Electroluminescence from doped ZnS nanocrystals polymer composite systems

ZnS, ZnS:Cu and ZnS/CdS nanocrystals were synthesized in polymer matrices with a variety of methods. TEM, absorption spectra and small-angle X-ray scattering studies showed that the particle sizes of ZnS, ZnS:Cu and ZnS/CdS nanocrystals were 3.0, 3.2 and 2.0nm respectively. Electron diffraction results showed that the ZnS and CdS nanocrystals have the hexagonal structures and Cu ions existed in ZnS with the form of Cu2S. A hole transport material tetraphenylbenzidine(TPB) were also doped into ZnS nanocrystals/polymer to improve the electroluminescent(EL) property of the ZnS nanocrystals. ZnS:Cu, ZnS/CdS and TPB/ZnS nanoparticles/polymer composite as emitters were used to fabricate a single layer structure light-emitting diode between ITO and Al electrodes respectively The photoluminescent and EL properties of these doped systems were studied. These EL devices had low turn on voltage(less than or equal to 4V) and the blue electroluminesence from Cu:ZnS and ZnS/CdS and a violet-blue electroluminescence from TPB:ZnS were observed respectively at room temperature under ambient air. The EL mechanism is also discussed.