Organic-inorganic Complex Electroluminescence And White Emission Via Organic Heterojunction

1.High-quality ZnS:Mn²⁺/ZnS core/shell nanocrystals(NCS) with core crystal diameter of 6.1 nm and 1.15 nm thick shell were synthesized via high-boiling solvent process and used as the active material in electroluminescence(EL) devices.The conduction band and valance band energy levels were measured to be -3.2 eV and -6.8 eV by cyclic voltmmetry(CV) data and UV-Vis absorption spectra..A weak emission peak at 460 nm and a strong emission peak at 580 nm are observed in room temperature photoluminescence spectrum of ZnS:Mn²⁺/ZnS core/shell NCs.EL devices using ZnS:Mn²⁺/ZnS core/shell NCs as emission layer were fabricated: ITO//PEDOT:PSS//ZnS:Mn²⁺/ZnS core/shell NCs//LiF(0.5 nm)//Al(device a); ITO//PEDOT:PSS//PVK//ZnS:Mn²⁺/ZnS core/shell NCs//LiF(0.5 nm)//Al(device b). EL emission was observed at a low direct current(dc) bias voltage.Compared to device without PVK layer,the hybrid PVK-based device showed large current flow and considerably enhanced EL emission.These observations are shown to be consistent with the energy level diagrams of the EL device.2.Influences of electric fields on the emission from organic light-emitting diodes (OLEDs) based on poly(N-vinylcarbazole)(PVK),2,9-dimethyl-4,7-diphenyl-1, 10-phenanthroline(BCP) and tris(8-hydroxyquinoline) aluminum(Alq₃) are studied. There are three emission peaks at 420nm,520nm and 620nm of device ITO/PEDOT: PSS/PVK/BCP/LiF/Al under different driving voltages.The emissions at 420nm and 520nm should be from the exciton emission of PVK and Alq₃,respectively.After the study of PL and absorption spectrum of double layer PVK/BCP thin film,exciplex emission could be excluded.The new emission should be attributed to electroplex emission at the interface of PVK and BCP.It was spatially cross electron transfer from LUMO of BCP to HUMO of PVK.A high intensity white emission via electroplex formation was obtained with Commission International d'Eclairage(CIE) coordinates (0.33,0.34) at 15V,which is very close to the equienergy white point(0.33,0.33).We also noticed that the CIE coordinates is voltage-insensitive from 15 to 23V.When the applied voltage varied,the CIE coordinates only shows a slight shift from(0.33,0.34) to(0.32,0.36).