On characteristics of PVA/CdS and PVA/CdS:Cu nanocomposites for applications as LED

We report the synthesis of poly vinyl alcohol/cadmium sulphide (PVA/CdS) and polyvinyl alcohol/cadmium sulphide:copper (PVA/CdS:Cu) nanocomposites by chemical route. Characterizations are done by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), ultra violet–visible (UV–VIS), photoluminescence (PL), energy dispersive X-ray spectroscopy (EDS) and selected area electron diffraction (SAED). Sizes of the fabricated nanoparticles (NCs) obtained from XRD are in good agreement with those from TEM/HRTEM and confinement is found to be strong in some samples. The photoluminescence (PL) spectra show luminescence from band edge emission (481 nm) as well as from trap levels caused by sulpher vacancies (510 nm, 538 nm, 572 nm) and from defect states in case of doped sample (500 nm). The photoluminescence and electroluminescence (EL) spectra without as well as with applied (DC) bias are also studied using platinum electrodes in liquid samples. Results indicate that peak position remains same in both the cases of PL and EL and intensity is roughly an increasing function of excitation voltage. Encouraged by the results obtained so far, which indicates possible applications of the samples fabricated as LED, nano devices with ITO/N,N′-bis(3 methylphenyl)–N,N′-bis(phenyl)benzidine (TPD)/NC/Al have been fabricated to study the EL spectra. Operating voltages for PVA/CdS light emitting device (LED) is 0.2 V and for PVA/CdS:Cu light emitting device (LED) is 0.1 V. The emission dominantly belongs to CdS nanocrystals (NCs). Highest external quantum efficiency estimated for the PVA/CdS nanocomposites LED is 0.0024%. The highest external quantum efficiency gets increased upto 0.0027% after doping the PVA/CdS nanocomposites with Cu.