Yuui Yokota

Shaped crystal growth of langasite-type piezoelectric single crystals and their physical properties

We have grown shape-controlled langasite-type crystals by the micro-pulling-down (μ-PD) method. Columnar shaped La₃Ta_0.5Ga_5.5O₁₄ (LTG), Ca₃NbGa₃Si₂O₁₄ (CNGS), Ca₃TaGa₃Si₂O₁₄ (CTGS), Sr₃NbGa₃Si₂O₁₄ (SNGS), and Sr₃TaGa₃Si₂O₁₄ (STGS) crystals were grown using a Pt-Rh crucible with a 3-mm-diameter columnar die at the bottom. All grown crystals showed high transparency except for the peripheral area and diameter of approximately 3 mm. The chemical phases at the central parts of the grown crystals were identified as a single phase of langasite-type structure and their lattice parameters were almost the same as those of crystals grown by the Czochralski (Cz) method; however, some impurity phases were observed in the peripheral area. In X-ray rocking curve measurements, the grown crystals indicated equivalent crystallinity to the crystal grown by the Cz method. The piezoelectric constant d₁₁ of the CNGS crystal was 3.98 pC/N; this value is well correlated with those of previous reports.

Growth and Luminescence Properties of Ce and Ca Co-Doped LiGdF4-LiF Eutectic Scintillator

Ce and Ca co-doped LiGdF4-LiF eutectics were grown and their directionally solidified eutectic (DSE) system has been investigated. In these eutectics, apart from the expected 305 nm emission of the regular Ce3+, 310 nm emission of the Gd3+ and Ce3+-perturbed emission around 320-380 nm was observed. Ce3+-perturbed emission at 340 nm shows the intrinsic decay time of about 27 ns. In photoluminescence mechanism the observed decay time shortening of the regular Ce3+ and Gd3+ centers point to the energy transfer in the sequence the regular Ce3+→ (Gd3+)n→ the perturbed Ce3+ sites.

Optical and Scintillation Properties of Cr Doped Y3Ga5O12 Crystal for Infra-Red Scintillators

We evaluated optical and scintillation properties of a Cr 0.5%:Y3Ga5O12 (YGG) and Cr 0.5%:Y3Al5O12 (YAG) crystals grown by the micro-pulling down method for infrared emission scintillators. In the photoluminescence and X-ray induced radioluminescence measurements, the emissions peaks of Cr:YGG were located in the longer wavelength than those of Cr:YAG. Radioluminescene spectrum of Cr:YGG had a broad peak at 716 nm related to Cr3+2E→4A2 and 4T→4A2 transitions.

Fundamental study of inorganic–organic hybrid scintillator using Pr:Lu3Al5O12 and plastic scintillator

Read out test of inorganic–organic hybrid scintillator; Pr:LuAG single crystal covered with plastic scintillator BC-499 is demonstrated. Emission peaks of the hybrid scintillator was observed around 430 nm, which suit to the sensitive wavelength of photomultiplier tube (PMT). The Pr:LuAG sample coated with BC-499 showed the better light output than the that of Pr:LuAG itself. Light output was increased up to 30% sing PMT (Hamamatsu R9800). Decay curve of the hybrid scintillator was also measured and successfully modeled. Corporation.

Annealing Effects for Ca3NbGa3Si2O14 Piezoelectric Single Crystals Grown by Micro-Pulling-Down Method

The langasite-type Ca3NbGa3Si2O14 [CNGS] piezoelectric crystals grown in Air and Ar were annealed under various temperatures and atmospheres and the effects of annealing on various properties were investigated. The absorption peaks around 360 and 500 nm of CNGS crystals grown in Air decreased by the annealing at 1300°C in Ar. On the other hand, the annealing at 1300°C in Air decreased transmittance in the range from 300 to 500 nm for the CNGS crystal grown in Ar. The results suggest that the absorptions around 350 and 500 nm originate from the excess oxygen and the post-annealing can control the oxygen content in the crystals.

Effects of Growth Atmosphere on Crystal Growth and Optical Properties for Ca3NbGa3Si2O14 Single Crystals

Ca3NbGa3Si2O14 (CNGS) single crystals were grown by the micro-pulling-down (μ-PD) method under various atmosphere, Air, Ar + 3%O2 and Ar 100%, and the effects of growth atmosphere on crystal growth and optical properties were investigated. While the CNGS crystal grown in Air indicated orange color, the crystal grown in Ar was colorless. CNGS crystal grown in Air indicated several large absorption peaks around 360 and 500 nm in the transmittance spectrum. In contrast, the crystal grown in Ar didnt indicate these absorption peaks.

TL Properties of Pure Al2O3 Grown by the Micro-Pulling down Method

Carbon-doped Al2O3 is used as a material for dosimeter using thermoluminescence (TL) technique or optically stimulated luminescence (OSL) technique, and the emission bands are originated from defect emission. We have an original crystal growth named micro-pulling down (μ-PD) method which had higher temperature graduation during the crystal growth. Thus, crystal defect is easy to be formed without some dopant using the μ-PD method. We grew pure Al2O3 samples with different heating condition, and different peaks in TL spectra were obtained among the pure Al2O3.