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Halide perovskite quantum dots (PQDs) have exhibited significantly superior nonlinear optical properties compared to traditional semiconductor materials thanks to their peculiar physical and electronic structures. By further improving the nonlinear optical properties of PQDs, it is expected to adapt to ultrafast photonics applications. This work reported the nonlinear optical properties of methylammonium lead bromide-graphene (CH3NH3PbBr3-G) composites synthesized by growing CH3NH3PbBr3 quantum dots directly from a graphene oxide lattice. Our experiments indicate that the combined advantages of the ultrafast charge transport properties from graphene and the strong charge generation efficiency of perovskite can be integrated together. The CH3NH3PbBr3-G composite exhibited enhanced saturable absorption properties with large modulation depth and very low saturation intensity. The transient absorption spectra and carrier dynamics analysis revealed that the enhancement of the saturated absorption properties of the composites mainly arose from the ultrafast charge transfer between G and CH3NH3PbBr3 which promoted the coupling between different states. The results pave the way for the design of optical switches or mode lockers based on saturable absorbers with good performance.

Black phosphorus, due to its good saturation absorption properties, has great potential applications in photonics and ultrafast optoelectronics, which have attracted widespread attention. By further improving the saturation absorption of black phosphorus, it is expected to adapt to different device requirements. Here, we report the hybridization of black phosphorus nanoflakes (BPNFs) with silver nanoparticles (AgNPs) to improve the saturation absorption properties of BPNFs. High-quality AgNPs–BPNFs were synthesized by the chemical reduction method. X-ray photoelectron spectroscopy confirmed that the combination of AgNPs and BPNFs was covalent bond and partial ionic bond. Femtosecond ultrafast dynamics analysis revealed that BPNFs in the hybrids acted as an electron reservoir to transfer electrons to AgNPs, leading to an increase of carrier density and an amplification of local field intensity around AgNPs. The results show that the enhancement of the spatially localized electric field directly leads to a significant increase in the saturation absorption coefficient, modulation depth, saturation light intensity, and quality factor of AgNP–BPNF hybrids compared to pristine BPNFs, which reach 10.1 × 10–11 cm·GW–1, 19.8%, 18.6 GW·cm–2, and 1.82 × 10–13 esu cm, respectively. This was consistent with the simulation results of the finite-difference in time domain method. These investigation results imply that the saturable absorption properties of BPNFs are controllable through hybridizing with AgNPs, which suggests not only a new strategy for tuning the nonlinear optical response of BPNFs through plasma hybridization but also a physical explanation for the effect of plasma on the saturation absorption of BPNFs.

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The localized surface plasmon resonance (LSPR) properties of metal particles can be affected by their surrounding media, and the LSPR properties affect the optical properties of metal particles and their composites. However, this indirect influence of the surrounding media on optical properties is often ignored. In this regard, we have synthesized silver nanoparticles (AgNPs) and AgNPs/graphene composites, and investigated the linear and nonlinear optical properties affected by the LSPR effect that was controlled by the surrounding media of AgNPs. The structure and morphology characterization showed that the size of AgNPs and their distribution on graphene were uniform. The distribution and enhancement of the local field around the AgNPs were studied using the finite-difference time-domain (FDTD) method. The nonlinear optical properties were measured using the Z -scan technique. The results show that as the refractive index of the surrounding modification layer of AgNPs was adjusted from 1.4 to 2.5, the LSPR peak of AgNPs was redshifted more than 30 nm, the linear absorption of AgNPs/graphene was also slightly redshifted. Moreover, when the refractive index was increased to 1.9, the reverse saturation absorption of AgNPs and the saturation absorption of AgNPs/graphene both reached their maximum values, and then decreased. This investigation provides a different way to modulate optical properties of materials for possible applications in photonic devices via the appropriate LSPR effect controlled by the refractive index of the modification layers.