A fluorescent chemical sensor platform, integrating an organic light-emitting device ͑OLED͒ light-source with a fluorescent probe, is demonstrated for a subsecond-fast oxygen sensor. The integration results in strong light coupling and negligible heating of the sensor film or analyte. The potential in vivo operation of compact, stand-alone, battery-powered, OLED-based miniaturized sensor arrays for chemical and biological applications is discussed.
Nanosecond electroluminescence ͑EL͒ overshoots observed when multilayer blue 4,4Ј-bis(2,2Ј -diphenyl vinyl)-1,1Ј-biphenyl ͑DPVBi͒-based organic light-emitting devices ͑OLEDs͒ are excited by rectangular voltage pulses are described. The overshoots occur at the voltage turn-off and exceed the cw brightness by up to an order of magnitude. Time-resolved images of the OLEDs demonstrate that the emission from most of the sample surface decays with a single time constant 1 ϭ13 Ϯ3 ns. This decay is attributed to recombination of charges which accumulate at the interface of the electron and hole transporting layers, possibly at intrinsic trapping sites. In areas of increased electron injection and EL, such as cathode edges and morphological defects, a second slower decay time 20 nsϽ 2 Ͻ1 s is observed, apparently due to release of carriers from localized trap states in the organic/cathode interface. Only marginal variations in 1 are found between bright and dim areas of the devices. At a bias of 10 V, the amplitude of the overshoot is found to peak at a pulse duration of ϳ20 s. Its behavior is believed to result from increased quenching of singlet excitons by the accumulated charges.
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