SOL-GEL GLASSES - A NEW MATERIAL FOR SOLAR FLUORESCENT PLANAR CONCENTRATORS

Inorganic glasses prepared by the "cold" chemical sol-gel process can present an alternative host material for organic fluorescent dyes. We report on measurements done on thin SiO2 layers prepared as sol-gels and doped with various dyes on a glass substrate. The preparation is done by dip-coating of the substrate in the corresponding alcoxide solutions. Good-quality layers without crazing after drying are achieved with a thickness of up to 1-2 mu-m. The measurements include absorption measurements (UV to IR), fluorescence and excitation measurements (visible to NIR), and measurements of photo-decomposition. The optical properties of the dye molecules in the layer and in the sol-gel solutions are studied as a function of dye concentration and changes in the thermal treatment of the layers. The results are examined for their applicability to fluorescent planar concentrators. Further we report on small silver islands (submicron size) brought into the sol-gel solution as stabilised colloids or by chemical reduction of Ag+ salts. According to theoretical predictions, the electromagnetic interaction between silver surface plasmons and dye molecules can result, under certain conditions, in an enhanced fluorescence quantum efficiency and photostability of the dye.