Gallium　nitride　quantum　dots　(GaN　QDs),　as　a　third-generation　semiconductor　material,　are　usually　synthesized　through　a　vapor　deposition　method　at　an　elevated　temperature　(typically　＞=　800　degrees　C).　Thermal　injection　method　is　rarely　reported　for　the　synthesis　of　GaN　QDs　due　to　the　lack　of　active　precursors　and　the　require　of　harsh　reaction　conditions.　Here,　we　report　the　fabrication　of　oxygen　doped　colloidal　GaN　QDs　via　rapid　thermal　injection.　By　screening　the　reaction　temperature　and　solvent,　well-dispersed　GaN　QDs　with　a　size　of　3.8　nm　were　obtained　in　octadecylamine　(ODA)　at　360　degrees　C.　The　synthesized　GaN　QDs　show　blue　emission,　the　maximum　emission　wavelength　is　about　440　nm,　and　the　photoluminescence　quantum　yield　is　14.3%.　Furthermore,　we　reveal　the　donor-acceptor　mechanism　of　blue　emission　from　GaN　QDs.　During　the　growth　of　GaN　QDs,　oxygen　atoms　occupy　some　nitrogen　sites　and　produce　a　shallow　oxygen　donor　energy　level　(ON).　A　part　of　the　ON　can　be　combined　with　the　adjacent　gallium　vacancy　(VGa)　to　form　a　VGa-ON　acceptor,　whose　energy　level　is　about　0.98　eV　above　the　valence　band　of　GaN　QDs.　The　transition　of　excited　electrons　from　the　donor　(ON)　to　the　acceptor　(VGa-ON)　is　responsible　for　the　blue　emission　of　GaN　QDs.