The nonlinear optical absorption properties of Au-Ag nanoparticles (NPs) were studied using an open-aperture Z-scan under a nanosecond pulsed laser with wavelengths of 450 nm, 510 nm, 550 nm, and 600 nm. The experimental results demonstrated that, when the laser intensity was 1.04 × 10¹³ W/m², the Au-Ag NPs showed saturated absorption (SA). When the laser intensity was increased to 3.03 × 10¹³ W/m², the switch from SA to reverse saturation absorption (RSA) occurred. The nonlinear absorption and its transformation were analyzed by using local surface plasmon resonance (LSPR) effect, bleaching of ground state plasmon, and free carrier absorption theory.

In this paper, WO₃ nanowires were successfully synthesized via a one-step water bath method at an appropriate temperature. The XRD (Energy Dispersive Spectrometer), SEM (Scanning electron microscope), TEM (Transmission Electron Microscope) and other characterization methods proved that the synthesized product was WO₃, and the product of water bath reaction for 9 h showed the nanowires’ structure. The nanowires were evenly distributed, and the length ranged from 2 μm to 4 μm. The results showed that the nanowires had excellent light transmittance (66%), a very short response time (1.2 s, 2 s) and excellent color rendering efficiency (115.2 cm² C⁻¹) at 650 nm. The electrochemical performance test showed that the specific capacity of the WO₃ nanowires was up to 565 F/g at 1 A/g. Change the different current densities and cycle 100 times, then return to the initial current density, accounting for 99% of the initial specific capacity of 565 F/g. We used this method for the first time to prepare tungsten oxide nanowires and investigated the bifunctional properties of the material, namely the electrochromic and capacitive properties. All of these data indicate that WO₃ nanorods have excellent electrochromic and electrochromic properties and have potential market prospects in the fields of electrochromic glass, variable glasses, advertising, and supercapacitors.

This paper aims to study the nonlinear absorption characteristics of palladium nanoparticles (PdNPs) at off-resonant wavelengths. For this purpose, multi-wavelength (500–650 nm) nanosecond Z-scan technique was used. The experimental results indicate that saturated absorption (SA) and the transition from SA to reverse saturated absorption (RSA) can occur, and depends on the excitation wavelength and energy. When the excitation wavelength is constant, with the increase of excitation energy, PdNPs change from SA to RSA. When the excitation energy is constant, with the excitation wavelength approaching surface plasmon resonance (SPR), PdNPs change from SA to RSA. This phenomenon of SA and RSA under multi-wavelength excitation in the off-resonant region provides a supplement for the systematic study of the nonlinear absorption of PdNPs.

Resonant nonlinear optical absorption of silver nanoparticles was studied experimentally via open aperture Z-scan using 130 fs, 400 nm laser pulses. Experimental results show that, at low laser intensity, silver nanoparticles can exhibit saturated absorption. While at high laser intensity, it shows reverse saturated absorption. The saturable absorption is explained in terms of ground state plasmon bleaching, while the reverse saturable absorption is believed to be from two-photon absorption. Saturable optical intensity and two-photon absorption coefficient were obtained to be $1.3\times {10}^{10} \mathrm{W}/{\mathrm{m}}^2$ and $3.3\times {10}^{-10} \mathrm{m}/\mathrm{W}$, respectively. The energy relaxation process of Ag nanoparticles after laser excitation was studied via pump-probe technique at 400 nm. Experimental results demonstrated that energy relaxation included electron-phonon coupling process with time constant ${\mathsf{\tau }}_1=\left(713\pm 50\right) \mathrm{fs}$, and phonon-phonon coupling process with time constant ${\mathsf{\tau }}_2=\left(25.2\pm 3\right) \mathrm{ps}$, respectively.

Nickel-element-doped zinc cobaltate/carbon fiber composites (Ni-ZnCo₂O₄/CF) were prepared on carbon cloth (made of a combination of carbon fibers) conductive substrates using a simple ambient stirring method combined with heat treatment. Characterization tests of the materials revealed that the prepared products were porous Ni-ZnCo₂O₄/CF mesh structures. This porous network structure increases the surface area of the material and helps shorten the diffusion path of ions and electrons. The samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) methods to investigate the effect of Ni elemental doping on the stability of the materials. The results show that there are no other impurity peaks and no other impurity elements in the Ni-ZnCo₂O₄/CF electrode material, which indicates that the sample purity is high. Meanwhile, the electrochemical properties of Ni-ZnCo₂O₄/CF electrode materials were studied. Under the condition of 15 A·g⁻¹, the specific capacitance of Ni-ZnCo₂O₄/CF electrode material is 1470 F·g⁻¹, and after 100 cycles, its specific capacity reaches 1456 F·g⁻¹, which is 99.0% of the specific capacity of 1470 F·g⁻¹, indicating that the electrode material has good stability. In addition, we assembled asymmetric supercapacitors (Ni-ZnCo₂O₄/CF//CNTs) with Ni-ZnCo₂O₄/CF as the positive material and carbon nanotubes (CNTs) as the negative material. In the cyclic stability experiment of Ni-ZnCo₂O₄/CF/CNTs devices, when the current density was 1 A·g⁻¹, the specific capacitance was 182 F·g⁻¹. After 10,000 cyclic charge–discharge tests, the specific capacity became 167 F·g⁻¹, which was basically unchanged compared with the initial specific capacity, reaching 91.8%. It shows that it has higher charge–discharge performance and higher cycle stability.