Trion dynamics and charge photogeneration in MoS2 nanosheets prepared by liquid phase exfoliation.

Since excitonic quasiparticles, including excitons, trions and charges, have a great influence on the photoelectric characteristics of two-dimensional (2D) transition metal dichalcogenides (TMDs), systematic explorations of the trion dynamics and charge photogeneration in 2D TMDs are important for their future optoelectronic applications. Here, broadband femtosecond transient absorption spectroscopic experiments are performed first to investigate the peak shifting and broadening kinetics in MoS2 nanosheets in solution prepared by liquid phase exfoliation (LPE-MoS2, ∼9 layers, 9L), which reveal that the binding energies for the A-, B-, and C-exciton states are ∼77 meV, ∼76 meV, and -70 meV (the energy difference between free charges and excitons; the negative sign for C-excitons means a spontaneous dissociation nature in band-nesting regions), respectively. Then, the trion dynamics and charge photogeneration in LPE-MoS2 nanosheets have been studied in detail, demonstrating that they are comparable to those in chemical vapor deposition grown MoS2 films (1L-, 3L- and 7L-MoS2). These experimental results suggest that LPE-TMD nanosheets also have the potential for use in charge-related optoelectronic devices based on 2D TMDs.

Many-particle induced band renormalization processes in few- and mono-layer MoS2.

Band renormalization effects play a significant role for two-dimensional (2D) materials in designing a device structure and customizing their optoelectronic performance. However, the intrinsic physical mechanism about the influence of these effects cannot be revealed by general steady-state studies. Here, band renormalization effects in organic superacid treated monolayer MoS2, untreated monolayer MoS2and few-layer MoS2are quantitatively analyzed by using broadband femtosecond transient absorption spectroscopy. In comparison with the untreated monolayer, organic superacid treated monolayer MoS2maintains a direct bandgap structure with two thirds of carriers populated at K valley, even when the initial exciton density is as high as 2.05 × 1014cm-2(under 400 nm excitations). While for untreated monolayer and few-layer MoS2, many-particle induced band renormalizations lead to a stronger imbalance for the carrier population between K and Q valleys inkspace, and the former experiences a direct-to-indirect bandgap transition when the initial exciton density exceeds 5.0 × 1013cm-2(under 400 nm excitations). Those many-particle induced band renormalization processes further suggest a band-structure-controlling method in practical 2D devices.

Investigating the dynamics of excitons in monolayer WSe2 before and after organic super acid treatment.

Due to the large photoluminescence quantum yield, high mobility and good stability, organic super acid treated two-dimensional WSe2 has drawn much attention. However, reports about the influence of organic super acid treatment on the dynamic processes of excitons of monolayer WSe2 are still rare. In this work, through the broadband transient absorption spectra obtained using a femtosecond pump-probe system, we determine the dynamics of A' and C excitons in monolayer and bulk WSe2 at room temperature. Besides this, we also observe the relaxation process of the holes between the two spin split states in the valence band maximum in organic super acid treated monolayer WSe2. We find that the organic super acid treatment on monolayer WSe2 does not change the peak positions of the exciton states, while those bleaching peaks' intensities increase significantly due to the enhancement of oscillator strength for exciton states, corresponding to stronger steady-state photoluminescence. This could be attributed to the strain release induced by the defect repairing effect during the organic super acid treatment process.

Photoluminescence quenching of inorganic cesium lead halides perovskite quantum dots (CsPbX3) by electron/hole acceptor.

Recently, all-inorganic cesium lead halide perovskites (CsPbX3) quantum dots (QDs) have attracted great attention due to their halogen composition and size tunable band gap engineering, the same physical mechanism that is responsible for excellent performance in light-emitting devices. However, little is known about the time-resolved fluorescence quenching dynamics process of these CsPbX3 QDs. In this article, we present comprehensive contrastive spectral studies on the electron and hole extraction dynamics of CsPbX3 colloidal QDs with and without quencher by time-resolved femtosecond transient absorption (TA) and time-correlated single-photon counting (TCSPC) spectroscopy methods. We have identified that the partial electrons of the conduction band and holes of the valence band of CsPbX3 QDs can be directly extracted by tetracyanoethylene (TCNE) and phenothiazine (PTZ), respectively. Moreover, compared with the CsPbBr3 QDs, the CsPbI3 QDs showed relatively slower charge extraction rates. We also found that the CsPbBr3 QDs with smaller size showed faster carrier recombination rates and photoluminescence (PL) decay lifetime due to the relatively stronger quantum confinement effects. We believe that this study may be useful for realising optimal applications in photovoltaic and light emission devices.

Supersensitive and selective detection of picric acid explosive by fluorescent Ag nanoclusters.

Picric acid (PA) explosive is a hazard to public safety and health, so the sensitive and selective detection of PA is very important. In the present work, polyethyleneimine stabilized Ag nanoclusters were successfully used for the sensitive and selective quantification of PA on the basis of fluorescence quenching. The quenching efficiency of Ag nanoclusters is proportional to the concentration of PA and the logarithm of PA concentration over two different concentration ranges (1.0 nM-1 µM for the former and 0.25-20 µM for the latter), thus the proposed quantitative strategy for PA provides a wide linear range of 1.0 nM-20 µM. The detection limit based on 3σ/K is 0.1 nM. The quenching mechanism of Ag nanoclusters by PA is discussed in detail. The results indicate that the selective detection of PA over other nitroaromatics including 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (2,4-DNT), p-nitrotoluene (p-NT), m-dinitrobenzene (m-DNB), and nitrobenzene (NB), is due to the electron transfer and energy transfer between PA and polyethyleneimine-capped Ag nanoclusters. In addition, the experimental data obtained for the analysis of artificial samples show that the proposed PA sensor is potentially applicable in the determination of trace PA explosive in real samples.

[Effect of heme oxygenase on apoptosis and apoptosis genes in hepatic ischemia reperfusion injury in rats].

OBJECTIVE: To use heme oxygenase (HO) inducer hemin and a HO inhibitor zinc protoporphyrin (ZnPP) to investigate the effect of HO on apoptosis and apoptosis genes in hepatic ischemia reperfusion (IR) injury in rats. METHODS: Ninety-six Sprague-Dawley rats were randomly divided into four groups (24 rats in each): a sham-operation group, an ischemia-reperfusion (IR) group, a hemin-IR group and a ZnPP-IR group. Liver functions, liver histology and hepatocellular apoptosis rates were observed at 0, 1.5, 4 and 8 hours after reperfusion. Hepatocellular apoptosis was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling; expressions of Bcl-2 and caspase-3 were determined by Western blot. RESULTS: Compared with the sham-operation group, the levels of ALT and AST were increased in the IR group. In the IR group the histological changes found in the livers were swelling of hepatocytes, narrowing of hepatic sinusoids, inflammatory cell infiltration and necrosis of hepatocytes in some areas of the livers. In the IR group rate of hepatocellular apoptosis was increased at 0, 1.5, 4 and 8 hours after reperfusion; expression of Bcl-2 was decreased and the expression of caspase-3 was increased. In the hemin-IR group, the levels of ALT and AST were lower, the pathological changes were milder and the rate of hepatocellular apoptosis was lower at 0, 1.5, 4 and 8 hours in comparison to those of the IR group. The expression of Bcl-2 was higher and the expression of caspase-3 was lower in the hemin-IR group in comparison to those of the IR group. The results in the ZnPP-IR group were just the opposite to those of the hemin-IR group. CONCLUSION: HO might play a protective role in hepatic IR injury in rats, and this effect may be related to the inhibition of hepatocellular apoptosis.

[Cloning, expression and characterization of antibacterial peptide CM4 in Pichia pastoris].

To explore a new approach of expression of ABP-CM4 in methylotrophic yeast P. pastoris. The gene of ABP-CM4 was cloned into the vector pPIC9. The Sac I -linearized plasmid pPIC9-CM4 was transformed into P. pastoris GS115 by electroporation. By means of MM and MD plates and PCR, the recombinant P. pastoris strains (his- mut+) were obtained. Antibacterial assay, Tricine-SDS-PAGE and Polyarylamide Gel Electrophoresis demonstrated that ABP-CM4 was extracellularly expressed in P. pastoris with the induction of methanol. The recombinant ABP-CM4 has the antifungal activity on Aspergillus niger and Trichoderma viride.