling with carrier delocalization in the QWs is demonstrated. By using the polystyrene nanosphere lithography technique with an appropriate nanosphere size and adjusting the post-fabrication thermal annealing condition, the induced LSP resonance wavelength of the fabricated Ag NPs on the QW sample can match the QW emission wavelength for generating the coherent coupling between the carriers in the QWs and the induced LSP. The coupling leads to the enhancement of radiative recombination rate in the QWs and results in increased photoluminescence (PL) intensity, red-shifted PL spectrum, reduced PL decay time, and enhanced internal quantum efficiency. It is found that the observed effects are mainly due to the LSP coupling with the delocalized carriers in the QWs.

Enhancement of random lasing through fluorescence resonance energy transfer and light scattering mediated by nanoparticles

A simple approach for the enhancement of random lasing based on fluorescence resonance energy transfer and light scattering mediated by nanoparticles is reported. To illustrate our working principle, ZnO nanorods decorated with TiO2 nanoparticles were chosen as an example. It is shown that the random laser action of ZnO nanorods can be significantly improved by the assistance of TiO2 nanoparticles. Moreover, due to the inherent nature of higher refractive index of TiO2 than ZnO, the TiO2 nanoparticles can serve efficiently as better nanoscatterers, which can promote the formation of closed-loop paths. Our strategy provided here is very useful for the future development of high efficiency optoelectronic devices.

Giant enhancement of luminescence induced by second-harmonic surface plasmon resonance

Strong ultraviolet luminescence having intensity comparable with device-quality GaN epifilms has been observed in Au nanoparticles. It is identified that the luminescence involves radiative recombination of electrons in band 6 (sp conduction band) with holes in band 4 (secondary top d band), near the L symmetry point. We show that the strong emission is a consequence of the second-harmonic surface plasmon resonance (SHSPR), which is an inherent nature of metallic nanoparticles with high density of surface plasmons. The newly discovered SHSPR is very different from the conventional second-harmonic generation (SHG). In the conventional SHG, it requires an intense incident laser to generate two-photon absorption and radiation. However, for the SHSPR discussed here, we only need a weak pumping source to trigger the second-harmonic absorption of very dense surface plasmons in Au nanoclusters. In addition to Au nanoparticles, we demonstrate that SHSPR provides a very efficient way to enhance the luminescence of...

Enhancement of random lasing assisted by light scattering and resonance energy transfer based on ZnO/SnO nanocomposites

A new composite consisting of ZnO nanorods and SnO nanoparticles has been synthesized and characterized. It is found that the UV laser emission from ZnO NRs can be greatly enhanced and more easily achieved by the assistance of SnO NPs. The underlying mechanism is interpreted in terms of light scattering, charge carrier transfer and fluorescence resonance energy transfer (FRET) mediated by SnO NPs. Our strategy opens a promising route for improving the external conversion efficiency of optoelectronic devices.

Random lasing in the composites consisting of photonic crystals and semiconductor nanowires

A well designed material composed of photonic crystals (PCs) and semiconductor nanowires was proposed. To illustrate our working principle, the nanocomposites consisting of SnO2 nanowires and PCs based on Tb(OH)3/SiO2 core/shell nanospheres have been synthesized and characterized. It is found that lasing behavior can be easily achieved using this composite material. The light confined inside the PCs due to the formation of stop band can be extracted along SnO2 nanowires. The observation of random lasing behavior indicates that the composites developed here open a route for the creation of optoelectronic devices.

Laser action in Tb(OH) 3 /SiO 2 photonic crystals

Photonic crystals of Tb(OH)(3)/SiO(2) core/shell nanospheres with different periodicities were used as a resonant cavity to explore laser action. By changing the particle size, the optical stop band of the photonic crystals can be tuned to coincide with the multiple emission bands of terbium ions. An overlap of the stop band on the multiple emissions of the active materials embedded inside the photonic crystals offered a good chance for resonance. Lasing emissions arising from terbium ions occurred near the band edge of the PCs were demonstrated.

Enhancement of random lasing based on the composite consisting of nanospheres embedded in nanorods template.

A simple and general approach has been developed for the enhancement of random lasing based on the composite consisting of nanospheres and nanorods array. Due to the inherent nature of high refractive index, the selected nanorods act efficiently as scattering feedback centers, which can promote the formation of closed loop paths of the emission arising from nanospheres. To illustrate our working principle, the composite consisting of Tb(OH)(3)/SiO(2) nanospheres and ZnO nanorods was chosen as an example. Quite interestingly, it is found that the random lasing behavior can be easily achieved for the composite system, while it is absent in pure Tb(OH)(3)/SiO(2) nanospheres. The strategy demonstrated here should be very useful for the future development of coherent light emission sources and many other optoelectronic devices.