Hiraku Ogino

Hydrothermal synthesis of MoS2 nanowires

Abstract The MoS 2 nanowires with diameters of 4xa0nm and lengths of 50xa0nm were synthesized by a hydrothermal method using 0.36xa0g MoO 3 and 1.8xa0g Na 2 S as precursors in 0.4xa0mol/l HCl solution at 260°C. The products are characterized by XRD, XPS, TEM, HTEM and BET. Results show that the as-prepared MoS 2 nanowires consist of 1–10 sulfide layers with BET surface areas of 107xa0m 2 /g. The possible reaction route and the formation mechanism of the MoS 2 nanowires are discussed. The effects of exterior conditions such as pH value, temperature, concentration of precursors and additives on the particle size and morphology of MoS 2 crystallites were investigated.

Growth and scintillation properties of Pr-doped Lu3Al5O12 crystals

Abstract Pr-doped Lu 3 Al 5 O 12 (Pr:LuAG) single crystals were grown by the micro-pulling-down (μ-PD) method and Czochralski (Cz) method. The crystals were seeded-grown in the 〈1xa01xa01〉 direction. Dimensions up to 30xa0mm in length and 5xa0mm in diameter by μ-PD and up to 100xa0mm in length and 22xa0mm in diameter by Cz method were achieved. Concentration of Pr 3+ in Cz-grown Pr:LuAG was measured. Radioluminescence spectra and photoluminescence decay of Pr:LuAG were investigated and compared to Pr-doped Y 3 Al 5 O 12 (Pr:YAG) single crystals. Pr:LuAG crystals show better temperature stability of radioluminescence intensity and decay time compared to Pr:YAG, and luminescence was not quenched even at room temperature (RT). Scintillation light yield of Cz-grown Pr:LuAG was measured and compared to the standard BGO sample. Light yield of Pr:LuAG was more than two times higher than BGO and the relationship between Pr 3+ concentration and light yield was clarified.

Antisite defect-free Lu3(GaxAl1−x)5O12:Pr scintillator

Pr-doped Lu3(GaxAl1−x)5O12:Pr, x=0–1, single crystals were grown by the micro-pulling-down method. We study luminescence and scintillation characteristics of the sample set focusing on their dependence on the gallium content. For x=0.4 we obtain the high figure-of-merit material with elevated density, high efficiency, and very fast scintillation response below 20ns without any slower components. Improvement of scintillation performance is explained as due to the absence of the antisite LuAl defects that was for the first time realized in such bulk garnet single crystals grown from the high temperature melt.

Growth and optical properties of Yb doped new scintillator crystals

Abstract Single crystal of heavily Yb3+-doped Lu3Al5O12 (Yb:LuAG) were grown by the micro-pulling-down method. Radio- and photoluminescence spectra of the Yb:LuAG were studied. Two bands peaking round 340–350 and 480–500 nm could be ascribed to charge transfer (CT) luminescence of Yb3+, as their position nearly coincide with the Yb3+-related CT emission in YAG matrix. The highest emission intensity was observed for Yb concentration of 5% with respect to the Lu site. Temperature dependence of photoluminescence spectra of the Yb: LuAG (5%) was measured and points to remarkable thermal quenching above liquid nitrogen temperature.

Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses

Terahertz (THz) radiation generated from photoconductive antenna fabricated on a single crystal zinc oxide (ZnO) is presented. The THz-radiation power is saturated at bias voltages above 800V∕cm and the obtained spectrum extends up to 1 THz. Moreover, ZnO is found to be highly transparent in the visible, near-infrared, mid-infrared and THz frequency regions. The results depicted here will categorically unravel the prospects of using ZnO as a material for integrated active optics.

Crystal growth of Yb3+-doped oxide single crystals for scintillator application

Abstract Long emission wavelength scintillators are strongly required from the viewpoint of the practical use of silicon photo-diode, which has higher resolution with lower cost compared with photo-multipllier. Among the various scintillator emission centers, we regard emission from Yb 3+ charge-transitions state (CTS) as a candidate. In order to investigate proper hosts for Yb 3+ CTS, the yttrium gallium garnet host and lutetium aluminum garnet host were studied. Transparent and crack-free heavily Yb-doped YGG, i.e. {Y 1− x Yb x } 3 [Ga] 2 (Ga) 3 O 12 (Yb: YGG, x =0.15, 0.5, 1.0) and heavily Yb-doped LuAG, i.e. {Lu 1− x Yb x } 3 [Al] 2 (Al) 3 O 12 (Yb: LuAG, x =0.15, 0.5, 1.0) single crystals could be grown by the Modified Pulling Down method with 〈1xa01xa01〉 orientation. Emission, excitation spectra and decay kinetics were measured for these crystals. The CT transition of Yb 3+ in the yttrium gallium garnet host was discussed compared with the Yb 3+ one in the lutetium aluminum garnet host.

Growth and scintillation properties of Yb-doped Lu3Al5O12 crystals

Abstract Yb-doped Lu3Al5O12 (Yb:LuAG) single crystals were grown by the micro-pulling-down (μ-PD) method. The crystals were seeded-grown in the 〈1xa01xa01〉 direction and dimensions up to 300xa0mm in length and 5xa0mm in diameter were achieved. Photoluminescence spectra and decay kinetics of Yb:LuAG were studied after annealing. Under 225xa0nm excitation the double-peak emission at 335 and 480xa0nm was observed. Photoluminescence decay time of 23.9xa0ns was evaluated at 340xa0nm and T=80xa0K. Similar emission properties as those reported earlier for Yb-doped YAG crystal were obtained.

Study of finding DOI for a Pr:LuAG scintillator with a number of lateral grooves around the axis

A new method of finding the DOI for the PET/PEM device is proposed. The idea behind this is based on the conventional position finding method utilizing the light attenuation in a piece of scintillator. Stronger dependence of the signal pulse height along the scintillator length is more favorable without much degrading the energy resolution, and this can be realized by the present idea. To verify the expected performance, a number of scintillator samples of the recent advent, Pr:LuAG, were prepared: These were processed with 3 lateral grooves on their surfaces, whose depths were chosen preliminarily from 0.2, 0.4 and 0.6 mm. The tests were performed with LED or RI source such as Cs- 137, using a UV-sensitive PMT or a SiPM as the photo-sensor. A discrete attenuation behavior of the signal amplitudes was observed in each section separated by the groove(s), and this seemed to indicate the possibility of efficient detection of the DOI in any thickness of the scintillator used. The conventional dual-ends read out scheme is much simplified by reducing the number of scintillators. The single-end read out also will be promising if the material is heavy enough to dominate the total absorption over the scatter events.

Terahertz Radiation from Photoconductive Switch Fabricated from a Zinc Oxide Single Crystal

We present results on the terahertz (THz) radiation from a photoconductive switch fabricated on a zinc oxide (ZnO) single crystal. Due to its high transmittance in the visible, near-infrared, mid-infrared, and THz regions, ZnO may present itself as a viable material for integrated active optics operating in the THz region.

Scintillation properties of 2-inch-diameter Pr: Lu3A15O12 single crystal

Pr:LuAG has interesting properties of high density, high light yield and a very fast 5d-4f emission decay time. Recently we have develop 2-inch-diameter Pr:LuAG single crystal for scintillator applications such medical imaging and high-energy physics. In this report, we study uniformity of the light yield, energy resolution, decay time and gamma-ray response in the range from 59.5 keV (241Am) to 1.4 MeV (241Am).