Sol-gel deposition and luminescent properties of oxyapatite Ca-2(Y,Gd)(8)(SiO4)(6)O-2 phosphor films doped with rare earth and lead ions

Rare-earth and lead ions (Eu3+, Tb3+, Dy3+, Pb2+) doped Ca2Y8 (SiO4)(6)O-2 and Ca2Gd8(SiO4)(6)O-2 thin films have been dip- coated on silicon and quartz glass substrates through the sol- gel route. X- Ray diffraction (XRD), TG- DTA, scanning electron microscopy (SEM), atomic force microscopy (AFM), FT- IR and luminescence excitation and emission spectra as well as luminescence decays were used to characterize the resulting films. The results of XRD reveal that these films remain amorphous below 700 degreesC, begin to crystallize at 800 degreesC and crystallize completely around 1000 degreesC with an oxyapatite structure. The grain structure of the film can be seen clearly from SEM and AFM micrographs, where particles with various shapes and average size of 250 nm can be resolved. Eu3+ and Tb3+ show their characteristic red (D-5(0)-F-7(2)) and green (D-5(4) - F-7(5)) emission in the films with a quenching concentration of 10 and 6 mol% (of Y3+), respectively. The lifetime and emission intensity of Eu3+ increase with the temperature treatment from 700 to 1100 degreesC, while those of Tb3+ show a maximum at 800 degreesC. Energy transfer phenomena have been observed by activating the oxyapatite film host- lattice Ca2Gd8(SiO4)(6)O-2 with Tb3+ (Dy3+). In addition, Pb2+ can sensitize the Gd3+ sublattice in Ca2Gd8(SiO4)(6)O-2.

Optical properties of organo-soluble polyimide thin films and their applications in liquid crystal displays

Three organo-soluble polyimide powders have been synthesized. Their imidization was verified by Fourier transform infrared (FTIR) and thermal gravimetric analysis (TGA) techniques. The amorphous morphology of their thin films were confirmed by X-ray diffraction. Polyimide thin films were prepared by solution casting or spin coating. UV-visible transmission spectra of thin films revealed that they are almost transparent in the range of visible light. With in-plane orientation, revealed by FTIR spectra, negative birefringence (Delta n) of thin films were observed, and refractive indices of the thin films along the film plane (n(TE)) and normal to the plane (n(TM)) were measured by a prism coupler. Because of negative birefringence of the thin films, they tan be substituted for the compensation films for twisted nematic liquid crystal displays (TN-LCDs) to extend their viewing angles. In this paper, a 90 degrees C TN-LCD and 120 degrees C TN-LCD were taken as examples to show the compensation effect of thin films of a qualified polyimide. (C) 1998 Elsevier Science S.A. All rights reserved.

Microstructure and wear properties of laser clad Fe based amorphous composite coatings

A FeNiSiBV amorphous composite coating was developed by laser cladding of metallic powders on AISI 1020 low carbon steel substrate. The coatings were studied using X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The coating reveals different microstructures along the depth of the coating. The transition zone exhibits good metallurgical bonding between the substrate and the coating. The layer consists of amorphous phase in majority and nanocrystalline phase/crystalline phase in minority. Accompanied with the nanocrystalline phase, the amorphous phase is concentrated in the middle of the coating. The crystalline phase in the coating is identified as Fe2B. A gradient distribution of the microhardness ranges from 1208 HV0.2 to 891 HV0.2 in the coating along the depth. The coating shows higher microhardness and better wear property than the substrate.