Ultraviolet absorbing photochromic glass of low silver content

摘要

There is disclosed a method of producing a photochromic glass having a reduced transmittance for ultraviolet radiation while having substantially unimpaired photochromic properties. The method comprises providing a combination of 0.1-1.0% CeO2 and 0.1-1.5% Sb2O3 and/or As2O3 as part of the glass composition. In an embodiment utilizing minimal silver content, the glass article in thicknesses of 1.3 to 2.0 mm. can be chemically strengthened to surpass the impact specification imposed by the Federal Food and Drug Administration for eyewear, will transmit less than 0.2% of radiation having wavelengths between 290-315 nm, and will demonstrate a darkened luminous transmittance at 20 DEG -25 DEG C. below 35% and a fading rate such that after five minutes the luminous transmittance will be at least 1.75 times that of the darkened transmittance. These glasses consist essentially of: -SiO2 55-61 Ag >0.1-<0.2 -B2O3 18-21 Cl 0.2-0.6 -Al2O3 5-11 Br 0.05-0.2 -Li2O 1.5-3 CuO 0.003-0.015 -Na2O 2-5 CeO2 0.1-1.0 -K2O 4.5-8 Sb2O3 0.1-1.5 -