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Integrationof miniaturized elements has been a major driving forcebehind modern photonics. Nanowires have emerged as potential buildingblocks for compact photonic circuits and devices in nanophotonics.We demonstrate here a single nanowire optical correlator (SNOC) forultrafast pulse characterization based on imaging of the second harmonic(SH) generated from a cadmium sulfide (CdS) nanowire by counterpropagatingguided pulses. The SH spatial image can be readily converted to thetemporal profile of the pulses, and only an overall pulse energy of8 μJ is needed to acquire a clear image of 200 fs pulses. Sucha correlator should be easily incorporated into a photonic circuitfor future use of on-chip ultrafast optical technology. [ABSTRACT FROM AUTHOR]

3,6-Carbazole precursors were used to prepare an octaphyrin. The conformation and electronic structure of the system could be modulated through trifluoroacetate (TFA) protonation and BF 2 complexation. The resulting nonaromatic macrocyclic complexes, 2-2TFA and 2-2BF 2 , displayed noteworthy photophysical properties. For instance, the diprotonated species 2-2TFA showed a strong panchromic absorption up to 800 nm, while the bis-BF 2 -chelated dipyrromethene (BODIPY)-like complex 2-2BF 2 exhibited an intense visible absorption feature (ε 535nm = 2.1 × 10 5 M -1 cm -1 ), as well as a relatively red-shifted emission at 640 nm characterized by a large Stokes shift. It was found that 2-2BF 2 could be used to construct a high-quality organic microlaser that functions under optical pumping. The present study highlights the potential utility of expanded porphyrins as possible laser dyes.

Organometal halide perovskite has recently emerged as a very promising family of materials with augmented performance in electronic and optoelectronic applications including photovoltaic devices, photodetectors, and light-emitting diodes. Herein, we propose and demonstrate facile solution synthesis of a series of colloidal organometal halide perovskite CH3NH3PbX3 (X = halides) nanoparticles with amorphous structure, which exhibit high quantum yield and tunable emission from ultraviolet to near-infrared. The growth mechanism and photoluminescence properties of the perovskite amorphous nanoparticles were studied in detail. A high-efficiency green-light-emitting diode based on amorphous CH3NH3PbBr3 nanoparticles was demonstrated. The perovskite amorphous nanoparticle-based light-emitting diode shows a maximum luminous efficiency of 11.49 cd/A, a power efficiency of 7.84 lm/W, and an external quantum efficiency of 3.8%, which is 3.5 times higher than that of the best colloidal perovskite quantum-dot-based light-emitting diodes previously reported. Our findings indicate the great potential of colloidal perovskite amorphous nanoparticles in light-emitting devices.

Controlling nonlinear light-matter interaction is important from a fundamental science point of view as well as a basis for future optoelectronic devices. Recent advances in two-dimensional crystals have created opportunities to manipulate nonlinear processes electrically. Here we report a strong second-harmonic generation (SHG) in a 2D WSe2 bilayer crystal caused by a back gate field. This unusual process takes place only when the gate polarity causes charge accumulation rather than depletion. Analysis based on a bond-charge model traces the origin of SHG to the nonuniform field distribution within a single monolayer, caused by the accumulated submonolayer screening charge in the tungsten plane. We name this phenomenon charge-induced SHG (CHISHG), which is fundamentally different from the field- or current-induced SHG. Our findings provide a potentially valuable technique for understanding and noninvasive probing of charge and current distributions in future low dimensional electronic devices.

We demonstrate single-mode laser emission in single nanowires. By folding a 200 nm diameter CdSe nanowire to form loop mirrors, single-mode laser emission around 738 nm wavelength is obtained with line width of 0.12 nm and low threshold. The mode selection is realized by the vernier effect of coupled cavities in the folded nanowire. In addition, the loop structure makes it possible to tune the nanowire cavity, opening an opportunity to realize a tunable single-mode nanowire laser.

Bandgap engineering of semiconductor nanowires is important in designing nanoscale multifunctional optoelectronic devices. Here, we report a facile thermal evaporation method, and realize the spatial bandgap engineering in single CdS(1-x)Se(x) alloy nanowires. Along the length of these achieved nanowires, the composition can be continuously tuned from x = 0 (CdS) at one end to x = 1 (CdSe) at the other end, resulting in the corresponding bandgap (light emission wavelength) being modulated gradually from 2.44 eV (507 nm, green light) to 1.74 eV (710 nm, red light). In spite of the existing composition (crystal lattice) transition along the length, these multicolor nanowires still possess high-quality crystallization. These bandgap engineered nanowires will have promising applications in such as multicolor display and lighting, high-efficiency solar cells, ultrabroadly spectral detectors, and biotechnology.

We report a general approach to light-emitting polymer nanofibers (PNFs) based on waveguiding excitation. By waveguiding excitation light along the PNFs, we demonstrated that the interaction of light with PNFs is enhanced over 3 orders of magnitude compared with the currently used irradiating excitation. Intriguing advantages such as enhanced excitation efficiency, low excitation power operation down to nW levels, tightly confined excitation with low cross talk, and high photostability of the light-emitting PNFs are obtained. The waveguiding excitation allows incorporation of various fluorescent dyes into PNFs to generate multicolor emitting sources covering the entire visible spectrum. The light-emitting single PNFs via waveguiding excitation may find widespread nanophotonic applications in chemical and biological sensors, multicolor emitting sources, and lasers.

We report direct coupling of plasmonic and photonic nanowires using ultracompact near-field interaction. Photon-plasmon coupling efficiency up to 80% with coupling length down to the 200 nm level is achieved between individual Ag and ZnO nanowires. Hybrid nanophotonic components, including polarization splitters, Mach-Zehnder interferometers, and microring cavities, are fabricated out of coupled Ag and ZnO nanowires. These components offer relatively low loss with subwavelength confinement; a hybrid nanowire microcavity exhibits a Q-factor of 520.