Effects of Rare Earth Impurities on Photochromic Characteristics of Rare Earth Orthoniobates

Abstract

Some rare earth orthoniobates, RNbO 4 , have been found to exhibit photochromic properties ascribed to the formation of color centers. Compounds with rare earths, R, of gadolinium and ytterbium, have been shown to have a particularly long duration of visible coloration after ultraviolet (UV) irradiation at room temperature. Partial substitution of praseodymium or terbium as the rare earths enhances these UV coloration characteristics. Substitution of about 0.8% of terbium is remarkably effective in accelerating the thermal bleaching, increasing the bleaching rate by about one order of magnitude.