Electronics property luminance efficiency

The luminescent centers require a range of properties that include a large cross-section for the collision excitation to occur, an ionic radius and valency to fit the lattice and be stable under the applied high electronic fields, and the capability to display high luminous efficiency when excited.11 Metal ions suitable for EL devices include Mn, Tb, Sm3+, Tm3+, Pr3+, Eu2+, and Ce3+.12-17 ZnS lattices doped with Mn2+ (yellow-orange emission at ca. 585 nm) have proved to be one of the best phosphors for EL devices. 

The primary effect of the anode modification on the enhancement in luminous efficiency and the increased stability of OLEDs can be attributed to an improved hole-electron current balance. By choosing an interlayer with a suitable thickness of a few nanometers, anode modification enables engineering of the interface electronic properties. The above results indicate that conventional dual-layer OLEDs of ITO/NPB/Alq3/cathode have an inherent weakness of instability that can be improved by the insertion of an ultrathin interlayer between ITO and HTL. The improvements are attributed to an improved ITO-HTL interfacial quality and a more balanced hole electron current that enhances the OLED performance. 

It is evident from the above discussion that the threshold voltage, current density, power efficiency, luminous efficiency and, to some extent, device lifetime of OLEDs using organic low-molar-mass compounds, oligomers and polymers depends on intrinsic molecular properties, such as HOMO and LUMO energy levels, efficiency of hole and electron injection and subsequent transport, efficiency of singlet formation and fluorescence efficiency. The... 

This proposal was in line with the improved luminance efficiency identified as the result of an enhanced balance in the charge carrier transport properties. In this case, it was proposed that the electrons would spread into the semiconductor, thereby causing the halide to be detached from the polymer backbone on contact formation between the cathode material and the PPV. The anions produced in this way would drift either in the self-induced electric field established by the cathode close to the electron reservoir, or in the external electric field. The subsequent precipitation that would be expected to occur would result in a chemical modification of the interface region of the contact materials that, ultimately, would cause aging and fatigue of the device. 

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