Effect of annealing temperature on structural, optical and electrical properties of CdO nanoparticles for lighting applications

Cadmium oxide (CdO) nanoparticles (NP) were prepared using mechanical milling and annealing. The CdO powders were grinded for 16 h using Agate mortar and Pestle and subjected to air annealing at 400 °C, 500 °C, 600 °C and 700 °C for one hour. The powder samples annealed at different temperatures were subjected to various characterization techniques such as XRD, UV–Vis-NIR spectroscopy, FT-IR spectroscopy, Raman spectroscopy, photoluminescence spectrophotometer and electrical measurements. The XRD results confirmed the polycrystalline cubic structure of the CdO nanoparticles. Rietveld analysis from XRD revealed the structural formation of CdO nanoparticles. The crystallite size decreased from 33 to 24 nm with an increase in annealing temperature. The chemical bonds in FT-IR spectra confirmed the formation of CdO nanoparticles. Raman spectra of the CdO nanparticles were recorded at room temperature and observed two distinct peaks at 269 cm−1 and 956 cm−1. Optical absorbance and reflectance spectra were recorded using UV–Vis-NIR spectrophotometer and the optical band gap of the nanoparticles were calculated using Tauc’s relation and Cody’ method. A decrease in the band gap was observed in both methods. The PL spectra of the CdO nanoparticles were recorded at room temperature with an excitation wavelength of 380 nm and observed emission peaks at 423 nm, 485 nm, 532 nm, and 606 nm. The electrical resistivity of the CdO nanoparticles was studied using two-probe method using the Keithley source meter and observed decrease in resistivity with annealing temperature. Graphical abstract