In this paper, we investigate how various concentrations of potassium-doped MgO films affect the discharge characteristics in ac-type plasma display panel. The firing voltages of ion-doped MgO films indicate that the potassium ions in MgO film clearly produce a low discharge voltage. The static memory margin of a test panel decreases as the concentration of potassium ions increases. The X-ray photoelectron spectroscopy results, which confirm that the potassium doping creates donor energy levels in the band gap of MgO, agree well with the varied behavior of secondary electron emission yields in various K⁺-doped MgO films.