Structural, optical and EPR studies on ZnO:Cu nanopowders prepared via low temperature solution combustion synthesis

Highlights: → ZnO:Cu nano particles are prepared via solution combustion technique with ODH fuel at low temperature. → Analysis of X-ray line broadening and micro strain in nanoparticles are evaluated using W-H plots. → PXRD results confirm that the nanopowders exhibit hexagonal wurtzite structure. → Decrease in the green emission and enhancement of UV emission in Cu doped ZnO due to the decrease in defects. → EPR spectrum exhibits a broad resonance signal at g ∼ 2.049 and two narrow resonances one at g ∼ 1.990 and other at g ∼ 1.950. - Abstract: Cu (0.1 mol%) doped ZnO nanopowders have been successfully synthesized by a wet chemical method at a relatively low temperature (300 deg. C). Powder X-ray diffraction (PXRD) analysis, scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Fourier transformed infrared (FTIR) spectroscopy, UV-Visible spectroscopy, Photoluminescence (PL) and Electron Paramagnetic Resonance (EPR) measurements were used for characterization. PXRD results confirm that the nanopowders exhibit hexagonal wurtzite structure of ZnO without any secondary phase. The particle size of as-formed product has been calculated by Williamson-Hall (W-H) plots and Scherrer's formula is found to be in the range of ∼40 nm. TEM image confirms the nano size crystalline nature of Cu doped ZnO. SEM micrographs of undoped and Cu doped ZnO show highly porous with large voids. UV-Vis spectrum showed a red shift in the absorption edge in Cu doped ZnO. PL spectra show prominent peaks corresponding to near band edge UV emission and defect related green emission in the visible region at room temperature and their possible mechanisms have been discussed. The EPR spectrum exhibits a broad resonance signal at g ∼ 2.049, and two narrow resonances one at g ∼ 1.990 and other at g ∼ 1.950. The broad resonance signal at g ∼ 2.049 is a characteristic of Cu2+ ion whereas the signal at g ∼ 1.990 and g ∼ 1.950 can be attributed to ionized oxygen vacancies and shallow donors respectively. The spin concentration (N) and paramagnetic susceptibility (χ) have been evaluated and discussed.