Single phase CoFe2O4 thin films are deposited on quartz substrates at 400 °C using ultrasonic assisted chemical vapor deposition, and the tuning of optical bandgap and saturation magnetization of films is demonstrated by varying the post deposition annealing temperature. The optical band gap varies from 1.58 to 1.41 eV and saturation magnetization increases from 4 to 46 emu/g as the post deposition annealing temperature is increased from 500 °C to 700 °C. The observed change in optical bandgap and the magnetic properties is attributed of the shifting of Co2+ from the octahedral to the tetrahedral site with the increase in the annealing temperature. Raman studies of the films support the redistribution of Co2+ among the octahedral and tetrahedral sites in CoFe2O4 films with the increase in the annealing temperature.

NaNbO3/MoS2 and NaNbO3/BiVO4 core–shell heterostructures show absorption range extending to the visible region and high charge transfer rate at the interface and lower charge recombination which result in overall enhanced photocatalytic activity in the visible region. NaNbO3/MoS2 core–shell heterostructures show higher solar-to-hydrogen conversion efficiency due to better alignment between core and shell interface. The Rct and RIFCT values of NaNbO3/MoS2 core–shell (from EIS studies) are significantly smaller than in NaNbO3/BiVO4 core–shell heterostructures suggesting the charge separation in NaNbO3/MoS2 is more suitable and hence shows higher photocatalytic activity toward photoelectrochemical water splitting and dye degradation. The experimental results were well supported by photoluminescence as well as time-resolved spectroscopy. Enhancement of cathodic current in NaNbO3/MoS2 core–shell heterostructure and from Mott–Schottky plots also indicates appearance of the p–n junction formation between core and shell materials. The p–n junction assists in the separation of photogenerated charge carriers at the core–shell interface. Increasing the negative shift of the flat band potential for the NaNbO3/MoS2 photoelectrode suggested higher charge carrier concentration with reduced charge recombination in comparison with pristine MoS2, BiVO4, and NaNbO3/BiVO4 core–shell heterostructures. The enhanced performance makes these heterostructures ideal candidates for photoelectrochemical hydrogen evolution via water splitting.

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In this report, the tuning of the optical bandgap and saturation magnetization of cobalt ferrite (CFO) thin films through low doping of zinc (Zn) has been demonstrated. The Zn doped CFO thin films with doping concentrations (0 to 10%) have been synthesized by ultrasonic assisted chemical vapour deposition technique. The optical bandgap varies from 1.48 to 1.88 eV and saturation magnetization varies from 142 to 221 emu/cc with the increase in the doping concentration and this change in the optical and magnetic properties is attributed to the change in the relative population of the Co2+ at the tetrahedral and octahedral sites. Raman study confirms the decrease in the population of Co2+ at tetrahedral sites with controlled Zn doping in CFO thin films. A quantitative analysis has been presented to explain the observed variation in the optical bandgap and saturation magnetization.