Dense and transparent cadmium tungstate (CWO) scintillation films have been first synthesized by sol-gel processing and their optical properties have been studied. Different precursors (tungsten oxychloride and tungstic acid), solvents (alcohol based and aqueous based) and thermal annealing processing conditions were investigated to achieve stable sols and resultant dense nanocrystalline CWO films. XRD showed CWO was the only detectable crystalline phase in the film derived by tungstic acid based sol and fast sintering at 500°C for 20 min, while the slow sintered films derived both from tungstic acid and tungsten oxychloride at 500°C for 1 hour with a heating ramp of 8°C/min resulted in porous films containing some extra tungsten oxide phases besides CWO. The fast sintered CWO film was uniform, fully dense, crack-free and of 0.5 μm in thickness. Optical transparency and photoluminescence of CWO films were characterized, and the results showed that high density and low porosity of CWO film by fast sintering led to higher transmittance and photoluminescence output. By controlling synthesis and sintering methods the nanocrystalline grains in CWO films can be of 15~52 nm in diameter. The relationships between sol-gel processing, precursor and solvent chemistry, nanostructures, densification and optical properties were discussed.
This paper reports experimental study on the development of cadmium tungstate scintillator material in the form of nanocrystal films through controlled sol-gel processing and pre-designed doping. We chose cadmium tungstate as a base material for doping and nanostructure development due to its excellent inherent photoluminescence property. In addition, our studies revealed that doping with Li+, B3+ and Bi3+ resulted in appreciably reduced grain size and porosity, leading to enhanced optical transmittance. Further analyses indicated that photoluminescence output changed significantly with dopants. The relationships between doping, defects and luminescence were discussed.
Optically transparent superhydrophobic silica-based coatings were obtained by means of sol-gel processing and self-assembling. Superhydrophobicity was achieved through a combination of enhanced surface roughness by incorporating nanoclusters and modification of surface chemistry by self-assembly. The self-assembly monolayer (SAM) was prepared using the chemical coupling reaction between chlorosilyl groups and hydroxylated coating surface. The optical transparence of such hydrophobic coatings was found to be higher than 95%, which is attributed to the fact that the roughness scale is too small to scatter the visible light. The water contact angle was of approximately 150°.