Group　IV　semiconductor　optoelectronic　devices　are　now　possible　by　using　strain-free　direct　band　gap　GeSn　alloys　grown　on　a　Ge/Si　virtual　substrate　with　Sn　contents　above　9%.　Here,　we　demonstrate　the　growth　of　Ge/GeSn　core/shell　nanowire　arrays　with　Sn　incorporation　up　to　13%　and　without　the　formation　of　Sn　clusters.　The　nanowire　geometry　promotes　strain　relaxation　in　the　Ge0.87Sn0.13　shell　and　limits　the　formation　of　structural　defects.　This　results　in　room-temperature　photoluminescence　centered　at　0.465　eV　and　enhanced　absorption　above　98%.　Therefore,　direct　band　gap　GeSn　grown　in　a　nanowire　geometry　holds　promise　as　a　low-cost　and　high-efficiency　material　for　photodetectors　operating　in　the　short-wave　infrared　and　thermal　imaging　devices.