Photo-and Electro-Luminescence in Copper Doped Zinc Sulphide Nanoparticles and Nanocomposites

Abstract

Copper doped Zinc Sulfide (ZnS:Cu)) is a known green light emitter. Present paper reports luminescence of ZnS:Cu nanoparticles and nanocomposites. Three different nanostructures: mercaptoethanol capped ZnS:Cu nanoparticles, polyvinyl alcohol (PVA) capped ZnS:Cu nanoparticles and ZnS:Cu/PVA nanocomposites have been prepared by chemical route. X-ray diffraction (XRD) revealed cubic zinc blende structure of ZnS:Cu nanocrystals of size below 20 nm. The particle size is found to decrease with increasing capping agent concentration or ZnS loading in PVA matrix. Optical absorption spectra show blue shift in the absorption edge indicating quantum size effect. Photoluminescence (PL) of all the samples was studied by exciting with 212 nm light. The PL spectra of ZnS:Cu/ PVA nanocomposite films show quite broad emission peak at 415 nm where as the PL spectra of mercaptoethanol capped and PVA capped nanoparticles show a very narrow peak at 426 nm and 403 nm respectively. It seems that the nature of passivation of surface states affects the position of surface states. Electroluminescence (EL) studies have shown that light emission starts at a threshold and then increases with voltage. Higher EL intensity and lower threshold voltage is obtained in case of smaller particles. The EL spectra of all the samples are found to be broad with peak at about 420 nm. The EL intensity of ZnS:Cu/PVA nanocomposites is much larger than the ZnS:Cu nanoparticles. The high efficiency EL devices for display and lighting can be fabricated using ZnS:Cu nanocomposites with PVA matrix giving violet emission.