The incorporation of Bi in GaSb1-xBix alloys grown by molecular beam epitaxy is investigated as a function of Bi flux at fixed growth temperature (275 degrees'C) and growth rate (1 mu m h(-1)). The Bi content is found to vary proportionally with Bi flux with Bi contents, as measured by Rutherford backscattering, in the range 0 < x <= 4.5%. The GaSbBi samples grown at the lowest Bi fluxes have smooth surfaces free of metallic droplets. The higher Bi flux samples have surface Bi droplets. The room temperature band gap of the GaSbBi epitaxial layers determined from optical absorption decreases linearly with increasing Bi content with a reduction of similar to 32 meV/'%'Bi. (C) 2015 The Authors. Published by Elsevier B.V.