Luminescence study of ZnS/PVK nanocomposites

Abstract

Sulphide-based luminescence materials have attracted more curiosity for their extensive applications in electro and photoluminescence devices. One of the sulphides, such as zinc sulphide (ZnS), is a favourable material for phosphor growth in various bands for visible emission. The composition of the polymer matrix with ZnS demonstrates its special functions and stabilizes the nanoparticles. We have used chemical methods for the preparation of ZnS/PVK nanocomposites and reported their synthesis, photoluminescence (PL), and electroluminescence (EL) studies. The samples were analyzed through SEM (Scanning Electron Microscope), AFM (Atomic Force Microscope), and XRD (X-ray Diffraction). The XRD study shows the formation of ZnS nanocrystals with a cubic crystal structure, having a size between 3 and 12 nm and the broadening of peaks shows the formation of an amorphous compound. The AFM and SEM show clusters of particles in the range of a few tens to a few hundred nm. The results from all three studies show an increase in the size of particles with the ZnS loading in PVK (poly N-vinylcarbazole). The PL of a PVK sample excited at 400 nm shows a single PL peak at 451 nm and covers the spectral range from 400 to 600 nm. ZnS/PVK samples excited by 370 nm, give a PL peak due to PVK near 450 nm and when excited by 425 nm, the PL peak is found near 470 nm due to defect-related transitions in ZnS. In both cases, PL intensity increases with increasing ZnS loading in PVK. This may be because of interfacial charge transfer and radiative recombination. The EL studies show that corresponding to the applied voltage, the brightness is increased. The EL emission starts at a lower threshold voltage with a higher loading of ZnS in PVK and at a higher threshold voltage for higher frequencies. EL intensity of the composites increases with increasing ZnS loading in PVK. The voltage-current curve shows the linear relationship between voltage and current that is ohmic in nature. The frequency of applied voltage increases as impedance decreases.