[en] Strong and high purity O^- negative ion emission has been observed from a synthesized crystal 12CaO·7Al₂O₃ surface. A μA/cm2-level O^- emission from this material has been achieved at the surface temperature of 800 deg. C and the extraction field over 1000 V/cm, which is about three orders of magnitude higher than the current density emitted from the Y₂O₃-stabilized ZrO₂ electrolyte surface. The strong emissivity of this material, as well as easy and economical fabrication, may provide a useful tool to generate the O^- negative ion, which is expected to be one of the most important radicals for chemical syntheses and material modifications