[en] The optical properties of polyvinylpyrrolidone (PVP)-adsorbed and silica-coated Y₂O₃:Er,Yb nanoparticles produced by using PVP were studied for potential bio-applications of upconversion nanoparticles. We utilized PVP to better disperse Y₂O₃:Er,Yb nanoparticles in solution and to prepare silica-coated Y₂O₃:Er,Yb nanoparticles. The fluorescent intensity of PVP-adsorbed Y₂O₃:Er,Yb nanoparticles was 1.25 times higher than non-adsorbed Y₂O₃:Er,Yb nanoparticles, which was probably due to surface defects in Y₂O₃:Er,Yb nanoparticles being covered by the PVP. However, the fluorescent intensity of silica-coated Y₂O₃:Er,Yb nanoparticles decreased as silica layer thickness increased. This could be ascribed to the higher vibrational energy of PVP than that of the silica structure. Therefore, the optimum silica layer thickness is important in bio-applications to avoid deterioration of the optical properties of Y₂O₃:Er,Yb nanoparticles. - Highlights: • We prepared the silica-coated upconversion nanoparticles by using PVP. • We showed that PVP played an important role in coating nanoparticles. • PL intensity of silica-coated nanoparticles decreased as silica layer thickness increased

[en] We have achieved more than 1000 hours-operation in 266 nm-continuous wave (CW), 100 mW-generation of all-solid-state-UV laser system using Czochralski (Cz)-grown β-BaB₂O₄(BBO) crystal devices. Absorption of the Cz-grown crystal for e-ray at 266 nm was improved to 1%/cm, which is one-third lower than that of the crystal grown by top seeded solution growth (TSSG) method. Degradation rate of 266 nm generation, using 7 kHz repetition rate laser diode pumped Q switched Nd:YAG laser as a fundamental light source, was one order of magnitude lower than that of TSSG-crystal. Surface roughness of the crystal was better than 0.3 rms.-nm. HfO₂ film with extremely high adhesion was deposited on the surfaces using reactive low voltage ion plating method. Our devices can be put to practical use in areas of photolithography, micro fabrication, material processing and ultra high density optical disk mastering. (author)

[en] Up-conversion Gd${}_2$O${}_3$:Er,Yb nanoparticles (NPs) were fabricated by laser ablation in liquid, and the effect of laser irradiation time on their characteristics was investigated. The light source (a focused 532 nm second harmonic laser beam generated from a Nd:YAG laser) was used to irradiate the target pellet in water for 5, 15, or 30 min. Coarse NPs (> 200 nm) and fine NPs (< 100 nm) were observed. It is believed that the angular-shaped NPs resulted from fragmentation, and the spherical NPs were formed by laser melting or laser ablation in liquid (especially the < 80 nm particles). The main primary particle size range (25-75%), for the samples that had been irradiated for 5 min, was approximately 30-94 nm; for 15 min: 11-21 nm; and for 30 min: 11-24 nm. The secondary particle size decreased from 1000 to 200 nm with increasing irradiation time. The photon number was 2.3 for all the irradiation times. In every case, the zeta potential was above 15 mV, indicating a relatively stable dispersion. The transparency of the NP suspensions was almost the same for both the 5 and 15 min laser irradiation times, and higher than that of the 30 min suspension.

[en] We investigated the morphology of silicon nanoparticles prepared using laser ablation in liquid through varying the energy density and laser irradiation time. Silicon nanoparticles were prepared using laser ablation in liquid. A silicon wafer was irradiated in ethanol using a laser beam (Nd: YAG/second harmonic generation, 532 nm). Crystalline silicon nanoparticles approximately 6 nm in size were observed by TEM observation. The quantity of silicon nanoparticles proportionally increased with an increase in energy density greater than the laser ablation threshold. This quantity also increased with an increase in laser irradiation time without saturation due to absorption of the nanoparticles in liquid in the light path.

[en] The absorption of the ultraviolet-A (UVA), which causes imperceptible harm to human skin, was studied in CeO${}_2$ nanoparticles. The CeO${}_2$ nanoparticles with a high UVA ultraviolet absorption property were generated using laser ablation in the liquid approach without the use of any additives or surfactants. The properties of CeO${}_2$ nanoparticles were observed by controlling the concentration of nanoparticles, laser beam's energy intensity, and irradiation time. X-Ray Diffraction, Scanning Electron Microscopy (SEM), Dynamic Light Scattering (DLS), and Ultraviolet-Visible spectra were used to determine the morphology and optical properties. In this study, spherical CeO${}_2$ nanoparticles were dispersed in a suspension liquid with the sizes ranging from 5 to 50 nm using SEM and DLS observations. In addition, the absorbance in the wavelength range in UVA of the CeO${}_2$ nanoparticles-dispersed solution with the 200-400 nm waveband was first studied to show the potential of CeO${}_2$ nanoparticles as a UV-filtering material. In addition, the impact of laser irradiation on the spherical CeO${}_2$ nanoparticles' formation and their aggregation phenomena were discussed in this research and an approach for preparing CeO${}_2$ nanoparticles with spherical morphology was offered.

[en] Y_2O_3:Er,Yb nanoparticles were prepared by laser ablation in water. We investigated crystallinity, distribution of dopant, and optical properties of the prepared nanoparticles. The full-width half-maximum (FWHD) of the crystalline peak of nanoparticles measured by an x-ray diffractometer (XRD) barely changed. Further, using scanning transmission electron microscopy–energy dispersive x-ray spectroscopy (STEM–EDX), we confirmed the peaks of Y, Er, Yb, and O. Moreover, on the basis of the optical properties of the nanoparticles, the emission of red ("2F_9_/_2 → "4I_1_5_/_2) and green ("2H_1_1_/_2, "4S_3_/_2 → "4I_1_5_/_2) was confirmed. We also investigated the emission intensity as a function of the excitation power of 980 nm LD in the prepared nanoparticles. The photon avalanche effect was observed at the excitation power of 100 mW. These results confirmed that uniformly Er-Yb-doped Y_2O_3 nanoparticles were successfully prepared by laser ablation in water. (paper)

[en] With a focus on the temporal change of the earthquake resistant wall of building at Hamaoka Nuclear Power Station unit 1 reactor under decommissioning, this paper reports the test results on compressive strength, static elastic modulus, and density in the cross section of the earthquake resistant wall using concrete core samples obtained so far and the examination results of numerical analysis. The compressive strength distribution exceeded the design standard strength from the surface layer to the center part, and the central part particularly showed a high value, forming a so-called mountain type distribution. It is presumed that this was caused by drying from the surface and continuous hydration reaction inside the member. In the dry core sampling method that breaks off a predetermined long core, the compressive strength decreases in the central part of the member compared with the wet method or another dry method, and it is presumed that the temperature at the time of core collection gives influence. In the case of the dry method, it was confirmed that the method of breaking off each core pieces with a constant length is less affected by the temperature rise, and that the test result is about the same as that of the wet method. In the numerical analysis of temporal change of the concrete inside the member based on a hydration analysis model, the central part of the member showed a higher value than the surface layer in the long term, which could reproduce the tendency of the test data. (A.O.)

[en] Tc(III)-EDTA and Tc(III)-HEDTA complexes have been synthesized by the ligand substitution reactions of hexakis(thiourea)technetium(III) ion with EDTA and HEDTA. The compositions were identified as [Tc(III)(tu)Hedta]⁰, [Tc(III)(tu)₂Hhedta]⁺ and [Tc(III)(tu)hedta]⁰. The UV-Vis spectra of these complexes exhibited two absorption maxima at 368 and 470 nm, 377 and 493 nm, and 373 and 487 nm, respectively. The formation reaction proceeded predominantly in the following processes: Tc(tu)³⁺₆ + H₂edta → Tc(III)-EDTA (1) Tc(tu)³⁺₆ + Hhedta → Tc(III)-HEDTA (2) The rate constants for (1) and (2), determined at 25 C, were k = (2.1 ± 0.2) x 10^-1 M^-1s^-1 and k' = (3.2 ± 0.3) x 10^-1 M^-1s^-1, respectively. (orig.)

[en] Highlights: ► We prepared a Y₂O₃:Er,Yb nanoparticles by laser ablation in liquid. ► The particle size increased with the increasing energy density of the laser. ► At low energy density, dot-like nanoparticles were observed. At high energy density, worm-like nanoparticles were observed. ► In the photoluminescence spectra, green and red fluorescence were observed using a 980 nm laser diode as the excitation source. ► The fluorescence intensity increased with increasing energy density of the laser. - Abstract: We prepared a Y₂O₃: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 (²H_11/2, ⁴S_3/2 → ⁴I_15/2) and red (⁴F_9/2 → ⁴I_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.

[en] Highlights: • YVO4:Eu spherical nanoparticles were obtained by laser ablation in ethanol. • Crystallinity and optical properties of nanoparticles were analyzed. • Viscosity of liquid media is important for nanoparticle synthesis. - Abstract: YVO₄:Eu³⁺ nanoparticles were fabricated by pulsed laser ablation in water-ethanol mixtures with ethanol volume fractions of 0%, 10%, 30%, 50%, and 100%. Scanning electron microscopy and transmission electron microscopy were performed to characterize the nanoparticle morphologies and crystallinities. Photoluminescence and UV–vis absorption were used to investigate the optical properties. The results showed that only ovoid-like nanoparticles were obtained when using deionized water as the liquid medium. Sphere-shaped and ovoid-shaped nanoparticles simultaneously appeared after adding ethanol to the liquid; and finally, only spherical nanoparticles were obtained in pure ethanol. The crystallinities and PL intensities of the nanoparticles varied inversely to the corresponding liquid viscosity. When increasing the ethanol content, the UV–vis showed a blue shift that could be ascribed to the decreased covalence of V−O bonds.