Gap-state induced photoluminescence quenching of phenylene vinylene oligomer and its recovery by oxidation

We demonstrate that the gap states at the interface of Ca and a phenylene vinylene oligomer thin film are responsible for the dramatic quenching of its photoluminescence (PL). Upon oxidation of the Ca layer, the midgap states are removed, and the PL intensity recovers. From the cumulative Ca deposition and oxidation study, a 30 Angstrom Ca oxide layer between the oligomer and the Ca metal prevents PL quenching due to metal induced midgap states. The implications of these results in the design and operation of organic light-emitting devices are discussed.