Abstract: High rare-earth content glasses (Ln.sub.2 O.sub.3 .gtoreq.20 mol %) have applications as high optical density wavelength-selective filters, faraday rotators, scintillation glasses and high index glasses. New glasses are formed by adding TiO.sub.2 to the system SiO.sub.2 --B.sub.2 O.sub.3 --Al.sub.2 O.sub.3 --Ln.sub.2 O.sub.3. These glasses have improved optical properties, extended glass formation range and have superior resistance to devitrification. In some embodiments TiO.sub.2 can fully replace the Al.sub.2 O.sub.3. In additional embodiments, SiO.sub.2 can be completely removed from the glass.