The recently discovered novel properties of two dimensional materials largely rely on the layer-critical variation in their electronic structure and lattice symmetry. Achieving layer-by-layer precision patterning is thus crucial for junction fabrications and device engineering, which hitherto poses an unprecedented challenge. Here we demonstrate laser thinning and patterning with layer-by-layer precision in a two dimensional (2D) quantum material MoS2. Monolayer, bilayer and trilayer of MoS2 films are produced with precise vertical and lateral control, which removes the extruding barrier for fabricating novel three dimensional (3D) devices composed of diverse layers and patterns. By tuning the laser fluence and exposure time we demonstrate producing MoS2 patterns with designed layer numbers. The underlying physics mechanism is identified to be temperature-dependent evaporation of the MoS2 lattice, verified by our measurements and calculations. Our investigation paves way for 3D device fabrication based on 2D layered quantum materials.

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We report the near to middle infrared luminescence and energy transfer process of Er3+/Yb3+ co-doped fluorotellurite glasses under 980, 1550 and 800 nm excitations, respectively. Using a 980 nm laser diode pump, enhanced 1.5 and 2.7 μm emissions from Er3+:I13/2→4I15/2 and I11/2→4I13/2 transitions are observed, in which Yb3+ ions can increase pumping efficiency and be used as energy transfer donors. Meanwhile, Yb3+ can also be used as an acceptor and intensive upconversion luminescence of around 1000 nm is achieved from Er3+:I11/2→4I15/2 and Yb3+: F5/2→4F7/2 transitions using 1550 nm excitation. In addition, the luminescence properties and variation trendency by 800 nm excitation is similar to that using 1550 nm excitation. The optimum Er3+ and Yb3+ ion ratio is 1:1.5 and excess Yb3+ ions decrease energy transfer efficiency under the two pumpings. These results indicate that Er3+/Yb3+ co-doped fluorotellurite glasses are potential middle- infrared laser materials and may be used to increase the efficiency of the silicon solar cells.

AlF3-based glasses (AlF3-YF3-CaF2-BaF2-SrF2-MgF2) with enhanced thermal and chemical stability were synthesized and compared with the well-known fluorozirconate glass (ZBLAN). The 2.7 μm mid-infrared emission in the AlF3-based glasses was also investigated through the absorption and emission spectra. Both the temperature of glass transition and the characteristic temperatures (ΔT, Hr, kgl) of the fluoroaluminate glasses were much larger than those of the ZBLAN glasses. The corrosion phenomenon can be observed by naked-eye, and the transmittance dropped dramatically (0% at 3 μm) when the ZBLAN glass was placed into distilled water. However, the AlF3-based glass was relatively stable. The fluoroaluminate glasses possessed large branching ratio (20%) along with the emission cross section (9.4×10−21 cm−2) of the Er3+:4I11/2→4I13/2 transition. Meanwhile, the enhanced 2.7 μm emission in highly Er3+-doped AYF glass was obtained. Therefore, these results showed that this kind of fluoride glass has a promising application for solid state lasers at 3 μm.

Doping engineering has emerged as one of the most powerful approaches to impart new optical and electronic properties to halide perovskite nanocrystals (NCs). However, the impact of dopants on the structure of perovskite NCs remains poorly understood. Here, we report on the finding of dopinginduced structural phase transitions occurring in all-inorganic perovskite NCs. Using Ni 2+ -doped CsPbCl 3 NCs as a model system, we show that Ni 2+ doping causes the coexistence of dual subdomains of cubic and orthorhombic phases and inhibits the phase transition from cubic to orthorhombic in NCs with negligible atomic vacancies as the temperature decreases. Car− Parrinello molecular dynamics simulations reveal that the dopinginduced structural phase transition results from the dopantenabled release of lattice strain and a temperature-insensitive local structural change in the doped region of NCs. Since size mismatch between dopants and replaced ions widely exists in doped functional materials, our finding may not be limited to halide perovskite NCs, but could have implications even for other classes of doped NCs and bulk materials.

We report an unambiguous observation of third-order nonlinear optical effect, spatial self-phase modulation (SSPM), in a MoTe 2 dispersion. The values of the third order nonlinear optical coefficients effectively for one layer MoTe 2 , χ (3) one-layer , are obtained through the SSPM method at excitation wavelengths 473, 532, 750 and 801 nm, respectively. The wind-chime model is used to explain the ring formation time. The wavelength dependence of χ (3) one-layer compares well with the photo-absorption spectra. Significantly, we find a correlation between χ (3) and the carrier mobility μ or effective mass m * , which again further supports the laser-induced ac electron coherence in 2D materials.

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