Pulsed magnetic resonance of Alq3 OLED detected by electroluminescence

The aim of the present work is to investigate the nature of spin dependent processes in an organic light emitting diode based on a ITO/alpha-NPD/Alq(3) structure. The electroluminescence time response of the sample is monitored while the OLED is exposed to a high power resonant microwave pulse. Measurements are carried out at room temperature. The time scale of the induced transition is found to be independent of the bias voltage. It is shown, by way of a simulation, that this behavior appears inconsistent with models which attribute a change in the electroluminescence to a variation in charge mobility. Spin dependent processes directly related to a change in the rate of charge recombination play therefore a relevant role in Alq(3) light emitting diodes. (c) 2013 Elsevier B.V. All rights reserved.