A numerical study of the problem of diffraction at a locally deformed plane wave-guide

We present a rigorous solution for the problem of diffraction at a locally deformed plane wave-guide. This method can be applied to the study of mode coupling and mode conversion.     

Preparation of organic-inorganic nano-composites for antireflection coatings

In this research, bi-layer thin film stacks that served as an antireflective coating were developed. The top layer was synthesized using tetraethoxysilane and 3-(trimethoxysilyl) propyl methacrylate by the well-known sol-gel technique. Its refractive index was lower than that of the bottom layer, which was prepared by reaction between tetrabutoxyltitanium and γ-glycidoxy propyl trimethoxysilane. Antireflective coatings were obtained by spin-coating of the synthesized sols on a glass substrate, followed by pre-drying, UV-curing, and post-baking. Fourier transform infrared spectrometer was employed to investigate the evolution of chemical bonds during the UV-curing and the sol-gel processes. The size of the inorganic/organic hybrid particles in the sol was found to be less than 10 nm, as measured by transmission electron microscope and dynamic light scattering. Thermo gravimetric analyzer was used to find out the thermal degradation temperature of the two layers and the effect of post-baking. The results indicated that the thermal stability increased after post-baking at 200 °C for 15 min. The reflectance of the antireflection coating was controlled by the relative refractive indices and the thickness of the top and bottom layers. Under optimal synthesis condition, we obtained an antireflection coating, exhibiting a low reflection, 1% at 550 nm, in the visible range.     

Effects of structure and composition of the CaP composite coatings on apatite formation and bioactivity in simulated body fluid

The surface properties of biomaterials determine the interactions between biomedical devices and the surrounding biological environment. The surface modification of biomaterials is extensively recognized as a key strategy in the design of the next generation of bone implants and tissue engineering. In this study, the highly ordered octacalcium phosphate (OCP) coating and OCP/protein coating with hierarchically porous structure in nano-micro scale were constructed on titanium substrate by electrochemically-induced deposition (ED). The formation behavior of apatite on OCP and OCP/protein coatings immersed in simulated body fluid (SBF) was investigated in physicochemical aspects. It is indicated that soaked in SBF, the OCP and OCP/protein coatings are possible to induce relevant apatite formation on their surface, and the apatite-forming behavior in body environment is depended on the chemical composition and structure of the coatings. The apatite formed on OCP/protein composite coating possesses carbonated structure, needle-like crystals in nano scale, lower Ca/P ratio and higher degree of the preferred c-axis orientation, which are similar to the mineral composition and structure in natural bone, and hence called as bone-like apatite.     

Amplification properties of Tb (III) green emission in polymeric waveguide doped with Tb-Al nanocluster

This paper describes optical amplification properties in a polymeric waveguide doped with Tb-Al nanoclusters. The Tb-Al nanocluster is a promising fluorescent material for polymeric waveguides, which can be uniformly dispersed in polymer matrices while restraining the concentration quenching of Tb³⁺. Under the continuous optical pumping by 488 nm laser light, optical amplification for the green emission of Tb³⁺ was achieved. The optical gain coefficients were estimated to be as high as 0.25 and 0.56 mm⁻¹ at the Tb-Al nanocluster concentrations of 4.5 and 5.0 wt%, respectively. Taking into account our previous works for the polymeric waveguide doped with Eu-Al nanocluster, the rare-earth-metal nanocluster is believed to be a promising candidate for various photonic applications such as multicolor polymer lasers and waveguide-type optical amplifiers.     

Material characterization of a nanocrystal based photovoltaic device

Nanocomposites have shown promise as the active layer for photovoltaic energy conversion. One example is the CdSe nanocrystal \polymer composite demonstrated by Hyunh and Greenham [#!Ref1!#,#!Ref2!#]. In this paper we investigate the baseline properties of the materials used in such a device. We present surface chemical information for CdSe nanocrystals and chemical analysis for poly-(3-hexylthiophene) (P3HT) polymer. Received 30 November 2000     

Photon cascade emission of Pr~(3+) in LnBaB_9O_(16) (Ln = La, Y)

Under 216 nm UV-excitation, cascade emission of Pr3+ occurs from 1S0 state in LaBaB9O16:Pr3+ that converts a single UV photon of high energy into two visible photons. The observation of the cascade emission in this oxide matrix is largely due to the weak crystal field on the lanthanum sites. The analysis of the vibrational coupling indicates that the radiative transition from the 3P0 state is related to the low phonon frequency of the BO4 borate groups bonded to the lanthanum atoms (hwmax-850cm-1). On the other hand, the cascade emission does not take place in a closely related material, YBaB9O16:Pr3+, which can be interpreted by the fact that the 4f5d levels are located below the 1S0 level in this material.     

GdP5O14:Sm3+,Pr3+晶体生长,光谱和离子间的能量传递

离子间能量传递;光催化剂;GdP5O14:Sm3+;Pr3+晶体生长;光谱和离子间的能量传递     

NUMERICAL SIMULATION OF BENARD CONVECTION IN A CLOSED RECTANGLE (Ⅰ)——TWO-DIMENSIONAL CASE

In the paper, a finite differential numerical model is proposed for Benard convection ina non-slippery closed rectangle. By this model, we have discussed the bifurcation character-istics of two-dimensional Benard convection when Prandtl number is 1. The computed re-sults show that if the Rayleigh number Ra≥1.75×10~5, the Benard convection is unsteady andirregular, and that in the transient region of flow pattern, the changing rate of the Nusseltnumber Nu to Ra, dlgNu/dlgRa, is rather smaller than that in the non-transient region.Moreover, in the paper, we have analysed the relation between the shrinking rate of thephase flow and each term in the governing equations of Benard convection. And further,we have developed a new method to calculate the pressure gradient.     

新型蓝绿色稀土荧光粉SrZnO2:pr3+的发光性能

运用柠檬酸溶胶-凝胶法合成了SrZnO2:Pr3 和SrZnO2:Pr3 ,M (M=Li,Na,K)系列新型蓝绿色稀土荧光粉。用X射线粉末衍射(XRD)、荧光光谱(PL)、拉曼光谱(Raman)等手段研究了样品的物相结构和光致发光性能。SrZnO2:Pr3 荧光体的激发光谱是一个主峰位于262nm处的宽带谱。其发射主峰位于490nm附近,样品在紫外光照射下发出蓝绿色荧光。SrZnO2:Pr3 荧光体的猝灭浓度为0.1mol%。在该荧光体中共掺碱金属离子Li ,Na ,K ,能增大样品的激发和发射强度。