Optical properties of ZnO nanoparticles capped with polymers were investigated. Polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) were used as capping reagents. ZnO nanoparticles were synthesized by the sol-gel method. Fluorescence and absorption spectra were measured. When we varied the timing of the addition of the polymer to the ZnO nanoparticle solution, the optical properties were drastically changed. When PEG was added to the solution before the synthesis of ZnO nanoparticles, the fluorescence intensity increased. At the same time, the total particle size increased, which indicated that PEG molecules had capped the ZnO nanoparticles. The capping led to surface passivation, which increased fluorescence intensity. However, when PEG was added to the solution after the synthesis of ZnO nanoparticles, the fluorescence and particle size did not change. When PVP was added to the solution before the synthesis of ZnO nanoparticles, aggregation of nanoparticles occurred. When PVP was added to the solution after the synthesis of ZnO nanoparticles, fluorescence and particle size increased. This improvement of optical properties is advantageous to the practical usage of ZnO nanoparticles, such as bioimaging.
We prepared a Y 2 O 3 :Er,Yb nanoparticles by laser ablation in liquid. The laser used the second harmonic generation Nd:YAG (532 nm). A preparation process and measurement of upconversion properties were performed by varying the range of the energy density of the laser. Images from scanning electron microscopy (SEM) indicated that two types of nanoparticles existed in the product of laser ablation in liquid. We concluded the following: one type of nanoparticles was prepared from the nucleation of materials in a plume and the other was prepared by fragmentation. In the photoluminescence spectra, green (2 H 11/2 , 4 S 3/2 → 4 I 15/2) and red (4 F 7/2 → 4 I 15/2) fluorescence were observed using a 980 nm laser diode (LD) as the excitation source. We confirmed that the fluorescence intensity increased with increasing energy density of the laser. Thus, we concluded that the number of the nanoparticles increased as the energy density of the laser was increased.
Using containerless processing with an aerodynamic levitation furnace, LaO3/2–TiO2 binary glasses were synthesized in bulk form. Glass‐forming region was found in the vicinity of eutectic point, which is approximately 29.5% LaO3/2 and 70.5% TiO2 in molar ratio. The glass transition temperature Tg and the crystallization onset temperature Tx of the obtained glasses were determined by differential scanning calorimetry. The thermal stability was evaluated by ΔT (=Tx − Tg). Our experimental results were compared with phase diagram of the LaO3/2–TiO2 binary system. Glass compositions with highest ΔT corresponded to single‐phase compound of La4Ti9O24 and the eutectic point.
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