Factors affecting the UV-Transparency of Molecular Sieves

The optical properties in the UV-region of several types of molecular sieves were studied. The initial onset of absorption around 280 nm which was observed for basically all samles synthesized without special precautions is not due to an early onset of band gap absorption, but might be correlated to the crystal size as well as structural defects within the crystals, e.g. E'-center or peroxy-radical. Using template free synthesis procedures which lead to small crystals containing few defect sites, we were able to synthesize molevular sieves which were almost completely transparent down to 200 nm. Such crystals can become very important in the development of technical luminophores.