---

In this work, KTiOPO₄ nanoparticles were synthesized by both hydrothermal and coprecipitation methods and studies were carried out on their structural and optical properties. To study the physical properties of samples, XRD, FT-IR, UV-Vis and FE-SEM analyses were used. Hydrothermal method, using different starting materials, resulted to the production of finner particles (9.6 nm and 12.54 nm) compared with nanoparticles (34.65 nm) produced by coprecipitation method.

---

In this research, ZnO nanorods were grown via hydrothermal method on the glass substrate. The effect of precursor and the thickness of the seed layer on the structural and optical properties of grown ZnO nanorods were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and UV-vis spectroscopy. The XRD patterns indicated that the nanorods had wrutzite hexagonal crystalline structure with orientation of [002]. FESEM images clearly revealed that the ZnO nanorods with different solution concentration on different seed layers and precursor solution concentration were grown on substrate glass. The ZnO nanorods with solution concentration of 50 mM and 10 times the seed layer deposition are the better morphology and more optical transmittance in the range of visible. So this sample could be a suitable candidate for electron transport layer on inverted polymer solar cells.

---

In this research, the Dysprosium stannate nanostructured compound (Dy₂Sn₂O₇) is prepared as an important spin ice compound. In the synthesis of this compound, from a solution of 0.1 mol of Tin (IV) chloride pentahydrate (SnCl₄; 5H₂O) with the addition of Dysprosium (Dy (NO₃)₃.xH2O) nitrate with molar ratios equal to [Dy / Sn] = 0.1, 0.3, 0.5, 0.7 and 0.1 were used to prepare Dysprosium stannate nanocrystals (Dy₂Sn₂O₇) by hydrothermal method. The effect of Dysprosium (Dy) with different percentages on the formation of Dysprosium stannate composition by annealing at T= 1100 ° C in normal environment was investigated. The structural and optical properties of the formed compound were investigated. The results of X-ray diffraction (XRD) patterns of the sample annealed at T=1100 ° C showed the formation of nanocrystals in the pyrochlore structure of the Dysprosium stannate with [Dy / Sn] =1. The results of visible-ultraviolet (UV-Vis) spectroscopy showed that the energy gap increases with increasing Dysprosium additive. Field Emission Scanning Microscope (FE-SEM) images confirm the formation of Dysprosium stannatenanocrystals with pyrochlore structure.

---

In this paper, the nanoparticles of FeNi₃ were prepared by hydrothermal and co-precipitation methods. Also, different times and temperatures with different amounts of the hydrazine reducing hydrate were investigated in hydrothermal method. After fabrication of the samples by two methods, the samples have been characterized using the x-ray diffraction analysis (XRD), the field emission scanning electron microscopy (FESEM), and magnetic properties of the samples using a vibrating sample magnetometer (VSM). The results of diffraction pattern show that the amount of hydrazine hydrate used is very effective in single-phase sampling. FESEM images show nanoparticles, but at some temperatures and times, particles are not formed or stickiness and melting are observed. The results of VSM analysis show that the samples have high magnetic properties in both methods and not much change in saturation magnetization between samples was seen in both methods.
 

---

In this study, ZnO, α-Fe₂O₃ and ZnO/Fe₂O₃ nanocomposites powders with weight ratios of (1:0/.5), (1: 1) and (1: 2) were prepared using hydrothermal method and their structural, optical and magnetic properties were investigated. The results obtained from analysis of the XRD patterns confirmed formation of the hexagonal structures for ZnO and Fe₂O_3. The absorption spectra of the synthesized samples showed that the absorption in the visible region increases for ZnO/Fe₂O₃ nanocomposite and its band gap value reduces (increases) in comparison to the zinc oxide (iron oxide). FESEM images showed that Fe₂O₃ spherical nanoparticles are located on the surface of the ZnO nano-sheets .The results obtained from magnetic studies by VSM revealed that ZnO has a diamagnetic property and α-Fe₂O₃ shows soft ferromagnetic behavior and for the nanocomposites, the magnetization values increase with increasing the Fe₂O₃ concentration. In general, the results show that the particle size, optical property and magnetic property of the ZnO/Fe₂O₃ nanocomposites strongly depends on the concentration of Fe₂O₃.

---

In this research, pure and doped with Dy³⁺ and Gd³⁺ ions, as impurity of La₂(WO₄)₃ nanoparticles, were successfully synthesis using hydrothermal method and the effect of annealing temperature, type and concentration of dopant on their structural and optical properties were investigated and used as down converter material in dye sensitized solar cell. The samples were characterized by X-ray diffraction, field emission scanning electron microscopy (equipped with spectra energy dispersive analysis of X-ray), transmission electron microscopy, ultraviolet-visible spectrometer and photoluminescence spectrometer. The X-ray diffraction results showed that the nanoparticles are polycrystal with monoclinic structure. Optical studies show that these nanoparticles can absorb ultraviolet light and emit visible light in the wavelength ranging from 360 nm to 500 nm. The presence of a thin layer of La₂(WO₄)₃:Dy nanoparticles on the dye sensitized solar cell increased the efficiency by 10.6%.