GLASS COMPOSITION AND OPTICAL ELEMENT

PROBLEM TO BE SOLVED: To provide a high-refractive and low-dispersive glass composition having a refractive index (nd)≥1.70 and an Abbes's number (νd)=35-55, having a glass transition temperature (Tg) low enough to exhibit an excellent ability to be press-molded, and having excellent moldability. SOLUTION: The glass composition contains 10-35 wt.% B2O3, 10-40 wt.% La2O3, 10-60 wt.% ZnO+ZnF2(0-45 wt.% ZnO), and 0.5-9 wt.% Li2O+LiF, provided that the total content of fluorine compounds is 9-15 wt.%. To attain a still lower Tg, it is desirable that the composition further contains at least either 0-5 wt.% K2O or 0-5 wt.% Na2O. To attain an improvement an mechanical strengths, the adjustment of optical constants, and an improvement in chemical tolerance, the composition may further contain one or more components selected from among 0-20 wt.% SiO2, 0-20 wt.% Y2O3, 0-15 wt.% Nb2O5, 0-20 wt.% Bi2O3, 0-5 wt.% ZrO2, 0-15 wt.% BaO+BaF2, 0-10 wt.% CaO+CaF2, 0-15 wt.% Ta2O5, 0-15 wt.% WO3, 0-10 wt.% TiO2, and 0-10 wt.% Al2O3. COPYRIGHT: (C)2003,JPO