No abstract

dynamic response, and large optical nonlinearity, graphene has been demonstrated to be a new nonlinear optical material for the generation and modulation of laser pulses, [ 4,5 ] which could fi nd important applications for telecommunications and optical sensing. However, the relative weak absorption in monolayer graphene (2.3% of incident light) gives a small absolute value (approximately 1%) of optical modulation depth, [ 6,7 ] which brings certain limitation for nonlinear photonics at specifi c wavelength. TMDs have a high resonant absorption up to >20%, [ 8,9 ] but the optical response mainly lies in visible range due to a moderate bandgap (1 eV for bulk and 2 eV for monolayer). [ 10 ] It is noteworthy that great technological demands for optical communications exist mainly in the infrared wavelength range around 1500 nm (0.8 eV). To this point, black phosphorus (BP), [ 11,12 ] a new member of the layered-material family with bandgap from 0.3 (bulk) to 1.5 eV (monolayer), [13][14][15] can bridge the gap between zero-gap graphene and relatively large bandgap TMDs for infrared photonics and optoelectronics.Because of the unique orthorhombic crystal structure, [ 16 ] BP shows tunable optical properties which are very sensitive to thickness, doping, and light polarization. [ 13,17,18 ] Unlike TMDs, Black phosphorus (BP) is a very promising material for telecommunication due to its direct bandgap and strong resonant absorption in near-infrared wavelength range. However, ultrafast nonlinear photonic applications relying on the ultrafast photocarrier dynamics as well as optical nonlinearity in black phosphorus remain unexplored. In this work, nonlinear optical properties of solution exfoliated BP are investigated and the usage of BP as a new saturable absorber for high energy pulse generation in fi ber laser is demonstrated. In order to avoid the oxidization and degradation, BP is encapsulated by polymer matrix which is optically transparent in the spectrum range of interest to form a composite. Two fabrication approaches are demonstrated to produce BP-polymer composite fi lms which are further incorporated into fi ber laser cavity as nonlinear media. BP shows very fast carrier dynamics and BP-polymer composite has a modulation depth of 10.6%. A highly stable Q-switched pulse generation is achieved and the single pulse energy of 194 nJ is demonstrated. The ease of handling of such black phosphorus-polymer composite thin fi lms affords new opportunities for wider applications such as optical sensing, signal processing, and light modulation.

The antimicrobial activity and mechanism of CdTe quantum dots (QDs) against Escherichia coli were investigated in this report. Colony-forming capability assay and atomic force microscopy (AFM) images show that the QDs can effectively kill the bacteria in a concentration-dependent manner. Results of photoluminescence spectrophotometry, confocal microscopy, and antioxidative response tests indicate that the QDs bind with bacteria and impair the functions of a cell's antioxidative system, including down-regulations of antioxidative genes and decreases of antioxidative enzymes activities. The oxidative damage of protein and lipid is also observed with thiobarbituric reacting substances and protein carbonyl assays, respectively. On the basis of these results, it is proposed that the mechanism of the antimicrobial activity of CdTe QDs involves QDs-bacteria association and a reactive oxygen species-mediated pathway. Thus, CdTe QDs could have the potential to be formulated as a novel antimicrobial material with excellent optical properties.