Highly Luminescent Colloidal CdS Quantum Dots with Efficient Near Infrared Electroluminescence in Light-Emitting Diodes

Quantum dots are of growing interest as emissive materials in lighteinitting devices. Here first we report the formation of highly luminescent organic capped colloidal cadmium sulfide (CdS) hanoparticles having the highest photoluminescence quantiim yield of 69% in solutions and 34% in neat thin films in the near -infrared range. Second, we also show efficient electroluminescence in the near,infrared from solution processed hybrid light emitting diodes (LEDs) based on such, colloidal CdS quantum dots embedded in an organic semiconductor matrix forming a nanocomposite active layer. We also discuss the device structure and role of the doped:active- layer in efficiency improvement. With optimized active layer thickness and concentration of QDs, the device exhibits an external electroluininescence quantum efficiency of 0.62% at a peak emission wavelength of 760 nm, providing a route to solution processablerflexible light sources for biosensors and medicine.