Hi

electron-hole recombination from the bottom of the conduction band and nearby localized states to wide-range valance band is suggested as origin of the fluorescence.You can check the link for more details.

http://www.nature.com/srep/2012/121031/srep00792/full/srep00792.html

There is chance for some contribution from the Mn2+ ions also , which can be there with the GO as byproduct of the synthesis procedure.

Great question!! The answer is yet not clear exactly. However wide range pi pi stacking

cluster and bond distortion might be responsible for fluorescence. Thanks 

Formation of little PAH islands can be reason for the fluorescence

hi dear/ read this article..

DOI: 10.1038/srep00792