Enhancing local luminescence in a hollow ZnO microcolumn by antiresonant reflecting

Growth of CdS nanotubes and their strong optical microcavity effects

Nanotubes are often formed by the folding of one-layer or multilayer compounds under microscopic catalytic growth conditions. Here, CdS nanotubes with tunable wall sizes and optical microcavities were prepared via a simple thermal evaporation co-deposition technique with Sn metal nanowire templating and ejection. Compared to core-shell Sn/CdS nanowires, which have poor microcavity quality, the hollow/CdS nanotubes have a higher quality factor (Q) that can reach approximately 400 in the spectral range of 550-800 nm when excited by a continuous-wave 405 nm laser. This high Q factor leads to low-threshold lasing and line-width narrowing due to the mode selection, which are important in many fields, including lasers, sensors, communications, and optical storage. A theoretical mode analysis of the hollow/CdS nanotubes with different thicknesses addressed their microcavity mode confinement and enhancements. This technique provides a new way to prepare semiconductor nanotubes for new photonic devices and photoelectric applications.

Facile synthesis and optical properties of colloidal quantum dots/ZnO composite optical resonators

We present a novel colloidal quantum dot (CQD)/ZnO whispering gallery mode microcavity composite. The whispering gallery mode emission of the CQDs induced by the ZnO microcavity is realized. The resonant properties of the composite optical cavities are systematically investigated, and the obtained results are supported by finite element method simulations. The work presents a new research platform to study light–matter interactions in such a composite microcavity.

We present a facile method of incorporating CdSe/Zn_xCd_1−xS CQDs onto the surface of a ZnO WGM optical microcavity. The whispering gallery mode emission of the CQDs induced by the ZnO microcavity is directly observed.

Gradient in defect density of ZnO nanorods grown by cathodic delamination, a corrosion process, leads to end-specific luminescence

ZnO nanorods were grown on a zinc substrate via cathodic delamination of a polymer coating, a tailored corrosion process, at room temperature. A comparison between in situ Raman spectra and post mortem cross sectional analysis by Raman spectroscopy, photoluminescence spectroscopy and scanning electron microscopy shows that in the initial stages of the synthesis, preferentially defect rich ZnO grows. At later stages, crystalline wurtzite ZnO growth dominates. The result is nanorod arrays consisting of nanorods with a large density of point defects in the ≈500 nm range near the zinc substrate, and low defect density in the regions further away from the interface. The growth, which proceeds over several hours, can be interrupted at any time. Large salt concentrations in the corrosive medium increase the growth rate, but also the amount of point defects. The resulting rods show strongly position-dependent luminescence and Raman spectra. Different luminescence can thus be selectively excited, based on the position of excitation.

Improved UV response of ZnO nanotubes by resonant coupling of anchored plasmonic silver nanoparticles

In this study, plasmonic silver (Ag) nanoparticle-(NP) anchored ZnO nanorods (NRs) and nanotube-(NT) based UV photodetectors are demonstrated. Here, Ag NPs are synthesized and anchored by using a room-temperature photochemical method by exposing the precursor solution in UV radiation. In order to achieve a stronger surface plasmon resonance (SPR) and minimum agglomeration, the photochemical method is optimized with a precursor concentration of 5 mmol, a UV intensity of 0.4 mW · cm^-2, and an exposure time of 30 min. An asymmetry around 380 nm in the absorption spectra of the NP solution indicates the presence of plasmonic resonance in that region. Upon anchoring the Ag NPs, ZnO NRs show enhanced band edge emission (380-400 nm) and the emission is further significantly increased in Ag NP-anchored ZnO NTs. The on/off ratio and photoresponse properties of the UV photodetectors are enhanced significantly after anchoring Ag NPs on the ZnO nanostructures. It is believed that the near-field coupling of SPR causes an optical enhancement of ZnO, whereas the bridging effect and hot-electron transfer to the conduction band of ZnO by plasmonic Ag NPs, anchored in close proximity, gives rise to a faster response of the photodetectors.