New black color insulator thin films comprising Pr oxide, composite oxides of Pr-Mn, Pr-Ni, Pr-Co or Mn oxide are used to constitute at least one part or all parts of interface film between a phosphor film and a back electrode film of an AC thin film EL panel; and the panel with such a high contrast as 5:1 even at an illumination of 400 lux has been obtained.
