Influence of heat treatment on the transparency of silicate thin films in the near-IR range

The influence of heat treatment on the transmission of silicate thin films prepared by gelation from aqueous solutions of sodium silicate (water glass) is investigated. It is demonstrated that the initial films are characterized by a strong absorption in the IR range due to the presence of hydroxyl groups. The heat treatment of the films at temperatures in the range 150-250°C leads to the step-by-step removal of water from the films and, as a consequence, to an almost complete transmission in the high-frequency IR spectral range. An increase in the heat treatment temperature to 580°C is accompanied by the loss of transparency, most likely, as a result of the pore formation in the film. © 2008 MAIK Nauka.