FIELD QUENCHING EFFECTS IN POLYCRYSTALLINE SRS-PB ACID SRS-CE,PB THIN-FILMS FOR ELECTROLUMINESCENCE DEVICES

The luminescence properties of lead ions and their sensitizing effect on cerium activators in strontium sulfide thin-film electroluminescenc e (TFEL) devices have been investigated. Polycrystalline SrS:Pb and Sr S:Ce,Pb thin active layers for such TFEL devices have been prepared by multi-source deposition. Emission spectroscopy under application of a high electric field (EL), under e-beam excitation [cathodoluminescenc e (CL)], and under CL conditions with additional EL drive has been car ried out. It has been found that the luminescence of SrS:Pb under EL d rive is very weak, while the CL signal is considerably higher. This CL signal has shown strong quenching effects upon application of an addi tional ac voltage. The Pb2+ emission dropped to some 5% at an applied voltage of 100 V-0p, being roughly 40 V below EL threshold. More than half of this drop occurred between 0 and 30 V-0p. A remarkably lower q uenching effect on the Ce3+ activator luminescence has been observed. Such luminescence quenching is attributed to the field induced ionizat ion of the luminescent ions. From the obtained results it is concluded that the optical energy transfer from Pb2+ sensitizers to Ce2+ activa tors in SrS TFEL devices is low. (C) 1996 American Institute of Physic s.