Optical properties of photochromic organic-inorganic composites

We prepared several photochromic composite films based on a hybrid organic- inorganic matrix in which metal heteropolyoxometallates are entrapped. Infr ared Fourier transform and W-Visible spectroscopic ellipsometry methods hav e been used for the first time to study the coloring/bleaching process of t he: composite films. Data on all samples were acquired using a J.A. Woollam Co. VASE instrument and WVASE software. The optical absorption of these sp in-coated films changed markedly by a reversible process, in the presence o r absence of UV irradiation. The VIS-NIR transmission data showed that the films containing tungsten heteropolyoxometallate (HPOM) had strong absorpti ons at about 720 nm, 1108 nm and the films containing molybdenum HPOM had a strong absorption at 720 nm. We have also extracted for the first time the visible and infrared optical functions of the films. For the colored films , the Lorentz and Gaussian oscillators were used to describe the optical be havior in the 400-1700 nm wavelength range and 700-4000 cm(-1) wavenumber r ange, respectively. The composite films containing tungsten heteropolyoxome tallate (HPOM) showed faster coloration and bleaching than pure tungsten ox ide films. The composite films with molybdenum HPOM showed faster coloratio n and much slower bleaching than tungsten HPOM. (C) 1999 Elsevier Science S .A. All rights reserved.