Activator ionization and deep level ionization in SrS:Ce ac thin-film electroluminescent devices

This report focuses on the ionization mechanism of dynamic space charge formation during ac thin-film electroluminescent device operation. Laser excitation under operating condition is used to identify the ionization mechanism. It is concluded, that Ce3+ ionization and ionization of other deep levels are forming the dynamic space charge. The charge emission process is impact excitation in combination with tunnel emission. The Ce3+ excited state is more than 0.23 eV below the conduction band and the ground state of other deep levels is more than 3.6 eV below the conduction band. (C) 1999 American Institute of Physics. [S0021-8979(99)07124-8].