Watt-level continuous-wave antimonide laser diodes with high carrier-confined active region above 2.5 µm.

Thanks to high performance above room temperature, antimonide laser diodes have shown great potential for broad application in the mid-infrared spectral region. However, the laser`s performance noticeably deteriorates due to the reduction of carrier confinement with increased emission wavelength. In this paper, a novel active region with higher carrier confinements both of electron and hole, by the usage of an indirect bandgap material of Al0.5GaAs0.04Sb as the quantum barrier, was put up to address the poor carrier confinement of GaSb-based type-I multi-quantum-well (MQW) diode lasers emission wavelength above 2.5 µm. The carrier confinement and the differential gain in the designed active region are enhanced as a result of the first proposed usage of an indirect-gap semiconductor as the quantum barrier with larger band offsets in conduction and valence bands, leading to high internal quantum efficiency and low threshold current density of our lasers. More importantly, the watt-level output optical power is obtained at a low injection current compared to the state of the art. Our work demonstrates a direct and cost-effective solution to address the poor carrier confinement of the GaSb-based MQW lasers, thereby achieving high-power mid-infrared lasers.

Robust design of mid-infrared GaSb-based single-mode laser diode fabricated by standard photolithography with socketed ridge-waveguide modulation.

In this paper, we put up a robust design of a stable single-mode-operated GaSb-based laser diode emitting around 1950nm. This novel design structure with socketed ridge-waveguide enables a simple fabrication and batch production of mid-infrared laser diodes on account of the mere usage of standard photolithography. By introducing micron-level index perturbations distributed along the ridge waveguide, the threshold gains of different FP modes are modulated. Four geometrical parameters of the perturbations are systematically optimized by analyzing the reflection spectrum to get a robust single-mode characteristic. Based on the optimized geometrical parameters, 1-mm long uncoated lasers are carried out and exhibit a stable single longitudinal mode from 10 °C to 40 °C with a maximum output power of more than 10 mW. Thus, we prove the feasibility of the standard photolithography to manufacture the monolithic single-mode infrared laser source without regrowth process or nanoscale lithography.

Promotion of Specific Single-Transverse-Mode Beam Characteristics for GaSb-Based Narrow Ridge Waveguide Lasers via Customized Parameter Design.

GaSb-based single-transverse-mode narrow ridge waveguide (RW) lasers with high power and simultaneous good beam quality have broad application prospects in the mid-infrared wavelength region. Yet its design and formation have not been investigated systematically, while the beam characteristics that affect their suitability for specific applications remain rarely analyzed and optimized. The present work addresses these issues by theoretically establishing a waveguide parameter domain that generalizes the overall possible combinations of ridge widths and etch depths that support single-transverse-mode operation for GaSb-based RW lasers. These results are applied to develop two distinct and representative waveguide designs derived from two proposed major optimization routes of model gain expansion and index-guiding enhancement. The designs were evaluated experimentally based on prototype 1-mm cavity-length RW lasers in the 1950 nm wavelength range, which were fabricated with waveguides having perpendicular ridge and smooth side-walls realized through optimized dry etching conditions. The model gain expanded RW laser design with a relatively shallow-etched (i.e., 1.55 [Formula: see text]m) and wide ridge (i.e., 7 [Formula: see text]m) yielded the highest single-transverse-mode power to date of 258 mW with a narrow lateral divergence angle of 11.1[Formula: see text] full width at half maximum at 800 mA under room-temperature continuous-wave operation, which offers promising prospects in pumping and coupling applications. Meanwhile, the index-guiding enhanced RW laser design with a relatively deeply etched (i.e., 2.05 [Formula: see text]m) and narrow ridge (i.e., 4 [Formula: see text]m) provided a highly stable and nearly astigmatism-free fundamental mode emission with an excellent beam quality of M[Formula: see text] factor around 1.5 over the entire operating current range, which is preferable for seeding external cavity applications and complex optical systems.

Design and improve of the near-infrared phosphor by adjusting the energy levels or constructing new defects.

Ca3Ga2Ge4O14:Cr3+ phosphors with a broad emission band are prepared by the high temperature solid state method. The emission peak position of Ca3Ga(2-x)Ge4O14:Cr3+ is located at 745 nm. Considering that the biological detection needs a widely spectra matching with the first biological window (650 nm-900 nm), Al3+ and In3+ are introduced into the Ga3+ sites to tune the peak position. When the Ga3+ (0.62 Å) is substituted by smaller Al3+ (0.535 Å), the crystal field around Cr3+ is enhanced, the energy level 4T2(4F) will move up and overlap with 2E(2G) level. As a result, the emission peak of Cr3+shift from 745 nm to 730 nm with an enhancement in the intensity about 19 times due to the electro transfer from 2E(2G) level to 4T2(4F) level. However, the energy level 4T2(4F) will move down when the Ga3+ is replaced by the larger In3+ (0.8 Å), which leads to the red shift of the emission peak from 745 nm to 780 nm. Meanwhile, the intensity is enhanced about 17 times with constructing the defects. In summary, the wide emission spectra of these samples can be tuned from730nm to 780 nm continuously by controlling the concentration of Al3+ and In3+.

Reverse effect of Sm3+ on Ce3+ in Ca2BO3Cl:Ce3+/Tb3+/Sm3+ phosphor: Luminescence, energy transfer and occupation site.

A series of Ca2BO3Cl:Ce3+, Tb3+, Sm3+ are successfully synthesized by a high temperature solid state reaction. And the crystal structure, luminescence property and energy transfer mechanism of Ce3+/Sm3+, Tb3+/Sm3+ and Ce3+/Tb3+/Sm3+ in Ca2BO3Cl are investigated. There is an interesting phenomenon that the right side of the Ce3+ emission spectra in Ca2BO3Cl:Ce3+, Sm3+ compresses gradually with increasing the Sm3+ concentration. By means of refinement, it can be found that Sm3+ ions are mainly occupied in the Ca2 sites, because the cell of the Ca2 lattice is easily occupied. Then, the emission peak2 of Ce3+ in Ca2 sites occurs to blue shift. While the emission peak1 of Ce3+ in Ca1 sites is basically stability. However, the emission of Ce3+ in Ca2BO3Cl:Ce3+, Tb3+, Sm3+ have different changes with increasing the Sm3+ concentration that the emission peaks of Ce3+ shift to long wave at first then to short wave and the FWHM remains stability. This can be attributed to the existence of Tb3+. For the energy transfer mechanism, according to Dexter's energy transfer theory and Reisfeld's approximation, the energy transfer process of Ce3+/Sm3+ and Tb3+/Sm3+ should be the dipole-dipole interaction. And white emitting phosphor is achieved by the efficient energy transfer.

Diastereoselective Michael reaction of chiral nickel(II) glycinate with nitroalkenes for asymmetric synthesis of ß-substituted α,γ-diaminobutyric acid derivatives in water.

We have developed the first operationally simple and environmentally benign protocol for the aqueous asymmetric Michael addition reaction of chiral nickel(II) glycinate with nitroalkenes. The reactions proceeded smoothly in the presence of TBAB (tetrabutyl ammonium bromide) in neat water at room temperature and provided good yields of ß-substituted α,γ-diaminobutyric acid derivatives with excellent diastereoselectivities.

Differentiation of common diastereoisomeric ursane-type triterpenoids by high-performance liquid chromatography/tandem mass spectrometry.

A rapid and stable method consisting of high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry was established for the identification and differentiation of common diastereoisomeric ursane-type triterpenoids at the C-3 position. Two characteristic fragment ions, [M-H-H(2) O-CO(2)](-) and [M-H-H(2)O-HCOOH](-) , exhibited significant stereochemical effects and were utilized to distinguish 3-OH epimers. Based on reference standards, the abundance of the fragment ion [M-H-H(2)O-HCOOH](-) in 3ß-OH compounds in the MS(3) experiment was dramatically higher compared to [M-H-H(2) O-CO(2)](-); however, for 3α-OH compounds, the product ion [M-H-H(2) O-CO(2)](-) was noted to be higher than [M-H-H(2)O-HCOOH](-). Energy-resolved mass spectrometric experiments were carried out to support the differentiation of these diastereoisomeric triterpenoids at the C-3 position. Using this method, a total of nine ursane-type triterpenoids from a plant crude extract, including four pairs of epimers at the C-3 position, were identified and distinguished rapidly. Furthermore, offline Fourier transform ion cyclotron resonance tandem mass spectrometry was also performed to assign accurate elemental compositions.

Evaluation of the hepatoprotective and antioxidant activities of Rubus parvifolius L.

The hepatoprotective and antioxidant activities of the n-butanol extract of Rubus parvifolius L. (RPL), a widely used medicinal plant, were evaluated. Results demonstrated that RPL extract possessed pronounced hepatoprotective effects against carbon tetrachloride (CCl(4))-induced hepatic injury in mice, which was at least partially attributed to its strong antioxidant capacity. Treatment with RPL extract markedly attenuated the increases in serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels caused by CCl(4) intoxication. It also significantly prevented the decrease in superoxide dismutase (SOD) activity and the increase in malondialdehyde (MDA) content of liver tissue. Meanwhile, histopathological changes of hepatic damage were also remarkably ameliorated. Phytochemical analysis based on high-performance liquid chromatography/tandem mass spectrometry (HPLC-MS/MS) revealed the presence of various phenolic compounds, including caffeic acid conjugates, ellagic acid glycosides, and flavonol glycosides, which might be responsible for the hepatoprotective and antioxidant activities of RPL.

Discovery of novel purine derivatives with potent and selective inhibitory activity against c-Src tyrosine kinase.

We report here the discovery of novel purine derivatives with potent and selective inhibitory activity against c-Src tyrosine kinase by adopting a strategy integrating focused combinatorial library design, virtual screening, chemical synthesis, and bioassay. Thirty two compounds were selected and synthesized. All compounds showed potent inhibitory activity against c-Src kinase with IC50 values ranging from 3.14 µM to 0.02 µM. Compound 5i was identified as one of the most potent agent with an IC50 120 times lower than those of the hits. The high hit rate (100%) and the potency of the new Src kinase inhibitors demonstrated the efficiency of the strategy for the focused library design and virtual screening. The novel active chemical entities reported here should be good leads for further development of purine-based anticancer drugs targeting Src tyrosine kinase.

Highly alpha-selective synthesis of sialyl spirohydantoins by regiospecific domino condensation/O-->N acyl migration/N-sialylation of carbodiimides with peracetylated sialic acid.

A novel and efficient process for the synthesis of alpha-sialyl spirohydantoin analogues via one-pot sequential reaction involving various carbodiimides and peracetylated Neu5Ac is reported. BF(3) x Et(2)O mediating intramolecular N-sialylation with excellent alpha-selectivity is first demonstrated.

Single-step purification of dracorhodin from dragon's blood resin of Daemonorops draco using high-speed counter-current chromatography combined with pH modulation.

Dracorhodin is a major constituent found in "Dragon's blood" resin of Daemonorops draco Willd. Blume. This natural flavylium compound is a potent pharmaceutical substance due to its biological and pharmacological activities such as antimicrobial, antiviral, antitumor and cytotoxic activity. An effective high-speed counter-current chromatography method was successfully established for the isolation and purification of dracorhodin directly from extract of D. draco by using a two-phase solvent system composed of n-hexane/ethyl acetate/methanol/water (2:3:2:3 v/v). Under the optimal conditions, 6.6 mg dracorhodin was obtained from 100 mg crude resin. The isolated fraction of counter-current chromatography was determined by HPLC, NMR, UV/visible and ESI/MS combined with pH modulation, since dracorhodin is unstable in solution which exists in different forms depending on pH values. The data were compared with those of the reference substance, and the literatures as well. The purity of dracorhodin was over 98% based on the HPLC result.