Defects induced photoluminescence and alteration of band gap and morphology in Ca doped sol-gel co-precipitated ZnO nanoparticles
Mahesh Malpani, Khushabu Shekhawat, Saikat Chattopadhyay, R.D.K. Misra, Kamakhya Prakash Misra
Abstract
This study investigates the structural, morphological, and optical properties of undoped ZnO and Ca-doped ZnO nanoparticles synthesized via co-precipitation method with varying Ca concentration (1, 2, 5, and 10 at%). X-ray diffraction (XRD) studies proposed hexagonal wurtzite structure with the lattice parameters: a = 3.2447 Å, c = 5.2 Å belonging to the space group P63mc, in all the samples, alongside the emergence of CaCO₃ secondary phases at specific angles (29.50°, 39.42°, and 43.24). In regard optical and structural characteristics, band gap modulation (3.15, 2.95, 3.04, 3.10 and 2.95 eV) was exhibited by ultraviolet (UV) transmission observations as Ca amount increases, which showed a small redshift in the absorption edge (371–375 nm) with increased Ca concentration. The introduction of defect states and Ca-related trap centres led to increased visible emission intensity (370, 405, 430 and 465 nm) with doping as revealed in photoluminescence (PL) studies. Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed characteristic vibrational modes of ZnO, with minor shifts in the spectra of Ca-doped samples, implying influence of Ca doping on the vibrational properties of ZnO lattice. A significant change in morphology from clustered flakes to irregular shapes with increasing Ca content was observed by scanning electron microscope. Energy-dispersive X-ray spectroscopy (EDX) studies confirmed successful incorporation of Ca in the ZnO lattice (0.5–7.0 at%). The study provides valuable insights into the effect of Ca doping on structural and morphological properties of ZnO, which are envisaged to be crucial for optimizing its performance in varied applications such as optoelectronics, sensors, and catalysis.