Deep blue light-emitting diodes based on Cd1−xZnxS@ZnS quantum dots

We demonstrate deep blue light-emitting diodes based on chemically synthesized Cd(1-x)Zn(x) S @ ZnS quantum dots (QDs). Composite films of poly-(N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine) (poly-TPD) and 4,4',N,N'-diphenylcarbazole (CBP) are employed for facilitated hole injection into Cd(1-x)Zn(x) S @ ZnS QDs and uniform QD deposition. The fabricated devices possess moderate turn-on voltage (6 V) and external quantum efficiency (0.1-0.3%), and exhibit color-saturated blue emission with a narrow spectral bandwidth of full width at half maximum <25 nm (Commission Internationale de l'Eclairage (CIE) coordinates of (0.169, 0.024) and (0.156, 0.028) for devices with electroluminescence (EL) lambda(max) at 434 and 454 nm, respectively). Most of the emission originates from the Cd(1-x)Zn(x) S @ ZnS QD layers (99% of the total EL emission).