Organometallic blue
fluorescent Zn(II) Schiff base complexes are
synthesized and explored computationally in order to use them in organic
electroluminescent heterostructures. Characterization of these pyrazolone-based
azomethine–zinc complexes was accomplished by various physicochemical
techniques to get insight into their applicability as an active layer
in light-emitting diodes. All the complexes demonstrate high thermal
stability and remarkable photoluminescence both in solution and in
the solid state with maximum in the blue region. Quantum chemical
calculations of the first exited electronic state and vertical singlet–singlet
electronic transitions by means of time-dependent density functional
theory calculations and results show that the origin of the luminescence
for the target complexes refers to the intraligand charge transfer
within the Schiff bases. The constructed light-emitting diodes demonstrate
low input voltage (3.2–4.0 V), brightness at a level of 4300–11,600
Cd m–2, and external quantum efficiency of up to
3.2%, which is a good value for purely fluorescent organic light-emitting
diodes.
CdTe/CdS core-shell quantum dots were synthesized and implemented into a light emitting device resulting in multi-channel electroluminescence with a light-green emission colour. The main electroluminescence band at about 530 nm corresponds to the emission by the CdTe core (type I core/shell structure), while the next emission band at 595 nm is assigned to the crossed recombination of electrons from the conduction band of the CdS shell and holes from the valence band of the CdTe core (type II core/shell structure). At the same time, the photoluminescence spectrum of the synthesized CdTe/CdS core-shell quantum dots contains only one emission band distinctive for type II structures. This behavior of CdTe/CdS core-shell quantum dots upon the electroexcitation allows the extension of the electroluminescence spectrum in the optical region in a way that is useful for the lighting-source applications. Such multi-channel electroluminescence can most probably also be reproduced in related core-shell systems accounting for size-confinement between the core size and shell thickness.
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