Constructing Type-II and S-Scheme Heterojunctions of CuO@Cu(SO)(OH)·HO Polyhedra by In Situ Etching CuO with Different Exposed Facets for Enhanced Photocatalytic Sterilization and Degradation Performance.

The construction of type-II or S-scheme heterojunctions can effectively accelerate the directional migration of charge carriers and inhibit the recombination of electron-hole pairs to improve the catalytic performance of the composite catalyst; therefore, the construction and formation mechanism of a heterojunction are worth further investigation. Herein, CuO@Cu(SO)(OH)·HO core-shell polyhedral heterojunctions were fabricated via in situ etching CuO with octahedral, cuboctahedral, and cubic shapes by sodium thiosulfate (NaSO). CuO@Cu(SO)(OH)·HO polyhedral heterojunctions demonstrated obviously enhanced sterilization and degradation performance than the corresponding single CuO polyhedra and Cu(SO)(OH)·HO.

Turning a polystyrene microsphere into a multimode light source by laser irradiation.

Polystyrene (PS) is generally considered as a passive optical material that is transparent to light with wavelengths longer than 300 nm. In practice, PS micro- and nanospheres with uniform sizes are usually used to build photonic crystals based on self-assembly mechanism. Here, we demonstrate experimentally that PS microspheres supporting whispery gallery modes can be transformed into multimode light sources by laser irradiation.

Controllable Formation of Luminescent Carbon Quantum Dots Mediated by the Fano Resonances Formed in Oligomers of Gold Nanoparticles.

Rapid and controllable formation of fluorescent carbon quantum dots (CQDs) is highly desirable in the fields of nanophotonics and biophotonics. Here, a novel strategy for creating CQDs, which emit white light efficiently under the excitation of either laser light or a mercury lamp, is proposed and demonstrated. The luminescent CQDs are generated by irradiating a poly(vinyl alcohol) (PVA) film doped with dense gold nanoparticles (AuNPs) with femtosecond laser pulses.

Multipole Radiations from Large Gold Nanospheres Excited by Evanescent Wave.

We proposed the use of the evanescent wave generated in a total internal reflection configuration to excite large gold nanospheres and investigated the radiations of the high-order plasmon modes supported in gold nanospheres. It was revealed that the evanescent wave excitation is equivalent to the excitation by using both the incident and reflected light, offering us the opportunity to control the orientation of the electric field used to excite nanoparticles. In addition, it was found that the scattering light intensity is greatly enhanced and the background noise is considerably suppressed, making it possible to detect the radiations from high-order plasmon modes.

A Novel Fast Photothermal Therapy Using Hot Spots of Gold Nanorods for Malignant Melanoma Cells.

In this paper, the plasmon resonance effects of gold nanorods was used to achieve rapid photothermal therapy for malignant melanoma cells (A375 cells). After incubation with A375 cells for 24 h, gold nanorods were taken up by the cells and gold nanorod clusters were formed naturally in the organelles of A375 cells. After analyzing the angle and space between the nanorods in clusters, a series of numerical simulations were performed and the results show that the plasmon resonance coupling between the gold nanorods can lead to a field enhancement of up to 60 times.

All-silicon-based nano-antennas for wavelength and polarization demultiplexing.

We propose an all-silicon-based nano-antenna that functions as not only a wavelength demultiplexer but also a polarization one. The nano-antenna is composed of two silicon cuboids with the same length and height but with different widths. The asymmetric structure of the nano-antenna with respect to the electric field of the incident light induced an electric dipole component in the propagation direction of the incident light.

Radiation of the high-order plasmonic modes of large gold nanospheres excited by surface plasmon polaritons.

Large metallic nanoparticles with sizes comparable to the wavelength of light are expected to support high-order plasmon modes exhibiting resonances in the visible to near infrared spectral range. However, the radiation behavior of high-order plasmon modes, including scattering spectra and radiation patterns, remains unexplored. Here, we report on the first observation and characterization of the high-order plasmon modes excited in large gold nanospheres by using the surface plasmon polaritons generated on the surface of a thin gold film.

Modifying the mechanical properties of gold nanorods by copper doping and triggering their cytotoxicity with ultrasonic wave.

We proposed the use of copper (Cu) doping to modify the mechanical properties of gold nanorods (AuNRs) and demonstrated the triggering of the cytotoxicity of Cu-doped AuNRs with ultrasonic wave. The mechanical properties of Cu-doped AuNRs were analyzed theoretically by using the density-function calculation and it was found that Cu-Au bond is much weaker than Au-Au bond. In experiments, AuNRs without and with Cu doping were synthesized and they were found to be low cytotoxic to both human liver hepatocellular carcinoma (HepG2) cells and normal liver cells (L02).

Photothermal therapy of single cancer cells mediated by naturally created gold nanorod clusters.

Gold nanorods (GNRs) are generally considered to be nontoxic to normal and cancer cells. They are usually accumulated at lysosomes after entering into cells, forming GNR clusters in which strong plasmonic coupling between GNRs is expected. We investigated the photothermal therapy of single cancer cells by exploiting the significantly enhanced two-photon-induced absorption of GNR clusters naturally created in the lysosomes of cancer cells.

Encoding Random Hot Spots of a Volume Gold Nanorod Assembly for Ultralow Energy Memory.

Data storage with ultrahigh density, ultralow energy, high security, and long lifetime is highly desirable in the 21st century and optical data storage is considered as the most promising way to meet the challenge of storing big data. Plasmonic coupling in regularly arranged metallic nanoparticles has demonstrated its superior properties in various applications due to the generation of hot spots. Here, the discovery of the polarization and spectrum sensitivity of random hot spots generated in a volume gold nanorod assembly is reported.

Hot-Electron Intraband Luminescence from GaAs Nanospheres Mediated by Magnetic Dipole Resonances.

Significantly enhanced electric field in plasmonic hot spots can dramatically increase the linear and nonlinear absorption of light, leading to a high-temperature electron gas which radiates, through mainly intraband transition, a broadband luminescence quite similar to blackbody radiation. Here, we demonstrate that such hot-electron intraband luminescence (HEIL) can also be achieved by exploiting the significantly enhanced electric field at the magnetic dipole resonances of gallium arsenide (GaAs) nanospheres (NSs). We show that monocrystalline GaAs NSs with distinct electric and magnetic dipole (ED and MD) resonances can be obtained by using femtosecond laser ablation and annealing.

Hot luminescence from gold nanoflowers and its application in high-density optical data storage.

Gold nanoflowers with feature sizes ranging from several tenths to several hundred nanometers were synthesized by using the one-pot method. They were formed by the self-organization of gold nanoparticles of several nanometers and exhibited broad extinction spectra in the near infrared spectral range. Randomly distributed hot spots originating from the strongly localized modes were generated in gold nanoflowers and their appearances exhibited strong dependences on both the polarization and wavelength of the excitation light.

Influence of a three-dimensional photonic crystal on the plasmonic properties of gold nanorods.

The influence of a three-dimensional (3D) photonic crystal (PC) on the plasmonic properties of gold nanorods (GNRs), which are placed on the surface of the PC, was investigated both numerically and experimentally. The 3D PC formed by closely packed polystyrene spheres was fabricated by using a pressure controlled isothermal heating vertical deposition technique. For a GNR whose longitudinal surface plasmon resonance (LSPR) is located at the bandgap edges of the PC, a dramatic narrowing of the absorption spectrum as well as an enhancement in electric field and thus the absorption was observed.

Polarization beam splitters, converters and analyzers based on a metasurface composed of regularly arranged silicon nanospheres with controllable coupling strength.

A metasurface composed of regularly arranged silicon (Si) nanospheres (NSs) with coupling was investigated both theoretically and numerically based on the Mie theory, the simple Lorentz line shape model and the finite-difference time-domain technique. By deliberately controlling the coupling strength between Si NSs through the design of the lattice constants of a rectangular lattice, polarization beam splitters, converters and analyzers with good performance can be successfully constructed. A square lattice as well as a large incidence angle was employed to build the polarization beam splitters and converters.

Controlling the Two-Photon-Induced Photon Cascade Emission in a Gd(3+)/Tb(3+)-Codoped Glass for Multicolor Display.

We reported the first observation of the two-photon-induced quantum cutting phenomenon in a Gd(3+)/Tb(3+)-codoped glass in which two photons at ~400 nm are simultaneously absorbed, leading to the cascade emission of three photons in the visible spectral region. The two-photon absorption induced by femtosecond laser pulses allows the excitation of the energy states in Gd(3+) which are inactive for single-photon excitation and enables the observation of many new electric transitions which are invisible in the single-photon-induced luminescence. The competition between the two-photon-induced photon cascade emission and the single-photon-induced emission was manipulated to control the luminescence color of the glass.

Effects of substrates on the nonlinear optical responses of two-dimensional materials.

We investigated numerically and experimentally the achievement of strongly localized electric field and significantly enhanced second harmonic generation (SHG) in two-dimensional (2D) materials by using dielectric-metal hybrid substrates. Based on the theory of thin film interference, it was revealed that the strongest localization of electric field in a 2D material, which corresponds to the largest absorption in the metal film, could be achieved by minimizing the reflection of the combined structure (i.e.

Enhanced upconversion luminescence from ZnO/Zn hybrid nanostructures induced on a Zn foil by femtosecond laser ablation.

ZnO/Zn hybrid nanostructures including nanowires and nanonets were induced on a Zn foil by using 400-nm femtosecond (fs) laser pulses with a low repetition rate of 1 kHz and duration of 100 fs. The laser fluence was chosen to be slightly above the ablation threshold of Zn. The luminescence of the formed ZnO/Zn hybrid nanostructures was examined by using fs laser pulses with a high repetition rate of 76 MHz and duration of ~130 fs through both single-photon and multiphoton excitation.

Revealing silent vibration modes of nanomaterials by detecting anti-Stokes hyper-Raman scattering with femtosecond laser pulses.

We proposed a scheme in which normal Raman scattering is coupled with hyper-Raman scattering for generating a strong anti-Stokes hyper-Raman scattering in nanomaterials by using femtosecond laser pulses. The proposal was experimentally demonstrated by using a single-layer MoS2 on a SiO2/Si substrate, a 17 nm-thick MoS2 on an Au/SiO2 substrate and a 9 nm-thick MoS2 on a SiO2-SnO2/Ag/SiO2 substrate which were confirmed to be highly efficient for second harmonic generation. A strong anti-Stokes hyper-Raman scattering was also observed in other nanomaterials possessing large second-order susceptibilities, such as silicon quantum dots self-assembled into "coffee" rings and tubular Cu-doped ZnO nanorods.

Three-photon-induced blue emission with narrow bandwidth from hot flower-like ZnO nanorods.

ZnO nanorods (NRs) self-organized into flowers were synthesized at different temperatures ranging from 100°C to 180°C by using the hydrothermal method. The existence of Zn interstitials (Zn(i)) was confirmed by X-ray photoelectron spectroscopy and a larger amount of Zn(i) was found in the ZnO NRs prepared at higher temperatures. A redshift of the emission peak of more than 15 nm was observed for the ZnO NRs under single photon excitation.

Enhanced second harmonic generation of MoS2 layers on a thin gold film.

The linear and nonlinear optical properties of thin MoS2 layers exfoliated on an Au/SiO2 substrate were investigated both numerically and experimentally. It was found that the MoS2 layers with different thicknesses exhibited different colors on the gold film. The reflection spectra of the MoS2 layers with different thicknesses were calculated by using the finite-difference time-domain technique and the corresponding chromaticity coordinates were derived.

Formation of 100-nm periodic structures on a titanium surface by exploiting the oxidation and third harmonic generation induced by femtosecond laser pulses.

Periodic surface structures with periods as small as about one-tenth of the irradiating femtosecond (fs) laser light wavelength were created on the surface of a titanium (Ti) foil by exploiting laser-induced oxidation and third harmonic generation (THG). They were achieved by using 100-fs laser pulses with a repetition rate of 1 kHz and a wavelength ranging from 1.4 to 2.

Controllable color display induced by excitation-intensity-dependent competition between second and third harmonic generation in ZnO nanorods.

We investigated the second and third harmonic generation (SHG and THG) in ZnO nanorods (NRs) by using a femtosecond laser (optical parametric amplifier with tunable wavelengths) with a long excitation wavelength of 1350 nm and a low repetition rate of 1 kHz. The damage threshold for ZnO NRs in this case was sufficiently large, enabling us to observe the competition between SHG and THG. The transition from red to blue emission and the mixing of red and blue light with different ratios were successfully demonstrated by simply varying excitation intensity, implying the potential applications of ZnO NRs in all-optical display.

Competition between second harmonic generation and two-photon-induced luminescence in single, double and multiple ZnO nanorods.

The nonlinear optical properties of single, double and multiple ZnO nanorods (NRs) were investigated by using a focused femtosecond (fs) laser beam. The excitation wavelength of the fs laser was intentionally chosen to be 754 nm at which the energy of two photons is slightly larger than that of the exciton ground state but smaller than the bandgap energy of ZnO. Second harmonic generation (SHG) or/and two-photon-induced luminescence (TPL) were observed and their dependences on excitation density were examined.

Three-dimensional orientation sensors by defocused imaging of gold nanorods through an ordinary wide-field microscope.

Gold (Au) nanoparticles, particularly nanorods, are actively employed as imaging probes because of their special nonblinking and nonbleaching absorption, scattering, and emitting properties that arise from the excitation of surface plasmons. Herein, we report a novel sensing method that detects feature orientation at the nanoscale via the defocused imaging of individual Au nanorods (AuNRs) with an ordinary wide-field optical microscope. By simultaneously recording defocused images and two-photon luminescence intensities for a large number of individual AuNRs, we correlate their defocused images with their three-dimensional spatial orientations.

Fabrication of novel luminor Y(2)O(3):Eu(3+)@SiO(2)@YVO(4):Eu(3+) with core/shell heteronanostructure.

A novel polychromic phosphor with core-shell heteronanostructure has been prepared to improve the chromatic index of phosphors. As for the first example, Y(2)O(3):Eu(3+)@SiO(2)@YVO(4):Eu(3+), its synthetic route, structure and optical properties are presented in this paper. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), energy-dispersive x-ray spectra (EDS) and photoluminescence (PL) were all employed to characterize the composite core-shell phosphors.