A simple, effective and ligand-free route toward cadmium sulfide nanocrystals on titanium plate: Insights into their crystal structure, local structure and optical properties

Abstract

Considerable attention on semiconducting nanocrystallines have been paid owing to their fascinating electrical and optical features, which can be utilized as luminophor and light absorber. Herein, we report a facile and ligand-free protocol to synthesize high-quality CdS nanocrystals on titanium plate. The crystal structural, micro-structural, local structural, surface chemistry and optical properties of CdS nanocrystals have been investigated. pH value dependent optical features of CdS nanocrystals are explored by photoluminescence and UV–vis diffuse reflectance spectroscopy. XRD results manifest that these products possess polycrystalline characteristics, cubic zinc-blende structure and nanomaterial features. The crystal defects and microstructure of these nanocrystals are researched by analysis of XRD line profiles. TEM images display nearly spherical nanocrystals with mean size about 4 nm, well crystalline feature and interplanar spacings of cubic zinc-blende CdS nanocrystals. Raman results also reveal the cubic sphalerite structure of CdS nanocrystals. The first three Raman peaks are assigned to the first, second, and third-order longitudinal optical phonon modes of cubic CdS, respectively. Interestingly, optical absorption spectra display that the absorbance shoulder shows a noticeable change with pH value of the precursor. The observations show that the nanocrystalline size is smaller at lower pH value and it changes as the pH value of the precursor alters, and CdS nanocrystals exhibit significant quantum confinement. More importantly, Photoluminescence spectra show that the first emission peaks can be attributed to band-edge luminescence, which is originated from the recombination of shallow trapped hole-electron pairs and/or excitons in cadmium sulfide nanomaterials, while the second emission peaks can be corresponded to trap-state luminescence, and PL intensity changes with the pH value of the precursor. The insights offered in this work may pave the way to devising of improved synthetic schemes for semiconductor nanocrystals with tailored microstructural properties, permitting precise adjusting of the optoelectronic performances of the prepared materials.