Size Dependent Electroluminescence from CdSe Nanocrystallites (Quantum Dots)
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ABSTRACT We obtain spectrally narrow (FWHM < 40 nm) electroluminescence from nearly monodisperse CdSe nanocrystallites (quantum dots) incorporated into thin films of polyvinylcarbazole (PVK) and an oxadiazole derivative (PBD) sandwiched between aluminum and ITO electrodes. The electroluminescence and photoluminescence spectra are nearly identical at room temperature and are tunable from -530 nm to ~650 nm by varying the size of the dots. Voltage studies at 77K indicate that while only the dots electroluminesce at the lower voltages, both the dots and the PVK matrix electroluminesce at higher applied voltages. Variable temperature studies indicate that the electroluminescence efficiency increases substantially as the films are cooled down to cryogenic temperatures.
INTRODUCTION Semiconductor crystallites which are smaller than the corresponding bulk exciton diameter exhibit strong quantum size effects and are often referred to as quantum dots.' Their absorption spectrum has discrete features which move to higher energy with decreasing dot diameter and a "band edge" luminescence spectrum tunable with dot size. Quantum dot/conducting polymer structures allow for direct electrical connection and excitation of the dots. In this paper we describe electroluminescence from a solid state assembly of nearly monodisperse (Y
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