Reduction of thermal effects in a 2.7-µm Er:Y2O3 ceramic laser with annular pumping.

Reduction of thermal effects is a challenging aspect for power scaling of 2.7-µm bulk Er-lasers due to the large quantum defect when pumping at ∼ 0.97 µm. Here, we demonstrate that thermal effects in an Er:Y2O3 ceramic laser can be significantly reduced pumping by an annular beam, thus improving the continuous-wave (CW) laser performance in the 3-µm spectral range. The excitation conditions of the TEM00 mode were determined theoretically by taking into account the propagation characteristics of the annular pump beam. For a comparison, the temperature and stress distributions are at first theoretically studied with three different pump configurations. In the experiment, output power of the Er:Y2O3 ceramic laser improved by ∼ 60% by changing the pump beam from coventional quasi-top-hat to a designed annular one. This work, as a proof-of-principle study, indicates the potential of power scaling of the 2.7-µm bulk Er-lasers pumping with an annular beam.

Sequencing and phylogenetic characterization of a novel RNA virus in Arma chinensis.

The complete genome of a novel virus from Arma chinensis was determined by RNA sequencing and rapid amplification of cDNA ends. This virus has a single-stranded RNA genome of 10,540 nucleotides (nt) excluding the poly(A) tail. Two non-overlapping open reading frames (ORFs) in the sense direction were predicted: one long ORF at the 5' end of the genome (6,219 nt) that encodes a polypeptide of 2,072 amino acids (aa), and one short ORF at the 3' end of the genome (3,033 nt) that encodes a polypeptide of 1,010 aa. Phylogenetic analysis indicated that the virus clusters within a large cluster of currently unidentified picorna-like viruses with a high bootstrap value. We named the virus isolate Arma chinensis picorna-like virus 1 (AcPV-1). The prevalence of AcPV-1 infection in samples of Arma chinensis from the wild was at a low level (5.48%, 8 positives in 146 samples). Keywords: Arma chinensis; genomic characterization; phylogenetic analysis; Arma chinensis picorna-like virus 1; prevalence.

A Two-Dimensional Ruddlesden-Popper Perovskite Nanowire Laser Array based on Ultrafast Light-Harvesting Quantum Wells.

Miniaturized nanowire nanolasers of 3D perovskites feature a high gain coefficient; however, room-temperature optical gain and nanowire lasers from 2D layered perovskites have not been reported to date. A biomimetic approach is presented to construct an artificial ligh-harvesting system in mixed multiple quantum wells (QWs) of 2D-RPPs of (BA)2 (FA)n-1 Pbn Br3n+1 , achieving room-temperature ASE and nanowire (NW) lasing. Owing to the improvement of flexible and deformable characteristics provided by organic BA cation layers, high-density large-area NW laser arrays were fabricated with high photostability. Well-controlled dimensions and uniform geometries enabled 2D-RPPs NWs functioning as high-quality Fabry-Perot (FP) lasers with almost identical optical modes, high quality (Q) factor (ca. 1800), and similarly low lasing thresholds.

Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with high luminescence and stability.

Zero-dimensional (0D) perovskite Cs4PbBr6 has been speculated to be an efficient solid-state emitter, exhibiting strong luminescense on achieving quantum confinement. Although several groups have reported strong green luminescence from Cs4PbBr6 powders and nanocrystals, doubts that the origin of luminescence comes from Cs4PbBr6 itself or CsPbBr3 impurities have been a point of controversy in recent investigations. Herein, we developed a facile one-step solution self-assembly method to synthesize pure zero-dimensional rhombohedral Cs4PbBr6 micro-disks (MDs) with a high PLQY of 52% ± 5% and photoluminescence full-width at half maximum (FWHM) of 16.8 nm. The obtained rhombohedral MDs were high quality single-crystalline as demonstrated by XRD and SAED patterns. We demonstrated that Cs4PbBr6 MDs and CsPbBr3 MDs were phase-separated from each other and the strong green emission comes from Cs4PbBr6. Power and temperature dependence spectra evidenced that the observed strong green luminescence of pure Cs4PbBr6 MDs originated from direct exciton recombination in the isolated octahedra with a large binding energy of 303.9 meV. Significantly, isolated PbBr64- octahedra separated by a Cs+ ion insert in the crystal lattice is beneficial to maintaining the structural stability, depicting superior thermal and anion exchange stability. Our study provides an efficient approach to obtain high quality single-crystalline Cs4PbBr6 MDs with highly efficient luminescence and stability for further optoelectronic applications.

Characterization of glutathione S-transferases in the detoxification of metolachlor in two maize cultivars of differing herbicide tolerance.

Glutathione S-transferases (GSTs) have been widely studied in relation to their role in herbicide tolerance and detoxification. However, a detailed characterization of GSTs from herbicide tolerant and sensitive maize cultivars is still lacking. In this study, we determined the mechanism of differential tolerance between two maize cultivars which had 4-fold difference tolerance to metolachlor. The metabolism rate of metolachlor was more rapid in the tolerant cultivar (Zea mays L. cv Nongda86) than the susceptible one (Zea mays L. cv Zhengda958). Addition of the GST inhibitor ethacrynic acid reduced the metabolism of metolachlor indicating the involvement of GSTs in the differential detoxification of metolachlor. The expression profiles of 32 GST isozymes were measured using quantitative RT-PCR. The results showed the expression of GST genes were slightly up-regulated in Nongda86, but severely inhibited in Zhengdan958 24h after metolachlor treatment. The genes GSTI, GSTIII, GSTIV, GST5, GST6 and GST7, which can detoxify chloroacetanilide herbicides, were all expressed higher in Nongda86 compared to Zhendgan958. The result of GST activity was consistent with the gene expression profiles. Collectively, higher-level expression of GST genes, leading to higher GST activity and faster herbicide detoxification, appears to be responsible for the difference in tolerance to metolachlor in two maize cultivars.

Colorimetric Signal Amplification Assay for Mercury Ions Based on the Catalysis of Gold Amalgam.

Mercury is a major threat to the environment and to human health. It is highly desirable to develop a user-friendly kit for on-site mercury detection. Such a method must be able to detect mercury below the threshold levels (10 nM) for drinking water defined by the U.S. Environmental Protection Agency. Herein, we for the first time reported catalytically active gold amalgam-based reaction between 4-nitrophenol and NaBH4 with colorimetric sensing function. We take advantage of the correlation between the catalytic properties and the surface area of gold amalgam, which is proportional to the amount of the gold nanoparticle (AuNP)-bound Hg(2+). As the concentration of Hg(2+) increases until the saturation of Hg onto the AuNPs, the catalytic performance of the gold amalgam is much stronger due to the formation of gold amalgam and the increase of the nanoparticle surface area, leading to the decrease of the reduction time of 4-nitrophenol for the color change. This sensing system exhibits excellent selectivity and ultrahigh sensitivity up to the 1.45 nM detection limit. The practical use of this system for Hg(2+) determination in tap water samples is also demonstrated successfully.

2D Ruddlesden-Popper Perovskites Microring Laser Array.

3D organic-inorganic hybrid perovskites have featured high gain coefficients through the electron-hole plasma stimulated emission mechanism, while their 2D counterparts of Ruddlesden-Popper perovskites (RPPs) exhibit strongly bound electron-hole pairs (excitons) at room temperature. High-performance solar cells and light-emitting diodes (LEDs) are reported based on 2D RPPs, whereas light-amplification devices remain largely unexplored. Here, it is demonstrated that ultrafast energy transfer along cascade quantum well (QW) structures in 2D RPPs concentrates photogenerated carriers on the lowest-bandgap QW state, at which population inversion can be readily established enabling room-temperature amplified spontaneous emission and lasing. Gain coefficients measured for 2D RPP thin-films (≈100 nm in thickness) are found about at least four times larger than those for their 3D counterparts. High-density large-area microring arrays of 2D RPPs are fabricated as whispering-gallery-mode lasers, which exhibit high quality factor (Q ≈ 2600), identical optical modes, and similarly low lasing thresholds, allowing them to be ignited simultaneously as a laser array. The findings reveal that 2D RPPs are excellent solution-processed gain materials potentially for achieving electrically driven lasers and ideally for on-chip integration of nanophotonics.

Composition-Graded Cesium Lead Halide Perovskite Nanowires with Tunable Dual-Color Lasing Performance.

Cesium lead halide (CsPbX3 ) perovskite has emerged as a promising low-threshold multicolor laser material; however, realizing wavelength-tunable lasing output from a single CsPbX3 nanostructure is still constrained by integrating different composition. Here, the direct synthesis of composition-graded CsPbBrx I3-x nanowires (NWs) is reported through vapor-phase epitaxial growth on mica. The graded composition along the NW, with an increased Br/I from the center to the ends, comes from desynchronized deposition of cesium lead halides and temperature-controlled anion-exchange reaction. The graded composition results in varied bandgaps along the NW, which induce a blueshifted emission from the center to the ends. As an efficient gain media, the nanowire exerts position-dependent lasing performance, with a different color at the ends and center respectively above the threshold. Meanwhile, dual-color lasing with a wavelength separation of 35 nm is activated simultaneously at a site with an intermediate composition. This position-dependent dual-color lasing from a single nanowire makes these metal halide perovskites promising for applications in nanoscale optical devices.