Abstract:Recently lead halide nanocrystals (quantum dots) have been reported with potential for photovoltaic and optoelectronic applications due to their excellent luminescent properties. Herein excitonic photoluminescence (PL) excited by two-photon absorption in perovskite CsPbBr3 quantum dots (QDs) have been studied across a broad temperature range from 80K to 380K. Twophoton absorption has been investigated with absorption coefficient up to 0.085 cm/GW at room temperature. Moreover, the photoluminescence excited by two-photon absorption shows a linear blue-shift (0.25meV/K) below temperature of ~220K and turned steady with fluctuation below 1nm (4.4meV) for higher temperature up to 380K. These phenomena are distinctly different from general red-shift of semiconductor and can be explained by the competition between lattice expansion and electron−phonon coupling. Our results reveal the strong nonlinear absorption and temperatureindependent chromaticity in a large temperature range from 220K to 380K in the CsPbX3 QDs, which will offer new opportunities in nonlinear photonics, light-harvesting and light-emitting devices.

The year 2019 marks the 10th anniversary of the first report of ultrafast fiber laser mode-locked by graphene. This result has had an important impact on ultrafast laser optics and continues to offer new horizons. Herein, we mainly review the linear and nonlinear photonic properties of two-dimensional (2D) materials, as well as their nonlinear applications in efficient passive mode-locking devices and ultrafast fiber lasers. Initial works and significant progress in this field, as well as new insights and challenges of 2D materials for ultrafast fiber lasers, are reviewed and analyzed.

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The 2D semiconductor monolayer transition metal dichalcogenides, WS and MoS , are grown by chemical vapor deposition (CVD) and assembled by sequential transfer into vertical layered heterostructures (VLHs). Insulating hBN, also produced by CVD, is utilized to control the separation between WS and MoS by adjusting the layer number, leading to fine-scale tuning of the interlayer interactions within the VLHs. The interlayer interactions are studied by photoluminescence (PL) spectroscopy and are demonstrated to be highly sensitive to the input excitation power. For thin hBN separators (one to two layers), the total PL emission switches from quenching to enhancement by increasing the laser power. Femtosecond broadband transient absorption measurements demonstrate that the increase in PL quantum yield results from Förster energy transfer from MoS to WS . The PL signal is further enhanced at cryogenic temperatures due to the suppressed nonradiative decay channels. It is shown that (4 ± 1) layers of hBN are optimum for obtaining PL enhancement in the VLHs. Increasing thickness beyond this causes the enhancement factor to diminish, with the WS and MoS then behaving as isolated noninteracting monolayers. These results indicate how controlling the exciton generation rate influences energy transfer and plays an important role in the properties of VLHs.

Silicon (Si) photonics have established as leading technologies in addressing the rapidly increasing demands of huge data transfer in optical communication systems with compact footprints, small power consumption, and ultradense bandwidth, which are driven by the next generation supercomputers and big data era. Particularly, Si photonics will penetrate into optical communication links at an ever-small scale, namely chip-to-chip and on-chip. However, the nanostructures made of Si with an indirect bandgap are not ideal candidates for on-chip light sources, modulators, and photodetectors, which most-frequently require optical materials with direct bandgap. Thanks to the advent of graphene, transition metal dichalcogenides and other two-dimensional (2D) materials, which can facilitate extraordinary progresses in improving device performance at the ultrathin scale, their integration with Si photonics furnishes a heterogeneous platform to construct fully functional and highly integrated photonic communication systems. In this work, the current advancements in the on-chip applications of Si photonics-2D materials heterostructures, inclusive of all essential chip-scale modules and integrated circuits, as well as the future prospective and challenges are reviewed and discussed. The present study sets out to objectively measure the feasibility of the hybrid integration between Si photonics and 2D materials in on-chip optical communications and the advanced applications beyond.