The color change of aluminosilicate gel-derived glasses doped with CoO

Aluminosilicate gel-derived glasses of 0.5CoO . 5Al(2)O(3). 94.5SiO(2) comp osition were obtained by the sol-gel method. The samples were transparent, and their color depended on heat-treatment temperature. The gel sample pres ented a pink color but, when heat-treated at temperatures higher than 43 de grees C, acquired amethyst and purple colors. The samples heat-treated at 1 20 and 250 degrees C showed an evident modification of color from amethyst to pink when in contact with air humidity. The changes from pink to amethys t and purple were related to the ability of Co(II) to act as a network form er and/or modifier. Ultraviolet (UV), visible (VIS) and near-infrared (NIR) spectrophotometry, X-ray diffraction (XRD), and scanning electron microsco py (SEM) were the techniques used to obtain information about the relations hip between the glass structure and the color of the samples, (C) 2000 Else vier Science Ltd.