Changgui Lv

Whispering gallery-mode lasing in ZnO microrods at room temperature

An individual hexagonal ZnO microrod was employed as a whispering-gallery mode (WGM) microcavity to obtain ultraviolet lasing at room temperature. The WGM lasing shows a low threshold, a high quality factor, and distinct mode structure. A typical stimulated emission from the ZnO microrod with diagonal of 6.67 μm exhibits a low lasing threshold of 255 kW/cm2. The observed discrete lasing modes match with the simulated positions very well. The spatial distribution of the lasing intensity demonstrates the lasing output direction and provides the direct evidence of the WGM resonant mechanism. We systematically investigated the lasing performance for different sized microrods.

Two-photon excited whispering-gallery mode ultraviolet laser from an individual ZnO microneedle

Wurtzite structural ZnO microneedles with hexagonal cross section were fabricated by vapor-phase transport method and an individual microneedle was employed as a lasing microcavity. Under excitation of a femtosecond pulse laser with 800 nm wavelength, the ultraviolet (UV) laser emission was obtained, which presented narrow linewidth and high Q value. The UV emission, resonant mechanism, and laser mode characteristics were discussed in detail. The results demonstrated that the UV laser originated from the whispering-gallery mode induced by two-photon absorption assisted by Rabi oscillation.

Combined whispering gallery mode laser from hexagonal ZnO microcavities

The hexagonal ZnO microrods were employed as whispering gallery mode (WGM) microcavities to obtain ultraviolet laser at room temperature. For each individual ZnO microrod, the laser presented low threshold and high quality Q factor and clear WGM spectral structure. The lasing spectra from different microcavities were combined together by pumping two or more ZnO microrods simultaneously. The resonant process and lasing characteristics, such as lasing mode, threshold, and Q factor, were investigated in experiment and theory.

Coherent Control of Optical Spin‐to‐Orbital Angular Momentum Conversion in Metasurface

Efficient control over the conversion of optical angular momentum from spin to orbital form in a metasurface system is achieved. Under coherent symmetric incidence, it can support nearly 100% conversion and unitary output, while it can support 50% conversion with 25% transmittance under one beam incidence.

Nonlinear optical response of semiconductor-nanocrystals-embedded photonic band gap structure

Colloidal CdSe/ZnS core/shell nanocrystals (NCs), which were dispersed in SiO2 sol, were utilized to fabricate a SiO2:NCs/TiO2 all-dielectric photonic band gap (PBG) structure. The third-order nonlinear refractive index (n2) of the PBG structure was nearly triple of that of the SiO2:NCs film due to the local field enhancement in the PBG structure. The photoinduced change in refractive index (Δn) could shift the PBG band edge, so the PBG structure would show significant transmission modification, whose transmission change was ∼17 folds of that of the SiO2:NCs film. Under excitation of a 30 GW/cm2 femtosecond laser beam, a transmission decrease of 80% was realized.

Evanescent waves of an annular left-handed material lens

The imaging system formed by an annular left-handed material (LHM) lens as well as the evanescent waves in the lens are simulated numerically with a finite-difference time-domain (FDTD) method. For b-ag\lambda (a and b are respectively the inner and outer radii of the annular lens, and \lambda is the wavelength), when a point source is placed at an internal grid point, we demonstrate that the evanescent waves are produced around the internal interface, and cannot propagate outwards. As for b-al\lambda, the evanescent waves appear around both the internal and the external interfaces, which remarkably implies the coupling between the two interfaces. Hence it can be inferred that the evanescent waves around the external interface participating in the super-resolution imaging result from the coupling of the evanescent waves around the interface. Moreover, the partly uncomprehended properties of the evanescent waves in the LHM slab are also disclosed. It is conducive to understanding the evanescent waves in the LHMs further.

Joint effect of ferromagnetic and non-ferromagnetic cations for adjusting room temperature ferromagnetism of highly luminescent CuNiInS quaternary nanocrystals.

In this work, highly luminescent quaternary CuNiInS nanocrystals (NCs) are put forward as a good prototype for investigating defect-induced room temperature ferromagnetism. A ferromagnetic Ni cation can preserve the strong luminescence of NCs without introducing intermediate energy levels in the center of the forbidden band. The strong luminescence of NCs is used as an indicator for monitoring the concentration of vacancy defects inside them, facilitating the investigation of the origin of room temperature ferromagnetism in CuNiInS NCs. Our results reveal that the patching of Cu vacancies [Formula: see text] with Ni will result in bound magnetic polarons composed of both [Formula: see text] and a substitution of Cu by Ni [Formula: see text] giving rise to the room temperature ferromagnetism of CuNiInS NCs. Either the ferromagnetic Ni or the non-ferromagnetic Cu cation can tune the magnetism of CuNiInS NCs because of the change of bound magnetic polaron concentration at the altered concentration ratio of [Formula: see text] and [Formula: see text].

Size-dependent dual emission of Cu,Mn:ZnSe QDs: Controlling both emission wavelength and intensity

Cu,Mn:ZnSe quantum dots (QDs) of tunable size, controllable photoluminescence (PL) intensity ratio and PL range were prepared. A study of the experimental conditions confirmed that the size of Cu,Mn:ZnSe QDs is affected by the pH of the solution, the speed at which the Zn solution is injected and the reaction temperature. In general, high pH, low injection speed and high reaction temperature are optimal for preparing large QDs. Based on this knowledge, different sizes of Cu,Mn:ZnSe QDs were synthesized. Moreover, white emission Cu,Mn:ZnSe QDs were designed by controlling the experimental conditions and the feeding mole ratio of Mn:Cu.

Configurations and characteristics of boron and B36 clusters

Characteristics of the ring and linear structures of the boron cluster B36 and its doped clusters were investigated with DFT/B3LYP/6-31G. The results illustrate that the ring B3 structure is the most stable configuration compared with other rings. Odd and even linear structures have different bonding; there is one different bond in the center of even linear structures, while the remaining bonds have left and right symmetry. The B36 cluster upholds the configuration rule of pure ring and linear molecules. However, the N-doped B36N cluster exhibits obvious distortion compared with the B36 molecule. The impurity N changes the structure of the energy band of the B36 cluster. The wavelength of absorption spectra and electronic circular dichroism of the N-doped B36N cluster shifts to a longer wavelength compared with that of the B36 cluster.

Design and assembly of an aqueous red CdTe QD-LED: major factors to fabricate aqueous QD-LEDs

The first aqueous red CdTe QD-LED was fabricated with the structure of ITO/PEDOT:PSS/PVK/CdTe QDs/ZnO/Al. The device has been considered to be an advanced aqueous QD-LED, which demonstrated a turn-on voltage of about 5 V. Further, its current density and brightness would also reach 92 mA cm−2 and 58 cd m−2 at the voltage of 10 V. Moreover, we found that there were two essential factors for fabricating an aqueous QD-LED successfully: (1) adding wet agent to the QD solution, (2) removing the composite ions remaining in the QD solution. Meanwhile, the EL intensity of the aqueous QD-LEDs will perform better if the solution of QDs is acidic. These results offer a promising approach to the further development of aqueous QD-LEDs.