Isotopic ¹⁰BN sheets were first prepared using graphene sheets as templates to react with ¹⁰B₂O₃. The edge-areas of BN sheets have much higher oxygen-doping ratios compared to other areas. The emission peak of X-ray excited optical luminescence spectra of the ¹⁰BN-sheets is broader and red-shifted because of the isotopic effect. A broad violet–blue emission at a wavelength centered at ∼400 nm is assigned to the defect emission due to oxygen-doping and defects in the BN network.