ZnO, Al-doped ZnO (AZO), and Ga-doped ZnO (GZO) semiconductor thin films were deposited on glass substrates via a sol-gel spin-coating process for application in a photoconductive ultraviolet (UV) detector. The doping concentrations of Al and Ga were 1.0 at % in the precursor solutions. In this study, the microstructural features and the optical and electrical properties of sol-gel-derived ZnO, AZO, and GZO thin films were compared, and the performance of ZnO-based UV photodetectors under ultraviolet A (UVA) light were measured. Experimental results confirmed the synthesis of single-phase nanocrystalline ZnO-based thin films and the successful substitution of Al and Ga into Zn sites in ZnO crystals. The results also demonstrated that the optical transmittance and electrical properties of ZnO thin films could be improved by Al and Ga doping. UV photodetectors based on ZnO-based thin films, having a metal-semiconductor-metal (MSM) configuration, were fabricated with Al inter-digitated electrodes. All photodetectors showed an ohmic nature between semiconductor and electrode contacts and exhibited a sharp increase in photocurrent under illumination with UVA light. We found that the MSM UV photodetector based on the GZO semiconductor thin film exhibited the best UV response (I_UVA/I_dark) of 73.3 and the highest photocurrent responsivity of 46.2 A/W under UVA light (power density ~0.825 mW/cm²) at 5 V bias.

A polyaniline (PANI)/tin oxide (SnO₂) composite for a CO sensor was fabricated using a composite film composed of SnO₂ nanoparticles and PANI deposition in the present study. Tin oxide nanoparticles were synthesized by the sol-gel method. The SnO₂ nanoparticles provided a high surface area to significantly enhance the response to the change in CO concentration at low operating temperature (<75 °C). The excellent sensor response was mainly attributed to the relatively good properties of PANI in the redox reaction during sensing, which produced a great resistance difference between the air and CO gas at low operating temperature. Therefore, the combination of n-type SnO₂ nanoparticles with a high surface area and a thick film of conductive PANI is an effective strategy to design a high-performance CO gas sensor.

The effects of Mg on the microstructural, optical, and electrical properties of sol-gel derived ZnO transparent semiconductor thin films and the photoelectrical properties of photodetectors based on Mg_xZn_1−xO (where x = 0 to 0.3) thin films with the metal-semiconductor-metal (MSM) configuration were investigated in this study. All the as-synthesized ZnO-based thin films had a single-phase wurtzite structure and showed high average transmittance of 91% in the visible wavelength region. The optical bandgap of Mg_xZn_1−xO thin films increased from 3.25 to 3.56 eV and the electrical resistivity of the films rose from 6.1 × 10² to 1.4 × 10⁴ Ω·cm with an increase in Mg content from x = 0 to x = 0.3. Compared with those of the pure ZnO thin film, the PL emission peaks of the MgZnO thin films showed an apparent blue-shift feature in the UV and visible regions. The photo-detection capability was investigated under visible, UVA, and UVC light illumination. Linear I-V characteristics were obtained in these ZnO-based photodetectors under dark and light illumination conditions, indicating an ohmic contact between the Au electrodes and ZnO-based thin films. It was found that the pure ZnO photodetector exhibited the best photoconductivity gain, percentage of sensitivity, and responsivity under UVA illumination. Under UVC illumination, the photoconductivity gain and percentage of sensitivity of the MgZnO photodetectors were better than those of the pure ZnO photodetector.

Three kinds of magnesium-based spinel nanoferrites with the chemical formulas of MgFe₂O₄ (Mg ferrite), Mg_0.9Mn_0.1Fe₂O₄ (Mg-Mn ferrite), and Mg_0.9Mn_0.1In_0.1Fe_1.9O₄ (Mg-Mn-In ferrite) were synthesized by hydrothermal route. We report the composition-dependent magnetic parameters and microwave properties of Mg-based ferrite nanoparticles. XRD results revealed that the Mg-based ferrite nanoparticles exhibited a cubic spinel structure and had an average nanocrystallite size in the range of 5.8–2.6 nm. Raman spectroscopy analysis confirmed the formation of cubic-spinel phase Mg-based nanoferrites. The room-temperature magnetization measurements indicated that the Mg ferrite nanoparticles had superparamagnetic behavior; whereas the Mg-Mn and Mg-Mn-In ferrite nanoparticles exhibited a paramagnetic nature. The microwave properties of obtained ferrite nanoparticles were studied by alternating current (AC) magnetic susceptibility measurement and electron paramagnetic resonance (EPR) spectroscopy. It was found that the un-substituted Mg ferrite sample exhibited microwave characteristics better than those of the Mn substituted and Mn-In co-substituted Mg ferrite samples.

Bismuth vanadate (BiVO₄), W-doped BiVO₄ (BiVO₄:W), and Mo-doped BiVO₄ (BiVO₄:Mo) nanoparticles were synthesized at pH = 4 using a green hydrothermal method. The effects of 2 at% W or Mo doping on the microstructural and optical characteristics of as-prepared BiVO₄ nanoparticles and the effect of combining particle morphology modification and impurity dopant incorporation on the visible-light-derived photocatalytic degradation of dilute Rhodamine B (RhB) solution are studied. XRD examination revealed that these obtained BiVO₄-based nanoparticles had a highly crystalline and single monoclinic phase. SEM and TEM observations showed that impurity doping could modify the surface morphology, change the particle shape, and reduce the particle diameter to enlarge their specific surface area, increasing the reactive sites of the photocatalytic process. XPS and FL measurements indicated that W- and Mo-doped nanoparticles possessed higher concentrations of oxygen vacancies, which could promote the n-type semiconductor property. It was found that the BiVO₄:W and BiVO₄:Mo powder samples exhibited better photocatalytic activity for efficient RhB removal than that shown by pristine BiVO₄ powder samples under visible light illumination. That feature can be ascribed to the larger surface area and improved concentration of photogenerated charge carriers of the former.