Ultraviolett absorbierende Gläser

A non-photochromic R2O-B2O3-SiO2 glass containing a cuprous or cuprous-cadmium halide crystal phase, having a sharp spectral cutoff at about 400 nm, the glass composition consisting essentially of, in cation percent, 35-73% SiO2, 15-45% B2O3, 0-12% Al2O3, the Al2O3 being less than 10% when the SiO2 is over 55%, 0-12% Li2O, 0-20% Na2O, 0-12% K2O, the Li2O+Na2O+K2O being 4.75-20%, 0-5% CaO+BaO+SrO, 0.125-1.0% Cu2O, 0-1% CdO, 0-5% ZrO2, 0-0.75% SnO2, 0-1% As2O3 and/or Sb2O3, the glass containing 0-1.75% Cl, 0-1.0% Br, 0.25-2.0% Cl+Br and 0-2% F by weight, and having an R-value, calculated in mole percent of 0.15-0.45, the R-value not exceeding 0.30, except as the glass composition meets at least one condition selected from the group: up to 12 cation % Li2O, less than 10 cation % Al2O3, at least 0.3 cation % Cu2O and 0.50-2.0% Cl+Br. Also, a method of making the non-photochromic glass having a sharp spectral cutoff.