Search

Abstract: ZnO nanoparticles (NPs) have been successfully synthesized by the chemical precipitation method in different atmospheres at 500°C. The annealing atmospheres were argon, forming gas (50% Ar/50% O2) and air, respectively. The effects of annealing atmosphere on the structure and optical properties of ZnO NPs were investigated in detail by X-ray diffraction, transmission electron microscope, photoluminescence and Raman scattering measurements. The results showed that the as-prepared ZnO NPs had a hexagonal wurtzite structure, and all the samples kept the overall crystal structure of bulk ZnO. From the Raman and photoluminescence spectra, it can be seen that the content of oxygen in different annealing atmospheres strongly influenced the crystallization and light emission of the ZnO NPs. The results revealed that the content of oxygen in air was the optimal condition for growing the ZnO NPs with the best crystalline quality and optical properties. Defect emission was significantly enhanced by annealing in Ar atmosphere, which indicated that the green defect emission was most likely due to oxygen vacancy. Moreover, the effect mechanism of annealing atmospheres on the structure and optical properties of ZnO NPs were also investigated. [Copyright &y& Elsevier]

Abstract: ZnO nanoparticles (NPs) have been successfully prepared by the chemical precipitation method at a low temperature of 200°C. X-ray diffraction (XRD), transmission electron microscope (TEM), photoluminescence (PL) and Raman were used to investigate the effect of annealing temperature on the structure and optical properties of ZnO NPs. The XRD analyses revealed that the average size of the as-prepared samples was about 8nm under 200°C, which had a good agreement with TEM images. Raman spectra showed that the E2 (high) mode became stronger and sharper with the increase of annealing temperature, but the intensity of phonon peak located at 580cm−1 was relatively suppressed. The position of ultraviolet (UV) emission peak in the room-temperature PL spectra showed a red-shift when the annealing temperature was increased. In addition, after annealing under 500°C, the intensity of the UV peak became strongest and the intensity of the green emission almost disappeared, which indicated that ZnO NPs have much better crystallization after annealing. [Copyright &y& Elsevier]

K 2 O–Na 2 O–Nb 2 O 5 –SiO 2 –B 2 O 3 glass-ceramics was prepared via melt-quenching and controlled crystallization route. To investigate the effect of crystallization treatment schedule on the dielectric properties of potassium sodium niobate (KNN) glass-ceramics, this report measured six glass samples with different crystallization treatment by XRD, SEM and LCR measurements. By means of changing heat-treatment schedule, it could be inferred that crystallization process and optimal treatment condition for KNN glass-ceramic with pore-free and high energy density. When the original glass samples crystallized at 707 °C for 2 h and 900 °C for 3 h, this crystallization treatment was beneficial to obtaining the glass-ceramic samples with purer perovskite structure K 0.1 Na 0.9 NbO 3 crystal phase and finer grains which possessed relative higher energy storage density (1.899 J/cm 3 ). The crystallization behavior and dielectric properties have exhibited a regular change at different crystallization temperature. Comprehensive results and analysis demonstrated that crystallization treatment played a role in dielectric properties of KNN glass-ceramics. In order to optimize energy storage, this experiment controlled transition from matrix glass phase of high breakdown strength (BDS) to ferroelectric crystal phase of high dielectric constant. [ABSTRACT FROM AUTHOR]

Abstract: Nanocrystalline samples of ZnS and Zn1−x Mn x S were synthesized by the solvothermal method without any surface-active agents and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), near-edge X-ray-absorption fine structure technique (XANES), photoluminescence (PL) and UV–vis. The results showed that the Mn2+ ions were substitutionally incorporated into the ZnS host and the size of the particles was decreased as the Mn doped-ratio increased. The yellow-orange emission from the Mn2+ 4T1–6A1 transition was observed in the PL spectra, the peak intensity ratio of which to that of sulfur vacancies increased with the increase of the Mn2+ concentration, and showed a maximum when the concentration of Mn2+ was kept at 3%. [Copyright &y& Elsevier]