Role of PVA capping on photophysical properties of chemically prepared CdS nanomaterials: Insights on energy transfer mechanisms in the capped system

摘要

Radiative and nonradiative relaxation mechanisms of carriers in CdS nanomaterials capped by polyvinyl alcohol (PVA) and energy transfer processes between PVA and intrinsic vacancies or defects in CdS have been investigated in the present work. Highly luminescent PVA encapsulated CdS nanomaterials have been synthesized via chemical co-precipitation method with varying PVA concentration. XRD shows a hexagonal (wurtzite) structure of nanomaterials with crystallite sizes ranging from 6 nm to 10 nm. Surface morphology shows spherical shapes of agglomerated nanoclusters; additive makes them more compact and further agglomerated within the nanomaterials. Blue shifting in absorption band of as-synthesized nanomaterial from that of bulk reveals the effect of quantum confinement. Urbach energy is increased; accordingly, the band gap of nanomaterials is also decreased with addition of PVA in CdS. Photoluminescence emission spectroscopy indicates that both excitonic and defect emission intensities are enhanced due to the suppression of nonradiative recombination. The role of interaction between PVA and CdS in controlling emission colours and intensity has been explored. Chromaticity analysis reveals tunability in emission colours with high colour purity. Luminescence quantum efficiency and electroluminescence efficiency have also been assessed. Observed enhancement in optical properties makes the capped CdS nanomaterials promising for future generation QD LED applications.