Figure 4

UV–Vis (a) absorption spectra of CuO, ZnO, and CuO@ZnO core/shell NPs, (b) transmittance spectra of CuO, ZnO, and CuO@ZnO core/shell NPs (c) variation of ln (αhν) with ln (hν–E_g) to determine the type of transition, and (d) Direct allowed optical bandgap.