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Indium doped zinc oxide (In:ZnO) nanostructures were synthesized using the refluxed sol-gel method at pH levels of 7, 8, 9, 10, 11 and 12 for the precursor solution, adjusted by the addition of aqueous sodium hydroxide to the solution mixture of zinc and indium salts. X-ray diffraction (XRD) patterns revealed intense diffraction peaks of wurtizite In:ZnO nanocrystals with increased broadenings due to the incorporation of larger size In3+ ions to the lattice sites of Zn2+ ions. The substitution process of the dopant ions into the lattice sites and the size of the crystallites were influenced and facilitated by the pH of the solution. The crystallite size decreased from 23 nm to 19 nm with an increase of pH level of the precursor solution. The micrograph from field emission scanning electron microscopy (FE-SEM) showed an aggregated mixture of spindle- and cone-like morphology which decreased in size as the solution pH increased. Transmission electron microscopy (TEM) also confirmed the morphology and the decrease in size of the structures obtained by FE-SEM measurements. The UV–Vis reflectance analysis also demonstrated that the optical properties of In:ZnO crystallites improved with the increase in pH of the solution, as shown by the blue shift of the absorption edge of the reflectance spectra. The energy band gap increased nearly linearly from 3.22 eV to 3.26 eV with the increased pH values from 7 to 12 which was attributed to the Burstein-Moss effect. Photoluminescence (PL) measurements show a significant change in the emission characteristics. Both excitonic and defect level emission bands were shifted to shorter wavelength as the pH level increased, verifying the widening of the energy band gap. The relative intensity ratios of excitonic to defect level emission bands (INBE/IDLE) decreased generally as the pH level increased, indicating the increased concentration of the defects of oxygen interstitials and vacancies in the produced nanostructures. All measurements exhibited in this study confirmed that increasing the alkalinity of the synthesis solution enhanced the production of highly crystalline In-doped ZnO nanostructures for a better and suitable material in the area of biomedical, solar cell and other optoelectronics applications.

Nanocrystalline ZnO were synthesized using refluxed sol-gel method by varying the co-solvent volume ratio of methanol to water (MeOH:Water) from 0:1 to 1:0 with step of 0.2, respectively. It is known that solvent type and ratio significantly affect the morphology, structural and luminescence properties of ZnO. All the produced ZnO samples have nanoneedle, rod, sheet, spherical and nanoplate like mixed morphology and pure highly crystalline hexagonal wurtzite structure. The crystallite size varies from 22.2 to 26.7 nm with an increase in the amount of methanol in a co-solvent from 0:1 to 1:0 and the average lattice parameters are calculated as a = b = 3.246 A and c = 5.202 A. The room temperature PL measurement results showed that both near band gap emission (NBE) at around 380 nm and deep level emission (DLE) in the yellow-green region centered at 530 nm are displayed with an excitation NeCu laser source of wavelength 248.6 nm. The ratio of the intensity of NBE to DLE decreases as the amount of the methanol increases in the solvent. The NBE emission band of the prepared ZnO samples were blue shifted and the emission energy center increased from 3.237 to 3.263 eV as methanol amount increased in the co-solvent. The free and donor-bound excitonic emissions were also studied using low temperature PL measurements and quantum the quenching effects are observed from the results. Primary and secondary longitudinal (LO) phonon replica of the bound excitons also observed during low temperature PL measurements. The optical band gaps of the produced samples determined from UV–Vis reflectance measurements decreased as methanol volume increased in the co-solvent.

Doped ZnO nanoparticles were synthesized using sol-gel method, with simultaneous incorporation of Gallium (Ga) and Indium (In). The structural, chemical, optical an luminescence properties of the pure, single doped and co-doped (GaInZnO) nanostructures were characterized by X-Ray diffraction (XRD), EXD Field Emission Scanning Electron Microscopy (FESEM), UV–vis spectroscopy, and Photoluminescence spectroscopy. XRD disclosed that the produced nanostructures were pure and single phase hexagonal wurtzite in structure. The diffraction peaks of the co-doped sample was seen to shift slightly towards lower diffraction angle values as compared to pure ZnO. The calculated crystallite sizes significantly varied between 21.9 and 8.2 nm depending on the dopant ratios. All synthesized samples show excellent optical properties with more than 85 % reflectance in the visible region. The energy band gap of the crystals were observed to shrink with co-doping than undoped and single doping. The PL results also revealed the typical UV and visible emission band patterns with a slight shift to the lower wavelength for the co-doped samples. The proper co-doping of In and Ga is therefore expected to provide a broad range optical and physical properties of ZnO nanostructures for a variety of optoelectronic applications.

Indium-doped zinc oxide (In:ZnO) nanocrystals are successfully produced by a simple refluxed sol-gel technique. The influence of post-heat treatment/ annealing temperatures on the structure, morphology, optical and luminescence properties of nanostructures was investigated using X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), energy dispersion X-ray spectroscope (EDS), UV–Vis and photoluminescence spectroscopies (PL). The XRD results revealed that the synthesized In:ZnO materials are nanocrystalline with a predominant hexagonal wurtzite structure. The average crystallite sizes and lattice constants of the In:ZnO nanoparticles increase with an increase in annealing temperature. SEM micrographs confirmed the nanostructure of the material and showed that the morphologies of In:ZnO nanoparticles varied from prism-like to spindle-like and then to disk-like structures. The reflectance band edge shifted towards longer wavelength while the band gap energy decreased with an increase in annealing temperature. In addition, the PL spectra show a sharp UV and broad yellow-orange emissions in the visible range that shifts slightly due to the influence of annealing temperature. The results illustrate that an optimum property of In:ZnO nanomaterial can be produced when the samples are annealed in the temperature range of 500 to 600 °C.

ZnO nanoparticles were synthesized using refluxed sol–gel method with variable zinc precursor concentration ranging from 0.1 to 0.2 M. The structural, morphology and optical properties of ZnO nanostructures were investigated using different characterization techniques. Concentration of zinc precursor significantly affects the morphology, structural and optical properties. All ZnO samples prepared are pure hexagonal wurtzite in structure and the crystallite sizes increases from 24 to 35 nm. The average lattice parameters were calculated as a = 0.3267 nm and c = 0.5232 nm. The average bond length of ZnO nanocrystalline was calculated to be around 0.1988 nm. The photoluminescence measurement result shows that both UV (at 380 nm) and visible (between 428 and 636 nm centered at 540 nm) emissions are displayed with the excitation wavelength of 248.6 nm from NeCu laser source. The room temperature photoluminescence measurement shows that the emission wavelength shifted towards the higher wavelength as zinc precursor concentration increases. The intensity ratio of the near-band-edge emission to deep-level emission increases as zinc precursor concentration increases. With low temperature photoluminescence (from 84 to 300 K) measurement, the emission energy increases from 3.28 to 3.35 eV. The deep-level emission of the ZnO was displayed in the green and yellow regions of the visible spectrum. The reflectance spectra from UV–Vis spectroscopy show that the concentration of zinc precursor has a significant effect on the band gaps of the material which decreased from 3.26 to 3.24 eV as the zinc precursor concentration increased from 0.1 to 0.2 M.