Peizhuan Chen

Efficient two-photon absorption of CdSe-CdS/ZnS core-multishell quantum dots under the excitation of near-infrared femtosecond pulsed laser

We report that two-photon absorption (TPA) properties of semiconductor CdSe-core CdS/ZnS-multishell quantum dots (QDs) in toluene under excitation of femtosecond laser at 800 nm. The results show efficient TPA process and large TPA cross section of three types of size QDs, which is 1900, 5710, and 16060 GM (1 GM = 10−50 cm4 s photon−1), respectively. TPA cross section dramatically increases with increased core size, showing a strong size-dependence effect. Furthermore, two-photon excitation (TPE) fluorescence intensity not only depends on TPA capacity, but also relies on improved quantum yield resulting from passivation of QD surface by different coated monolayers (MLs). These facts in combination with the narrow fluorescence bandwidth make these QDs as promising probes for multicolor two-photon microscopy.

Design of semiconductor CdSe core ZnS∕CdS multishell quantum dots for multiphoton applications

Optical properties of colloidal II-VI semiconductor CdSe cores with ZnS and CdS multishell quantum dots (QDs) have been studied by experimental characterization and theoretical analysis. Due to the ...

An efficient light trapping scheme based on textured conductive photonic crystal back reflector for performance improvement of amorphous silicon solar cells

An efficient light trapping scheme named as textured conductive photonic crystal (TCPC) has been proposed and then applied as a back-reflector (BR) in n-i-p hydrogenated amorphous silicon (a-Si:H) solar cell. This TCPC BR combined a flat one-dimensional photonic crystal and a randomly textured surface of chemically etched ZnO:Al. Total efficiency enhancement was obtained thanks to the sufficient conductivity, high reflectivity and strong light scattering of the TCPC BR. Unwanted intrinsic losses of surface plasmon modes are avoided. An initial efficiency of 9.66% for a-Si:H solar cell was obtained with short-circuit current density of 14.74 mA/cm2, fill factor of 70.3%, and open-circuit voltage of 0.932 V.

Optimal design of one-dimensional photonic crystal back reflectors for thin-film silicon solar cells

For thin-film silicon solar cells (TFSC), a one-dimensional photonic crystal (1D PC) is a good back reflector (BR) because it increases the total internal reflection at the back surface. We used the plane-wave expansion method and the finite difference time domain (FDTD) algorithm to simulate and analyze the photonic bandgap (PBG), the reflection and the absorption properties of a 1D PC and to further explore the optimal 1D PC design for use in hydrogenated amorphous silicon (a-Si:H) solar cells. With identified refractive index contrast and period thickness, we found that the PBG and the reflection of a 1D PC are strongly influenced by the contrast in bilayer thickness. Additionally, light coupled to the top three periods of the 1D PC and was absorbed if one of the bilayers was absorptive. By decreasing the thickness contrast of the absorptive layer relative to the non-absorptive layer, an average reflectivity of 96.7% was achieved for a 1D PC alternatively stacked with a-Si:H and SiO2 in five periods. T...

Relations between reactive oxygen species and Raman spectral variations of human umbilical cord mesenchymal stem cells with different viability

In this study, the Reactive Oxygen Species (ROS) levels in Human Umbilical Cord Mesenchymal Stem Cells (hUC-MSCs) with different cell viability were measured by ROS probe fluorescence. It is found that the change of the ROS level with time (viability, decline) can be described by a Rational Function, whose integration can calculate the relative yield variations of ROS in different durations. The relative intensity variations of the characteristic Raman peak at 1342, 877, and 744 cm−1 were observed using Raman micro-spectroscopy. The results show that the relative yield variation of ROS and the relative intensity variations of the three Raman peaks can be described by a same model function (with different fitting parameter values). And the correlations between the relative intensity variations of the three Raman peaks and the relative yield variation of ROS were estimated by correlation coefficient method. It is found that they have perfect linear correlation coefficients of 0.980, 0.985, and 0.973, respectively. The analysis demonstrates that the intracellular excessive ROS can lead to the almost linear variation of the relative Raman peak intensity in hUC-MSCs with different viability.

Two-photon properties of CdSe core ZnS/CdS multishell quantum dots for bioimaging applications

This letter demonstrates that the fluorescence intensity of CdSe-core CdS/ZnS-multishell quantum dots (QDs) in toluene is related via a power-law of ~1.9 to the input intensity of femtosecond laser at 5~130 GW/cm2. This clearly indicates a broad range of optical intensity of two-photon excitation (TPE). The two-photon absorption (TPA) cross sections of QDs of core-size 2.9, 4.0 and 5.3 nm at 800 nm are 1980, 5680 and 14600 GM, respectively. Furthermore, the log-log plot of CdSe-core diameters versus the TPA cross sections shows the increase with a slope >3, indicating a nonlinear dependent relationship between TPA cross section and size of CdSe-core. The broad optical range of TPE and large TPA cross section make these QDs excellent candidates for two-photon fluorescent microscopy and bioimaging. Based on these two-photon properties of our QDs, we continue to investigate the bioimaging applications with two-photon microscopy. The results of the fluorescence images of living cells with the QDs demonstrate that QDs could be penetrate into cell membrane, then steadily and dispersedly distribute at the cytoplasm, which further indicates such QDs could be excellent candidate for two-photon microscopy applications.

The key factors on silicon-based tandem thin film solar cells

The key factor for high efficiency of tandem Si-based thin film solar cells is to optimize the whole configuration for improving its utilization of solar energy besides the active layers of device-quality level. Several aspects reached in our lab are discussed in this paper. A double structure of P+ window layer was proposed and studied. An interlayer between top-cell and bottom-cell in the tandem structure for forming a micro-cavity in top-cell was simulated by the software programmed by ourselves. Finally, the results of two types of tandem solar cells, namely, a-Si/a-Si and a-Si/μc-Si with the light trapping back-reflection structure are reported.

Controllable light utilization in silicon-based thin film solar cells

Controllable light utilization in silicon-based-thin-film solar cells with a DBR structure have been simulated. A experimental model cells constructed by a-Si pin/ZnO (~70 nm)/P+muc-Si(20 nm) were verified. The ratio of Isc increment can be reached to 14.1%.

Optical properties of core-multishell quantum dots and their imaging applications in cancer cells

Core-shell semiconductor quantum dot (QD) has been attracting more and more extensive attentions and interests in biomedicine photonics due to its good stability and high fluorescence quantum efficiency. In this paper, we reported that the photoluminescence of core-multishell CdSe QDs performed a two-photon action under a femtosecond laser excitation in wide incident power range. The two-photon absorption cross sections of such QDs were measured by the intensity-dependent transmittance method and the results demonstrated a very strong two-photon absorption capacity of QDs. The fluorescent spectra of QDs with an amphiphilic polymer showed that the fluorescent peak wavelength appeared blue shift obviously and the full width at half maximum (FWHM) broadened to 40 nm. Furthermore, the intracellular distribution of the QDs probes in cancer cells had been observed under two-photon excitation. The experimental results indicated that the QDs mainly distribute at cell membrane and selectively gathered on cytoplasm of cancer cells. The QDs which permeated into cancer cells quickly were very steady binding with cancer cells. Under long time laser irradiation, the QDs hardly took place photobleaching, which demonstrated a very steady photochemical performance of these QDs..