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. The electric field enhancement factors at both the fundamental light and the second harmonic were calculated and the enhancement factors for second harmonic generation (SHG) were estimated for the MoS2 layers with different thicknesses. Different from the MoS2 layers on a SiO2/Si substrate where the maximum SHG was observed in the single-layer MoS2, the maximum SHG was achieved in the 17 nm-thick MoS2 layer on the Au/SiO2 substrate. As compared with the MoS2 layers on the SiO2/Si substrate, a significant enhancement in SHG was found for the MoS2 layers on the Au/SiO2 substrate due to the strong localization of the electric field. More interestingly, it was demonstrated experimentally that optical data storage can be realized by modifying the SHG intensity of a MoS2 layer through thinning its thickness.

Achieving intense nearly white upconversion emission from a single β-NaYF4:Yb/Er microcrystal via saturated excitation.

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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.

Metal halide perovskites have attracted great interest in recent years and their emission wavelength can be adjusted either by doping impurities or by exploiting quantum size effect. Here, it is reported that the realization of optically‐controlled quantum size effect in a hybrid nanocavity composed of a perovskite (CsPbBr3) nanoparticle and a thin gold (Au) film. Such nanocavities are created by synthesizing polycrystalline CsPbBr3 nanoparticles composed of quantum dots on a thin Au film via chemical vapor deposition, which emit luminescence at ≈488 nm under the excitation of femtosecond laser pulses with a low repetition rate. The phase transition from polycrystalline to monocrystalline, which quenches the quantum size effect and shifts the emission wavelength to ≈515 nm, can be introduced in CsPbBr3 nanoparticles by simply increasing the laser power. Interestingly, such a phase transition is reversible provided that the laser power is lower than a threshold. Consequently, four optical states including dual‐wavelength emission, can be achieved by deliberately setting the laser power. The underlying physical mechanism is unveiled by the static and transient temperature distributions simulated for the hybrid nanocavity. The findings open a new avenue for designing novel photonic devices based on perovskite nanoparticles and plasmonic nanostructures.