ABSTRACT
Defect engineering is a promising method for improving light harvesting in photocatalytic materials like Zinc sulphide (ZnS). By altering the S/Zn molar ratio during hydrothermal processes, Zn and S defects are successfully introduced into the ZnS crystal. The band structures can be modified by adding defects to the crystal structure of ZnS samples. During the treatment process, defects are formed on the surface. XRD and Raman studies are used for the confirmation of the crystallinity and phase formation of the samples. Using an X-ray peak pattern assessment based on the Debye Scherer model, the Williamson-Hall model, and the size strain plot, it was possible to study the influence of crystal defect on the structural characteristics of ZnS nanoparticles. The band gap (Eg) values were estimated using UV-Vis diffuse spectroscopy (UV-Vis DRS) and found that the Eg is reduced from 3.28 to 3.49 eV by altering the S/Zn molar ratio. Photoluminescence study (PL) shows these ZnS nanoparticles emit violet and blue radiations. In keeping with the results of XRD, TEM demonstrated the nanoscale of the prepared samples and exhibited a small agglomeration of homogenous nanoparticles. Scanning electron microscopy (SEM) was used to examine the surface morphology of the ZnS particles. Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and X-ray photoelectron spectroscopy (XPS) were used to evaluate and validate the elemental composition. XPS results indicate the presence of defects on the prepared ZnS nanoparticles. For the investigation of vacancy-dependent catalytic activity under exposure to visible light, defective ZnS with different quantities of Zn and S voids are used as catalysts. The lowest S/Zn sample, ZnS0.67 and the highest S/Zn sample, ZnS3, show superior photocatalytic activity.
ABSTRACT
Praseodymium (Pr)-doped ZnS nanoparticles were synthesized using a low-cost microwave-assisted technique and investigations on their structure, morphology, optical properties, Raman resonance, dielectric properties, and luminescence were conducted. Broad X-ray diffraction peaks suggested the formation of low-dimensional Pr-doped ZnS nanoparticles with a cubic structure that was validated using transmission electron microscopy (TEM)/high-resolution TEM analysis. The energy gaps were identified using diffuse reflectance spectroscopy and it was found that the values varied between 3.54eV and 3.61eV for different samples. Vibrational experiments on Pr-doped ZnS nanoparticles revealed significant Raman modes at ~270 and ~350 cm-1 that were associated with optical phonon modes that are shifted to lower wavenumbers, indicating phonon confinement in the synthesized products. The photoluminescence (PL) spectra of all samples demonstrated that the pure and Pr-doped ZnS nanoparticles were three-level laser active materials. Energy-dispersive X-ray spectroscopy and mapping study confirmed the homogeneous presence of Pr in ZnS. TEM studies showed that the particles were of very small size and in the cubic phase. The samples had high dielectric constant values between 13 and 24 and low loss values, according to the dielectric analysis. With an increase in frequency and a change in the Pr content of ZnS, an intense peak could be seen in the PL spectra at a wavelength of 360 nm, and some other peaks observed corresponded to the transition of Pr3+ . The produced nanoparticles were appropriate for optoelectronic applications due to their short dimension, high energy gap, high dielectric constant, and low loss values.
