Herein, n-type pure and Zn²⁺-doped monoclinic bismuth oxide nanoparticles were synthesized by the citrate sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) analysis, ultraviolet-visible (UV-vis) spectroscopy, and Hall effect measurements were used to study the effect of Zn²⁺ on the structural, optical, and electrical properties of nanoparticles. XRD revealed the monoclinic stable phase (α-Bi₂O₃) of all synthesized samples and the crystallite size of nanoparticles increased with increasing concentration of dopant. Optical analysis illustrated the red shift of absorption edge and blue shift of band gap with increasing concentration of dopant. Hall Effect measurements showed improved values (2.79 × 10^-5 S cm^-1 and 6.89 cm²/V·s) of conductivity and mobility, respectively, for Zn²⁺-doped α-Bi₂O₃ nanoparticles. The tuned optical band gap and improved electrical properties make Zn²⁺-doped α-Bi₂O₃ nanostructures promising candidates for optoelectronic devices. The degradation of methylene blue (MB, organic dye) in pure and zinc-doped α-Bi₂O₃ was investigated under solar irradiation. The optimum doping level of zinc (4.5% Zn²⁺-doped α-Bi₂O₃) reveals the attractive photocatalytic activity of α-Bi₂O₃ nanostructures due to electron trapping and detrapping for solar cells.

Owing to its low resistivity, high transmittance, and tunable optical band gap, ZnO is of great interest for optoelectronic applications. Herein, the sol–gel technique was used to synthesize un-doped and zirconium-doped zinc oxide (ZZO) nanostructures with different concentrations of Zirconium (Zr). X-ray diffraction (XRD), scanning electron microscope (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), UV-Vis spectroscopy, and photoluminescence (PL) measurements were used to investigate the influence of Zr doping on the structural, optical, and electrical properties of developed nanostructures. XRD and SEM confirmed the increase in crystallite size with increasing concentrations of Zr. Raman analysis indicated the presence of oxygen vacancies in synthesized nanostructures. UV-Vis spectroscopy illustrated the blue shift of band gap and red shift of the absorption edge for ZZO nanostructures with increasing concentrations of Zr. For the measurement of electrical properties, the spin-coating technique was used to deposit un-doped and Zr-doped ZnO layers of ~165 nm thickness. The four-probe-point (4PP) method illustrated that the doping of Zr caused a reduction in electrical resistance. Hall Effect measurements showed a high value, 3.78 × 10²⁰ cm⁻³, of the carrier concentration and a low value, 10.2 cm²/Vs, of the carrier mobility for the Zr-doped layer. The high optical transmittance of ~80%, wide band gap of 3.51 eV, low electrical resistivity of 1.35 × 10⁻³ Ω·cm, and maximum carrier concentration of 3.78 × 10²⁰ cm⁻³ make ZZO nanostructures one of the most promising candidates for the application of transparent conductive oxide (TCO) in optoelectronic devices.

Zinc sulfide (ZnS) thin films with variable structural, optical, electrical, and thermoelectric properties were obtained by changing the source-to-substrate (SSD) distance in the physical-vapor-thermal-coating (PVTC) system. The films crystallized into a zinc-blende cubic structure with (111) preferred orientation. The films had a wide 3.54 eV optical band gap. High-quality homogenous thin films were obtained at 60 mm SSD. The sheet resistance and resistivity of the films decreased from 10¹¹ to 10¹⁰ Ω/Sq. and from 10⁶ to 10⁵ Ω-cm, when SSD was increased from 20 mm to 60 mm, respectively. The phase and band gap were also verified by first principles that were in agreement with the experimental results. Thermoelectric characteristics were studied by using the semi-classical Boltzmann transport theory. The high quality, wide band gap, and reduced electrical resistance make ZnS a suitable candidate for the window layer in solar cells.