Bulk Zn1−xCoxO samples were synthesized via standard solid-state reaction route with different Co molar concentrations up to 21%. A detailed microstructural analysis was carried out to investigate alternative sources of ferromagnetism, such as secondary phases and nanocrystals embedded in the bulk material. Conjugating different techniques we confirmed the Zn replacement by Co ions in the wurtzite ZnO structure, which retains, however, a high crystalline quality. No segregated secondary phases neither Co-rich nanocrystals were detected. Superconducting quantum interference device magnetometry demonstrates a paramagnetic Curie–Weiss behavior with antiferromagnetic interactions. We discuss the observed room temperature paramagnetism of our samples considering the current models for the magnetic properties of diluted magnetic semiconductors.

The main goal of this work is to provide a general description of the negative photoconductivity effect observed in Ag/AgO films grown by the spray-pyrolysis technique. X-ray diffractograms display hybrid films with high texturized AgO and metallic Ag phases. Scanning electron microscopy images show small Ag particles on the surface. Due to its surface nature, X-ray photoelectron spectroscopy revealed the predominance of the metallic character of Ag 3d spectra as compared to Ag²⁺. Negative photoconductivity with photoresponse in the order of seconds is observed under several wavelengths of excitation. We found that the amplitude of the negative photoresponse is strongly dependent on the optical absorbance and enhanced by surface plasmon resonance. The low-cost technique employed and the special features regarding negative photoconductivity provide an exciting platform for developing optical-electronic devices with low power consumption.