In this paper, we investigate the decomposition of a toxic organic compound, Rhodamine B, by the photocatalytic activities of undoped and nitrogen-doped ZrO₂ thin films, deposited using the HiPIMS technique. The investigation was performed in the presence and in the absence of H₂O₂, for two types of experimental arrangements: the irradiation of the films, followed by dipping them in the Rhodamine B solutions, and the irradiation of the films dipped in the solution. The two situations were named “direct irradiation” and “indirect irradiation”, respectively. Methods like XRD, AFM, XPS, DRS, water/film surface contact angle, and spectrophotometry were used to obtain information on the films’ structure, surface morphology, elemental composition of the films surface, optical band gap, hydrophilicity, and photocatalytic activity, respectively. All these properties were described and correlated. By N-doping ZrO₂, the films become absorbent in the visible domain, so that the solar light could be efficiently used; the films’ hydrophilic properties improve, which is an important fact in self-cleaning applications; and the films’ photocatalytic activity for the decomposition of Rhodamine B becomes better. The addition of hydrogen peroxide acted as an inhibitor for all systems and not as an accelerator of the photocatalytic reactions as expected.

Amorphous ZrO₂ thin films with increasing Mg content were deposited on quartz substrates, by dip coating method. The films are transparent in the visible domain and absorbent in UV, with an optical band gap that decreases with the increase of Mg content, from 5.42 eV to 4.12 eV. The temperature dependent conductivity measurements showed typical semiconductor comportment. The decrease of the electrical conductivity by Mg doping was related to the increase of the OH groups (37% to 63%) as seen from X-ray Photoelectron Spectroscopy. It was found out that the electrical conductivity obeys the Meyer-Neldel rule. This rule, previously reported for different disordered material systems is obtained for ZrO₂ for the first time in the literature. Exploring novel aspects of Mg-doped ZrO₂, the present study underscores the origin of the Meyer-Neldel rule explained by the small-polaron hopping model in the non-adiabatic hopping regime. Determination of the presence of such a conduction mechanism in the samples hold promise for comprehending the important aspects, which might be a concern in developing various devices based on Mg-doped ZrO₂.

In this paper, we have investigated the photocatalytic performances of some yttrium-doped ZrO₂ films for decomposing Rhodamine B and Methylene Blue. The as-deposited thin films (obtained by RF magnetron sputtering) were heat-treated to stabilize their structure. To assess the films’ characteristics, a group of analytical methods (XRD, XPS, AFM and DRS) allowed for the determination of their structural, surface, and optical properties. These characteristics were correlated with the observed photocatalytic activity and wetting behaviour. The Y-doped ZrO₂ film with medium nanoparticle size and a high contribution of the oxygen vacancy is found to be more efficient in Rhodamine B and Methylene Blue photodegradation; the 100% degradation efficiency was reached in 70 min and 40 min, respectively, for the 3 mg/L solution dye. The photodegradation mechanism is driven by photogenerated holes, and a possible reaction mechanism was proposed. By investigating the charge carrier separation at the film–ITO interfaces, made through a comparative analysis of their determined band edge potentials, we conclude that the transfer is not possible in either of the semiconductor pairs, so ITO does not “help” the photocatalytic process.