Multiexciton dynamics in CsPbBr3nanocrystals: the dependence on pump fluence and temperature.

Multiexcitons generation is a process of generating electron-hole pairs in nanostructured semiconductors by absorbing a single high-energy photon. The multiexciton process is essential for the performance of optoelectronic devices based on perovskite nanomaterials. In this paper, ultrafast time-resolved transient absorption spectroscopy is used to study the ultrafast dynamics of CsPbBr3nanocrystals. It is found that the multiexcitons Auger recombination lifetime increases with the decrease of pump fluence, while it is on the contrary for the hot carrier cooling time. The increase in the number of photons absorbed by each nanocrystal under high pump fluence slows down the relaxation of hot carriers to the band edge. The hot carrier cooling lifetime increases from 0.25 to 0.85 ps when the pump fluence increases from 6 to 127µJ cm-2. Temperature-dependent transient absorption spectroscopy exhibits that the relaxation process of hot carriers slows down sharply when the lattice temperature decreases from 280 to 80 K. Moreover, the exciton binding energy 46 meV of CsPbBr3nanocrystals is obtained by temperature-dependent steady-state photoluminescence spectroscopy. These findings provide insights for applications such as solar cells and light-emitting devices based on CsPbBr3nanocrystals.

Bactericidal effects of hematoporphyrin monomethyl ether-mediated blue-light photodynamic therapy against Staphylococcus aureus.

The implementation of photodynamic therapy (PDT) usually uses red light as the excitation source to obtain a deeper penetration depth. However, for some superficial infectious diseases, using red-light PDT may damage the normal tissues underneath. If we choose a shorter wavelength light, then the effect of PDT can be limited to the superficial region. This study assessed the effect of blue-light PDT against Staphylococcus aureus. The absorption of hematoporphyrin monomethyl ether (HMME) by S. aureus was investigated using fluorescence spectroscopy. The bactericidal effects of HMME, light alone, and PDT using blue light (405 nm) on S. aureus were studied. The results indicate that the HMME uptake by S. aureus rapidly reached a certain value, then steadily increased with time in the range of 0-80 min, and thenreached a plateau at 80 min before a slow decline afterward. Without light irradiation, less than 2 µg ml-1 HMME showed no bactericidal effect on S. aureus. Without HMME, blue-light at a power density of 20 mW cm-2 had no significant bactericidal effect for 0.5 min to 10 min. When 2 µg ml-1 of HMME was combined with blue-light (20 mW cm-2), the bactericidal effect showed a reduction of 3 log10 with the extension of irradiation time. These results demonstrated that bacteria have the ability to absorb HMME, and HMME-mediated blue-light PDT can effectively kill the bacteria, which laid the foundation for blue-light PDT as a non-invasive treatment for superficial infectious diseases.

Optimization for vertically scanning terahertz attenuated total reflection imaging.

Terahertz attenuated total reflection imaging has been used to develop preliminary applications without any in-depth analysis of the nature of present systems. Based on our proposed vertically scanning imaging system, an analysis of optimum prism design and polarization selection for error reduction is presented theoretically and experimentally, showing good agreement. By taking the secondary reflection inside the prism and the prism deflection into consideration, p-polarized terahertz waves are recommended for prisms with a base angle below 31°, leading to minimum error. This work will contribute to the development of more practical application of terahertz attenuated total reflection scanning imaging in various fields with enhanced performance.

[Prenatal ultrasonic manifestation and clinical significance of fetal hemivertebra].

OBJECTIVE: To explore the manifestation and clinical significance of prenatal ultrasound diagnosis of fetal hemivertebra. METHODS: In the study, 27 fetals with hemivertebras (proven by post-natal X-ray, CT or MR) were examined by prenatal ultrasound and MR in Women & Children's Hospital, Ningbo, Zhejiang. Two-dimensional and three-dimensional prenatal ultrasonic manifestations were retrospective analyzed and compared with the prenatal MR diagnoses, the post-natal X-ray, CT, MR examinations. All the fetuses were carried out karyotype examinations. The full-term births recieved surgical treatment and the Cobb angle correction rate was calculated. RESULTS: The 27 cases of fetal ultrasound showed the morphological changes of the spine, with the involved segment only half of the vertebra, in which 9 cases were single hemivertebra and 18 cases multiple, 8 cases were no malformation and 19 cases other malformations, and 19 cases were induction of labor, and 8 cases of term delivery. Compared with postpartum X-ray and other imaging tests, the prenatal ultrasound accuracy rate was 92.5%, and prenatal MR 96.3%. In the 27 cases, the chromosome cultures of 25 cases were successful, in which the normal karyotype was 68.0% (17/25), and abnormal karyotype 32.0% (8/25) with multiple hemivertebra accounting for 47.1% (8/17). In 8 cases with posterior approach of hemivertebra resection, 6 patients were less than and equal to 3 years old, whose average Cobb angle correction rate was 38.02%, and 2 more than 3 years old, whose average Cobb angle correction rate was 24.98%. CONCLUSION: Fetal hemivertebra have typical sonographic manifestations. In diagnosis of fetal hemivertebra, the accuracy of prenatal ultrasound is close to that of MR, which has important clinical implications in diagnosis and overall assessment of fetal hemivertebra, and can also provide appropriate clinical genetic reference.

Transient Absorption Spectroscopy of a Carbazole-Based Room-Temperature Phosphorescent Molecule: Real-Time Monitoring of Singlet-Triplet Transitions.

Real-time monitoring of singlet-triplet transitions is an effective tool for studying room-temperature phosphorescent molecules. For femtosecond transient absorption (TA) spectroscopy of a 2,6-di(9H-carbazol-9-yl) pyridine molecule in dimethyl sulfoxide (DMSO), the stimulated emission signal (380 nm) and the excited-state absorption signal (650 nm) reach their maximum intensity within 397 fs. Subsequently, the two signals decay with time and the triplet-triplet absorption (TTA) signal (400 nm) is enhanced synchronously, accompanied by an isosbestic point at 491 nm. These results confirm intersystem crossing (ISC) within 2.5 ns. Moreover, the TTA signal (400 nm) in nanosecond TA spectroscopy gradually disappeared, accompanied by a phosphorescence lifetime of 4.1 µs. As the solvent polarity decreases (DMSO > N,N-dimethylformamide > 1,4-dioxane > toluene), similar spectral dynamic processes are observed, while the durations of ISC processes and phosphorescence lifetimes are shortened. This combined femtosecond and nanosecond transient absorption spectroscopy study presents the ultrafast excited-state dynamics of organic phosphorescent molecules.

Excitation Wavelength and Intensity-Dependent Multiexciton Dynamics in CsPbBr3 Nanocrystals.

CsPbBr3 has attracted great attention due to unique optical properties. The understanding of the multiexciton process is crucial for improving the performance of the photoelectric devices based on CsPbBr3 nanocrystals. In this paper, the ultrafast dynamics of CsPbBr3 nanocrystals is investigated by using femtosecond transient absorption spectroscopy. It is found that Auger recombination lifetime increases with the decrease of the excitation intensity, while the trend is opposite for the hot-exciton cooling time. The time of the hot-carriers cooling to the band edge is increased when the excitation energy is increased from 2.82 eV (440 nm) to 3.82 eV (325 nm). The lifetime of the Auger recombination reaches the value of 126 ps with the excitation wavelength of 440 nm. The recombination lifetime of the single exciton is about 7 ns in CsPbBr3 nanocrystals determined by nanosecond time-resolved photoluminescence spectroscopy. The exciton binding energy is 44 meV for CsPbBr3 nanocrystals measured by the temperature-dependent steady-state photoluminescence spectroscopy. These findings provide a favorable insight into applications such as solar cells and light-emitting devices based on CsPbBr3 nanocrystals.

High-Efficiency Thickness-Insensitive Organic Solar Cells with an Insulating Polymer.

Achieving high-efficiency thick-film bulk heterojunction (BHJ) organic solar cells (OSCs) with thickness-independent power conversion efficiencies (PCEs) in a wide thickness range is still a challenge for the roll-to-roll printing techniques. The concept of diluting the transport sites within BHJ films with insulating polymers can effectively eliminate charge trapping states and optimize the charge transport. Herein, we first adopted the concept with insulating polypropylene (PP) in the efficient non-fullerene system (PM6:Y6) and demonstrated its potential to fabricate thick-film OSCs. The PP can form an insulating matrix prior to PM6 and Y6 within the BHJ film, resulting in an enhanced molecular interaction and isolated charge transport by expelling Y6 molecules. We thus observed reduced trap state density and improved charge transport properties in the PP-blended device. At around 300 nm, the PM6:Y6:PP device enjoys a high PCE of 15.5% and achieves over 100% of the efficiency of the optimal thin-film device, which is significantly improved compared to the binary PM6:Y6 counterpart. This research promotes an effective strategy with insulating polymers and provides knowledge of commercial production with response to the roll-to-roll technique demands.

The penetration effect of HMME-mediated low-frequency and low-intensity ultrasound against the Staphylococcus aureus bacterial biofilm.

BACKGROUND: The purpose of this study was to observe the effect of hematoporphyrin monomethyl ether (HMME)-mediated low-frequency and low-intensity ultrasound on mature and stable Staphylococcus aureus (S. aureus) biofilms under different ultrasound parameters. METHODS: The biofilm was formed after 48-h culture with stable concentration of bacterial solution. Different types of ultrasound and time were applied to the biofilm, and the ultrasonic type and time of our experiments were determined when the biofilm was not damaged. The penetration effects of low-frequency and low-intensity ultrasound were decided by the amount of HMME that penetrated into the biofilm which was determined by fluorescence spectrometry. RESULTS: The destruction of biofilms by pulse waveform was the strongest. Sinusoidal low-frequency and low-intensity ultrasound can enhance the biofilm permeability. For a period of time after the ultrasound was applied, the biofilm permeability increased, however, changes faded away over time. CONCLUSIONS: Low-frequency and low-intensity sinusoidal ultrasound significantly increased the permeability of the biofilms, which was positively correlated with the time and the intensity of ultrasound. Simultaneous action of ultrasound and HMME was the most effective way to increase the permeability of the biofilms.

Study of the dielectric characteristics of living glial-like cells using terahertz ATR spectroscopy.

The attenuated total reflection spectroscopy system with the Si container attached on the prism has been demonstrated as an efficient technique to obtain the dielectric properties of living cells in the THz range. We proposed a method to determine the dielectric responses of living cells based on the combination of the single-interface and two-interface ATR models without cell thickness. The experimental results for living glial-like cells (PC12, SVG P12 and HMO6) showed the dielectric responses in the THz region were related significantly to cell number, intracellular fluid, and cell structure. Moreover, the glioma cells (C6 and U87) exhibited different dielectric properties compared with the glial-like cells, which could be one reason for the glioma tissue diagnosis using THz wave.

Study of in vivo brain glioma in a mouse model using continuous-wave terahertz reflection imaging.

We demonstrated that in vivo brain glioma in a mouse model using a continuous-wave terahertz reflection imaging system, as well as the ex vivo fresh brain tissues in mouse model. The tumor regions of in vivo and ex vivo brain tissues can be well distinguished by THz intensity imaging at the frequency of 2.52THz. The THz images with high sensitivity correlated well with magnetic resonance, visual and hematoxylin and eosin stained images. Furthermore, the THz spectral difference between brain gliomas and normal brain tissues were obtained in the 0.6THz to 2.8THz range, where brain gliomas have the higher refractive indices and absorption coefficients, and their differences increase particularly in the high frequency range. These results suggest that THz imaging has great potential as an alternative method for the intraoperative label-free diagnosis of brain glioma in vivo.

[Clinical research of HPV DNA detection and HPV RNA detection in single time].

OBJECTIVE: To research the application of the single time detection of HPV E6/E7 mRNA and HC2-HPV-DNA in cervical screening project. METHODS: We detected both HPV E6/E7 mRNA and HC2-HPV-DNA of each sample which collected from 130 cervical disease patients' cervix during Jan. 2008 and July. 2009. TCT results were taken as standard to evaluate the diagnostic accuracy of the above two test methods in detecting high-grade cervical disease. RESULTS: 82.3% (107/130)women were confirmed to infect HPV by HC2-HPV-DNA detection, and 40.0% (52/130) women were confirmed to infect HPV by HPV E6/E7 mRNA detection, there was no significant difference between the two results (chi2 = 24.5, P < 0.05). The sensitivity, specificity, positive predictive value, negative predictive value of HC2-HPV-DNA detection were 90.1%, 22.1%, 37.4% and 82.6%, respectively. The sensitivity, specificity, positive predictive value, negative predictive value of HPV E6/E7 mRNA detection were 65.9%, 73.3%, 55.8% and 80.8%, respectively. CONCLUSION: In clinical cervical screening project of single time, the combination of HC2-HPV-DNA detection and HPV E6/E7 mRNA detection wick take on more potential value than applying each of them alone. RNA;

[Transnasal-sphenoided endosurgical and microsurgical technique of pituitary adenometomies].

OBJECTIVE: To evaluate the surgical technique of pituitary adenomas by naso-sphenoid way and the prevention of complication. METHOD: The pituitary adenomas in 19 cases were removed under endoscope and microscope by the transnasosphenoided way. Sphenoid-saddle base was restructed with lip-tendon-membrane and the nasal separate bone. RESULT: Seventeen cases had entire resection in the 19 patients. Two cases had subtotal resection. The symptoms were improved with no sever complications in 19 cases during the period of 3-36 months follow-up and no recovery in 17 cases. CONCLUSION: lt is a effective surgical technique that the pituitary neoplasms are removed by nasosphenoidal way under the endoscope and microscope with the alcohol for preventing the tumor recovery and with the lip-tendon-membrane and nasal separate bone for restructing the saddle base.