An optical article including a core; at least one cladding layer; and a narrow fluorine reservoir between the core and the cladding layer. The fluorine reservoir has a higher concentration of fluorine than either the cladding layer or the core. One particular embodiment includes a core including a halide-doped silicate glass that comprises approximately the following in cation-plus-halide mole percent 0.25-5 mol % Al2O3, 0.05-1.5 mol % La2O3, 0.0005-0.75 mol % Er2O3, 0.5-6 mol % F, 0-1 mol % Cl.