High efficiency and low operating voltage yellow phosphorescent organic light-emitting diodes with a simple doping-free structure.

Yellow phosphorescent organic light-emitting diodes (PhOLEDs) with high efficiency and a low operating voltage were reported through using a simple doping-free structure. The structure of the PhOLEDs was ITO/C60/MoO3/mCP/PO-01-TB/PO-T2T/Liq/Al. The np-type C60/MoO3 heterojunction acted as hole injection layer, and the ultrathin PO-01-TB layer (0.1 nm) was inserted at the interface between mCP and PO-T2T to serve as yellow phosphorescent emitter. Detailed investigation suggested that the complete energy transfer occurred from the mCP/PO-T2T interfacial exciplex to yellow PO-01-TB. Furthermore, the np-type C60/MoO3 heterojunction could supply more free charge carriers, giving rise to further enhanced PhOLED efficiency. By adjusting the thickness of the C60/MoO3 heterojunction, a yellow PhOLED with a power efficiency of 71.6 lm W-1 was demonstrated with an extremely low operating voltage of 3.79 V at 1000 cd m-2.

Tuning the microstructural and magnetic properties of CoFe2O4/SiO2 nanocomposites by Cu2+ doping.

Co-Cu ferrite is a promising functional material in many practical applications, and its physical properties can be tailored by changing its composition. In this work, Co1-x Cu x Fe2O4 (0 ≤ x ≤ 0.3) nanoparticles (NPs) embedded in a SiO2 matrix were prepared by a sol-gel method. The effect of a small Cu2+ doping content on their microstructure and magnetic properties was studied using XRD, TEM, Mössbauer spectroscopy, and VSM. It was found that single cubic Co1-x Cu x Fe2O4 ferrite was formed in amorphous SiO2 matrix. The average crystallite size of Co1-x Cu x Fe2O4 increased from 18 to 36 nm as Cu2+ doping content x increased from 0 to 0.3. Mössbauer spectroscopy indicated that the occupancy of Cu2+ ions at the octahedral B sites led to a slight deformation of octahedral symmetry, and Cu2+doping resulted in cation migration between octahedral A and tetrahedral B sites. With Cu2+ content increasing, the saturation magnetization (M s) first increased, then tended to decrease, while the coercivity (H c) decreased continuously, which was associated with the cation migration. The results suggest that the Cu2+ doping content in Co1-x Cu x Fe2O4 NPs plays an important role in its magnetic properties.