Limin An

Room and Low temperature photoluminescence properties of CdSe quantum dots synthesized rapidly in aqueous approach

Thiol-capped CdSe quantum dots are synthesized rapidly in aqueous solution assisted by microwave irradiation without any poisonous materials. Room and low temperature photoluminescence is employed to investigate the excitonic emission from thiol-capped CdSe quantum dots between 83K and 293 K. The photoluminescence peak position of CdSe quantum dots shift to shorter wavelengths and the photoluminescence intensity first enhance and then quench with decrease of temperature. The temperature dependence of the PL spectra is demonstrated through thermal escape and thermal rectification of surface trap states.

The Metal-Enhanced Fluorescence of CdTe Quantum Dots under the Excitation of Femto Second Laser

This paper presents an investigation on the fluorescent properties of semiconductor CdTe quantum dots (QDs) self-assembled on the surface of PVP (polyvinylpyrrolidone) capped silver nanoparticles (NPs) film by ligand field effect under the two photons excitation of 800nm femto second laser. A significant enhancement by 4.5-fold in the integrated fluorescence intensities, red shift of fluorescence peak and obvious decrease of lifetime were observed in the CdTe QDs assembled on the Ag NPs film in comparison with the pure CdTe QDs on the glass. The fluorescence enhanced factor is larger on the solid film than in the liquid. The fluorescence enhancement factor and red shift were found to depend on the Ag NPs concentration. The fluorescence enhancement was contributed to high localized electromagnetic field generated by the surface plasma on the Ag NPs and the change of surface trap state of CdTe QDs originating from plasma oscillations in the Ag NPs.

Temperature Effect of Photoluminescence from Aqueous CdSe Quantum Dots

Thiol-capped CdSe quantum dots are synthesized rapidly in aqueous solution assisted by microwave irradiation without any poisonous materials. The growth rate of quantum dots is greatly enhanced in this current microwave synthesis. The narrow size distribution (~30nm) of CdSe quantum dots is similar to the oil samples. The results indicate that the photoluminescence quality of quantum dots is improved effectively assisted by microwave irradiation compared to traditional aqueous solution. Room and low temperature photoluminescence is employed to investigate the excitonic emission from thiol-capped CdSe quantum dots between 83K and 300K. The photoluminescence peak position of CdSe quantum dots shift to shorter wavelengths. The relationship between the shift wavelengths and the temperature is linear. The slope for linear fitting curve is nearly constant in repeated experiment. This implies CdSe quantum dots may be applied in the low temperature nano-sensor. The photoluminescence intensity first enhances and then quench with decrease of temperature. The temperature dependence of the photoluminescence intensity is demonstrated through thermal escape and thermal rectification of surface trap states.

Figures Method for Mast Valuating Interpolation Errors of Encoder with High Precision

Figures method is based on the lissajou graph of more fringe photoelectric signal. The waveform generator produce signal of simulation, the signal lissajou graphs and actual collection of signal lissajou graphs fitting to and comparison. Through the goodness-of-fit parameters of judgement, we can determine parameters of actual waveform. Then we can get the photoelectric signal to meet the equation. The final can draw the subdivision error curve. The figures method can be used in the working field, avert the influence of the speed, and has important meaning to the improvement of high precision encoders dynamic precision characteristics.

The simulation and analysis on the radiation fence of D-D neutron generator by Monte Carlo Method

This paper simulates and analyses the irradiation fence around D-D neutron generator by a method, which combines Monte Carlo and practical measurement. Setting up the model of MCNP(the analog Monte Carlo method for Neutron and Protons transport) and analyzing the results are introduced. The energy of neutron from neutron generator is 2.5 MeV. Water has been used as the material of neutron fence. We use the MCNP procedure to simulate them and find the relation between the thickness of the fence material and the quantity of neutron injection. We take the result as a basis for designing the rapied analyzer of cement raw meal using D-D neutron generator. The results approve that Monte Carlo can be used in radiation protection analysis and optimum design of radiation source shield.

An appraisal method of dynamic interpolation error for high precision encoder

This paper introduces an appraisal method of the dynamic interpolation error for the high precision encoder (Lissajou pattern calculation method). When the encoder is rolling, two groups of fine photoelectric signals whose phase difference are π/2 can be collected using data collected car. The shape and position deviation can be obtained through the comparison between Lissajou charts and the standard circle. Then dynamic interpolation error can be calculated out directly. This method is immune to the influence of encoders speed and has no rigid demand to the test circumstances and test devices. The experimental results indicate that this method is feasible and important to the encoders dynamic interpolation error checking.

Aqueous synthesis and photoluminescence properties of CdSe/CdS core/shell quantum dots

Thiol-capped CdSe/CdS core/shell quantum dots which show high luminescence quantum yield are synthesized in aqueous solution with the application of ultrasonic irradiation. A combination of X-ray diffraction (XRD), UV-Vis absorption spectroscopy and photoluminescence spectroscopy are employed to analyze the QDs and determine their crystal structures and optical characters. Photostabilities of bare CdSe and CdSe/CdS core/shell QDs are compared under UV irradiation.

Figures deduction method for mast valuating interpolation errors of encoder with high precision

With the development of technology, especially the need of fast accurately running after and orientating the aim of horizon and air, the photoelectrical rotary encoder with high precision has become the research hotspot in the fields of international spaceflight and avigation, the errors evaluation of encoder with high precision is the one of the key technology that must to be resolved. For the encoder with high precision, the interpolation errors is the main factor which affects its precision. Existing interpolation errors detection adopts accurate apparatus such as little angle measurement apparatus and optics polyhedron, requesting under the strict laboratory condition to carry on. The detection method is also time-consuming, hard to tackle and easy to introduce detect errors. This paper mainly studies the fast evaluation method of interpolation errors of encoder with high precision which is applied to the working field. Taking the Lissajous figure produced by moiré fringe as foundation, the paper sets up the radius vectors mathematical model to represent figures form deviation, analyses the implied parameters information of moiré fringe, the relation of the radius vector deviation and interpolation errors in the figures and puts forward the method of interpolation errors figures evaluation. Adopting figure deduction method, and directly from harmonic component of radius vector deviation toward harmonic component of interpolation errors, the interpolation errors can be gotten in the paper. Through data collecting card, the Moiré fringe signal is transmitted into the computer, then, the computer storages the data, using figures evaluation method to analyses the data, drawing the curve of interpolation errors. Comparing with interpolation errors drawing from traditional detect method, the change trend of the interpolation errors curve is similar, peak-peak value is almost equality. The result of experiment indicates: the method of the paper can be applied to evaluate interpolation errors of high precision encoder, which need simple equipment and the examination method is efficient and feasible; Apart from these, the data processing can be realized by valuation analysis software, and the time is short, the result manifestation is intuitionistic; the system can be used in the working field, avert the influence of the speed, and has important meaning to the research of high precision encoders dynamic precision characteristics.

The theoretical basis of the moiré fringe signal quality detecting by observing the figures

The moiré fringe signal quality decides the precision of the encoder. In the production process of RESR, usually, the moiré fringe signal quality is detected by the Lissajou graphs observing by the oscilloscope. Lissajou graph is the common method for analyzing the dc level of two analog signals, the amplitude of alternating current, the phase of signal, the relation of frequencies and other parameters. It is convenient, intuitive, and would not be affected by the rate; furthermore, it applies to be used for field detection. The ideal moiré fringe signal has two sine signals which phase difference is 90°, and prefect round Lissajou graph. However, in practice, for a variety of factors, moiré fringe photoelectric signal has dc level, higher harmonic, orthogonality deviation, equal amplitude deviation, and so on; that is why Lissajou graph will appear offset or distortion. So we can observe the shapes deviation of the Lissajou graph in order to judge the signal deviations. This paper introduces the diameter deviation to describe deviation between the Lissajou graph of actual signal and the Lissajou graph of ideal signal, establishes the mathematical model of diameter deviation, and theoretically analyzes the relationship between the diameter deviation and the parameters of moiré fringe photoelectric signal. Using the VB6.0 simulation software to prove the results of the theoretical analysis, we find that the simulation results agree with the previous detection, which supply theoretical foundation for the observation of Lissajou graph. After analyzing the character of the encoders signal when the encoder works in a uniformly accelerated motion, we point out the applicative conditions of the observation of Lissajou graph detecting moiré fringe signal. The conclusions of this paper have important significance for detecting the signal quality of encoder, and have certain reference value for detecting other signals.