We　report　for　the　first　time　the　synthesis　of　a　co-doping　oxide　system　by　introducing　Sc3+　to　co-doped　Al2O3　with　Yb　3+,　Er3+　and　Y3+　via　sol-gel　method.　The　green　and　red　upconversion　(UC)　luminescence　of　the　co-doped　Al2O　3　has　been　obviously　improved　with　the　increasing　of　the　amount　of　Sc3+.　Microstructures　of　the　co-doped　Al2O3　with　different　amounts　of　Sc3+　have　been　investigated　by　XRD,　HR-TEM,　NMR,　XPS　and　FT-IR　to　find　the　role　of　Sc3+　in　this　system,　and　several　key　changes　of　the　micro-nano-structure　have　been　revealed,　which　are　helpful　to　inhibit　the　factors　of　the　quenching　of　UC　luminescence.　With　the　increasing　of　Sc3+　co-doping　concentration,　the　Er3+　dispersity　has　been　improved,　the　distance　between　Er3+　and　OH　-　has　been　enlarged,　amount　of　OH-　absorption　has　been　reduced,　the　asymmetry　of　Er3+　local　surrounding　has　been　improved,　and　the　carbon　impurity　has　been　reduced.　As　the　results,　UC　luminescence　quenching　has　been　inhibited　greatly,　and　the　electronic　population　of　transition　levels　has　been　enhanced.　The　luminescence　intensity　can　be　enhanced　several　times　and　decay　time　can　be　extended　over　five　times.　This　research　may　be　useful　for　the　design　and　synthesis　of　high-performance　UC　co-doping　materials.　©　2013　Elsevier　Ltd.　All　rights　reserved.