Black phosphorus quantum dots (BPQDs) were synthesized using a liquid exfoliation method that combined probe sonication and bath sonication. With a lateral size of approximately 2.6 nm and a thickness of about 1.5 nm, the ultrasmall BPQDs exhibited an excellent NIR photothermal performance with a large extinction coefficient of 14.8 L g(-1) cm(-1) at 808 nm, a photothermal conversion efficiency of 28.4%, as well as good photostability. After PEG conjugation, the BPQDs showed enhanced stability in physiological medium, and there was no observable toxicity to different types of cells. NIR photoexcitation of the BPQDs in the presence of C6 and MCF7 cancer cells led to significant cell death, suggesting that the nanoparticles have large potential as photothermal agents.

Although phosphorene has attracted much attention in electronics and optoelectronics as a new type of two‐dimensional material, in‐depth investigations and applications have been limited by the current synthesis techniques. Herein, a basic N‐methyl‐2‐pyrrolidone (NMP) liquid exfoliation method is described to produce phosphorene with excellent water stability, controllable size and layer number, as well as in high yield. Phosphorene samples composed of one to four layers exhibit layer‐dependent Raman scattering characteristics thus providing a fast and efficient means for the in situ determination of the thickness (layer number) of phosphorene. The linear and nonlinear ultrafast absorption behavior of the as‐exfoliated phosphorene is investigated systematically by UV–vis–NIR absorption and Z‐scan measurements. By taking advantage of their unique nonlinear absorption, ultrashort pulse generation applicable to optical saturable absorbers is demonstrated. In addition to a unique fabrication technique, our work also reveals the large potential of phosphorene in ultrafast photonics.

Black phosphorus (BP), an emerging narrow direct band-gap two-dimensional (2D) layered material that can fill the gap between the semi-metallic graphene and the wide-bandgap transition metal dichalcogenides (TMDs), had been experimentally found to exhibit the saturation of optical absorption if under strong light illumination. By taking advantage of this saturable absorption property, we could fabricate a new type of optical saturable absorber (SA) based on mechanically exfoliated BPs, and further demonstrate the applications for ultra-fast laser photonics. Based on the balanced synchronous twin-detector measurement method, we have characterized the saturable absorption property of the fabricated BP-SAs at the telecommunication band. By incorporating the BP-based SAs device into the all-fiber Erbium-doped fiber laser cavities, we are able to obtain either the passive Q-switching (with maximum pulse energy of 94.3 nJ) or the passive mode-locking operation (with pulse duration down to 946 fs). Our results show that BP could also be developed as an effective SA for pulsed fiber or solid-state lasers.

Black phosphorous (BP), the most thermodynamically stable allotrope of phosphorus, is a high-mobility layered semiconductor with direct band-gap determined by the number of layers from 0.3 eV (bulk) to 2.0 eV (single layer). Therefore, BP is considered as a natural candidate for broadband optical applications, particularly in the infrared (IR) and mid-IR part of the spectrum. The strong light-matter interaction, narrow direct band-gap, and wide range of tunable optical response make BP as a promising nonlinear optical material, particularly with great potentials for infrared and mid-infrared opto-electronics. Herein, we experimentally verified its broadband and enhanced saturable absorption of multi-layer BP (with a thickness of ~10 nm) by wide-band Z-scan measurement technique, and anticipated that multi-layer BPs could be developed as another new type of two-dimensional saturable absorber with operation bandwidth ranging from the visible (400 nm) towards mid-IR (at least 1930 nm). Our results might suggest that ultra-thin multi-layer BP films could be potentially developed as broadband ultra-fast photonics devices, such as passive Q-switcher, mode-locker, optical switcher etc.

Nonlayered materials are constructed with chemical covalent bonds in all three dimensions, distinct from layered materials, which contain evident structural differences in the horizontal and vertical directions. As a consequence, liquid‐phase exfoliation (LPE), a widely explored technique to obtain 2D layered nanoarchitectures, has not yet been fully characterized for the realization of 2D nonlayered nanostructures. Herein, by virtue of a typical chain‐like structure of crystalline bulk Te with strong TeTe covalent bonds in intrachains and weak Van der Waals forces in interchains, ultrathin 2D nonlayered Te nanosheets are realized by means of an LPE method. The resultant 2D Te nanosheets possess a broad lateral dimension ranging from 41.5 to 177.5 nm and a thickness ranging from 5.1 to 6.4 nm, and its photoresponse properties are evaluated using photoelectrochemical measurements. The 2D Te nanosheets exhibit excellent photoresponse behaviors from the UV to the visible regime in association with strong time and cycle stability for the on/off switching behaviors. The fabrication approach of 2D Te nanosheets would arouse interest in exfoliating other nonlayered 2D materials, which would expand the family of 2D materials.