Silicoborate and borosilicate glasses having high refractive index and low density

A glass, comprising:

• SiO2 from 0.3 wt % to 30.0 wt %;
• B2O3 from 0.3 wt % to 30.0 wt %;
• Nb2O5 from 11.23 wt % to 50.0 wt %;
• CaO from 0.5 wt % to 25.0 wt %;
• at least one oxide selected from ZrO2, SrO, Li2O, MgO, ZnO, Y2O3, Ta2O5, BaO, PbO, TiO2, Gd2O3, GeO2, K2O, La2O3, and Na2O, subject to the proviso that:
• ZrO2 from 2.5 wt % to 15.0 wt %, if present;
• Gd2O3 from 0.0 wt % to 20.0 wt %;
• Y2O3 from 0.0 wt % to 10.0 wt %;
• TiO2 from 0.0 wt % to 6.77 wt %;
• ZnO from 0.0 wt % to 2.0 wt %;
• Li2O from 0.0 wt % to 2.0 wt %;
• GeO2 from 0.0 wt % to 2.0 wt %;
• Ta2O5 from 0.0 wt % to 1.0 wt %;
• and
• wherein the glass is further defined by (in percent by weight of oxides):
• a sum of (Nb2O5+TiO2) of from 18.0 wt % to 50.0 wt %;
• a sum of (SiO2+B2O3) of from 1.0 wt % to 30.0 wt %;
• a sum (La2O3+Gd2O3) of from 0.0 wt % to 40.0 wt %;
• a sum (CaO+SrO+BaO) of 8.1 wt % or greater;
• a sum (PbO+V2O5) of from 0.0 wt % to 1.0 wt %;
• a ratio CaO/(Li2O+Na2O+K2O+MgO+CaO+SrO+BaO+ZnO) of 0.50 or greater;
• a ratio (SiO2/(SiO2+B2O3)) of greater than 0.0 to less than or equal to 0.50;
• and
• a ratio (CaO+SrO+BaO)/(Nb2O5+TiO2) of 0.45 or greater, and
• wherein the glass is substantially free of fluorine;
• and
• wherein none of the ranges is modified by the term “about”.