Search

This study presents the criteria for shape control in the micro-pulling-down (μ-PD) method for low-wettability systems (dewetting μ-PD method), which enables us to achieve highly shape-controllable crystal growth. In the dewetting μ-PD method, the presence of the die wall inhibits the direct observation of the meniscus during the process. Therefore, in this study, the meniscus shape was calculated using the Young–Laplace equation to predict the optimal crystal growth conditions. The free-end and fixed-end boundary conditions to be satisfied for the differential equations were defined at the triple point, with the melt on the die wall. The relationship between the crystal diameter and pressure in the fixed-end condition, wherein the wetting angle (α) at the triple point of the crystal was 90°, indicated the suppression of the melt infiltration by the presence of crystals. The gap between the die and crystal was minimized for the contact angle (θ) and growth angle (αgr) in the fixed-end and free-end conditions, at which |αgr + θ – π| was minimum at a given pressure under the assumption of single-valued solutions. The results of this study will facilitate the formation of noble-metal alloys with a net shape and expand the scope for the development of new materials.

We propose a novel crystal growth method, “Core Heating (CH) Method”, which is suitable for a search of novel materials with extremely high melting points above the melting (softening) point of an ...

GdTaO4 and (Gd1-xTbx)TaO4 (x = 0, 0.001, 0.02, 0.04, 0.10, and 0.16) single crystals were grown by the micro-pulling down method. The crystallographic system of the grown crystals was identified to be monoclinic (I2/a), which is the stable low-temperature phase of GdTaO4. In the photoluminescence (PL) spectra, intense emission was observed at 549 nm (5D3→7F4 transition of Tb3+) for every Tb doped GdTaO4. In the excitation spectra for the 549 nm emission, several excitation paths to the Tb3+ were attributed: 4f-4f transitions of Gd3+, 4f8-4f75d transitions of Tb3+ and charge transfer of TaO43− group. Radiolumincece spectra under X-ray irradiation were taken, and the highest emission peak was observed at 544 nm, which was ascribed to the 5D4→7F5 transition of Tb3+. The Tb 2% doped GdTaO4 showed the highest emission intensity at the 544 nm, and as increasing dopant concentration, the intensity decreased due to the cross-relaxation of Tb3+.

Ce-doped LaBr3/AEBr2 (AE = Mg, Ca, Sr, Ba) eutectics were grown using the Bridgman&ndash, Stockbarger (BS) method in quartz ampoules. The eutectics (AE = Mg and Ca) showed optical transparency like optical fiber bundles. A grown Ce-doped LaBr3/MgBr2 eutectic shows a 355 nm emission ascribed to Ce3+ 4f-5d transition under X-ray excitation. The smaller the ionic size of AE, the higher the light yield of the sample was. The light yield of Ce:LaBr3/MgBr2 was 34,300 photon/MeV, which is higher than Ce:LYSO standard. Scintillation decay time under 662 keV gamma-ray excitation was 18.8 ns.

A novel single-crystal growth method was developed, using arc plasma and metal melt, for a quick survey of high melting point materials. Single crystals of Yb-doped Lu2O3, Lu0.388Hf0.612O1.806, and Lu0.18Hf0.82O1.91, with melting points of 2460, 2900, and 2840 &deg, C, respectively, were grown by an indirect heating method using arc plasma. We refer to this indirect heating growth method as the core heating (CH) method. The CH-grown Yb1%-doped Lu2O3 sample showed a full width at half maximum of 286 arcsec in the X-ray rocking curve. This value is better than the 393 arcsec obtained for the crystal grown by the micro-pulling-down (&mu, PD) method. The Yb charge transfer state (CTS) emission was observed at 350 nm in the Yb1%-doped Lu2O3 and Lu0.18Hf0.82O1.91. In the case of the &mu, PD method, using a rhenium (Re) crucible, absorption due to Re contamination and a resulting reduction in the Yb CTS emission were confirmed. However, contamination did not influence the properties observed in the crystals grown by the CH method.

Ce-doped (Gd, La)2Si2O7 (Ce:La-GPS) scintillator was found to have a good light output of around 40 000 photons/MeV, while some other parameters have not been determined so far. In order to clarify the cause for such a high light yield, some physical parameters have been estimated in this paper. The bandgap energy of Ce:La-GPS was evaluated to be over 7.13 ± 0.03 eV for (Gd0.75, La0.25)2Si2O7. Although Ce:La-GPS had wider bandgap compared with the other oxide scintillators, its light output was larger than values for some other scintillators. Since quantum yield of Ce:La-GPS was as high as around 0.8, the product of transfer efficiency and electron–hole pair generation efficiency was estimated to be around 0.9, which was higher than for the other scintillators. Thus, Ce:La-GPS was suggested to have high the product of transfer efficiency and/or electron–hole pair generation efficiency.

Single crystals of (La0.25Gd0.75)2Si2O7 and (La0.235Ce0.015Gd0.75)2Si2O7 were grown by the Czochralski method. Structure analysis of the single crystals by X-ray diffraction (XRD) revealed that (La0.25Gd0.75)2Si2O7 and (La0.235Ce0.015Gd0.75)2Si2O7 crystalize in monoclinic cells (space group P21/c), a = 5.3905(8) A, b = 8.5605(11) A, c = 13.957(2) A, β = 112.223(6)o, and a = 5.3921(7) A, b = 8.5688(10) A, c = 13.9172(14) A, β = 111.980(5)o, respectively. One of the two different rare-earth sites is preferentially occupied by La and Gd atoms or by La, Ce and Gd atoms, and the other is occupied by Gd atoms only. Peaks attributed to the 4f-4f transitions (8S7/2–6G7/2 and 8S7/2–6Ix) of Gd3+ and 4f-5d transitions of Ce3+ were observed in the absorption spectra of (La0.25Gd0.75)2Si2O7 and (La0.235Ce0.015Gd0.75)2Si2O7 single crystals.

This paper addresses several aspects of the µ-PD growth technology as applied to submillimeter diameter sapphire tubes for UFD application. The μ-PD method has been successfully adapted for single crystal sapphire tube growth. A compound crucible made possible the growth of single crystal sapphire tube as small as around 0.70–0.72 mm in outer diameter and 0.28–0.29 in inner diameter over 160 mm in length at growth rate of 2–4 mm/min along 〈0 0 1〉 direction. An Ir crucible with a die composed of an equivalent hole and Ir wire was heated by RF coil in N2 atmosphere. The μ-PD method has been successfully adapted for single crystal sapphire tube growth. Grown crystal tube showed good XRC value of 30.2 arcsec.

The fabrication and thermal electromotive force characteristics of Ir/Ir-Rh thermocouples capable of repeated bending deformation are described. Ir and Ir-Rh wires with a diameter of 0.5 mm were fabricated using the alloy-micro-pulling-down method. Scanning electron microscopy and electron backscattering diffraction of the radial cross section of the grown wires were performed to investigate the microstructure and orientation of the crystal grains. At the start of growth, the microstructure was polycrystalline with diameters of several hundred micrometers, while at the 8-m growth point it was found to be monocrystalline. The observed single crystals of pure Ir and Ir-Rh alloy were oriented in the 〈1 1 3〉 and 〈1 1 2〉 directions, respectively, whereas the polycrystalline Ir-Rh samples showed preferential growth in the 〈1 0 0〉 direction. The thermal electromotive force of the fabricated Ir/Ir-Rh thermocouple was measured by the comparison technique and the fixed-point technique, and the thermoelectric power was estimated to be 5.9 μV/°C in the range from 600°C to 1100°C.

Ce-doped (Gd, La) 2 Si 2 O 7 scintillation crystals are expected to be used as gamma-ray detectors for high temperature measurement. To realize scintillators for high temperature environment, we investigated (Ce 0.01 Gd 0.59−x La 0.40 Y x ) 2 Si 2 O 7 (x = 0.00, 0.05, 0.10, 0.15) single crystals grown by the micro-pulling-down method. The results showed that a 5% Y-admixed Ce-doped (Gd, La) 2 Si 2 O 7 scintillator can yield higher light output when compared with Y-free Ce-doped (Gd, La) 2 Si 2 O 7 scintillator. The light outputs at 25°C and 175°C were determined to be ∼43,000 and ∼40,000 photons/MeV, respectively. Moreover, 1 inch size 5% Y-admixed Ce-doped (Gd, La) 2 Si 2 O 7 scintillator was grown by the Czochralski technique, and its light output at 175°C kept the value of around 95% of the value at 25°C.

A 6LiCl/6Li2SrCl4 eutectic scintillator with a high Li concentration was developed as a novel thermal neutron scintillator. Eu2+ served as an activator for the 6Li2SrCl4 phase, and Eu-doped 6LiCl/6Li2SrCl4 eutectics were grown via the Bridgman Stockbarger method in quartz ampoules (inner diameter = 4 mm). The Eu-doped 6LiCl/6Li2SrCl4 eutectics exhibited a lamellar-type eutectic structure and optical transparency, as well as 400 nm emission due to Eu2+ 5d-4f transition. The scintillation properties of the eutectics were evaluated under gamma- and alpha-ray irradiation to demonstrate its potential as a thermal neutron scintillator.

Iridium, ruthenium, and iridium-ruthenium alloy wires were fabricated by the dewetting micro-pulling-down method, a type of unidirectional solidification method. The length of the grown Ir-20Ru reached 47 m. Furthermore, their mechanical and thermoelectric properties were investigated. The as-grown Ir-17.9Ru wire exhibited a tensile strength of approximately 765 MPa and a nominal fracture elongation of 21% at room temperature. After work-hardening by three cycles of winding and rewinding for a bending radius of 10 mm and annealing at 2273 K for 3 h, the tensile strength and fracture elongation of the Ir-Ru wire were 1061 MPa and 25%, respectively. From the electromotive force (EMF) characteristics of platinum obtained by integrating the Seebeck coefficient, the EMF characteristics from room temperature to ~ 2000 K of iridium, ruthenium, and Ir-17.9Ru were investigated. The EMF characteristics for several thermocouples using iridium, ruthenium, or Ir-17.9Ru as one of the pairs were estimated from the combination of the obtained EMF characteristics. Ir/Ir-17.9Ru showed similar EMF characteristics to Ir-40Rh/Ir.

In this study, one-inch diameter Tl:CsI/CsCl/NaCl eutectic scintillators were grown by the Czochralski method at various pulling rates. Crystal growth conditions such as rotation, pulling rates, and crystal growth setup were analyzed. By examining the structure of the obtained eutectic, the growth orientation of the CsI phase as well as the optimum pulling speed and rotation speed were found. A transparent eutectic plate of about 3 × 5 mm was prepared from the grown sample, and scintillation properties such as light output and decay time after excitation by 662 keV gamma-rays were evaluated. The performance was compared with the Tl: CsI single crystal standard. Furthermore, a β-ray imaging test was carried out by combining the eutectic plate and an electron-multiplied charge coupling device camera, and the position resolution as an imaging device was evaluated.

The development of a real-time dose monitor system is one of the important issues in medical engineering to reduce medical accidents such as overdose or incorrect positioning of the treated human tissue during radiation therapy. One of the challenging solutions is to use an infrared scintillator, which is sufficiently bright so that the light can be detected outside the human tissue. In this study, a novel infrared scintillator, Cr-doped Gd 3 Ga 5 O 12 , was tested with pork meat as a phantom of human tissue to prove its feasibility for the dose monitor. The scintillation photons of Cr:Gd 3 Ga 5 O 12 were observed through even 50-mm thick pork meat. The emission peak originated from d-d emission of Cr 3+ . The emission intensity of Cr:Gd 3 Ga 5 O 12 was approximately 3.5 times larger than that of the conventional infrared scintillator Cr:α-Al 2 O 3 . Moreover, we succeeded in performing the infrared imaging for Cr:Gd 3 Ga 5 O 12 irradiated with alpha-rays using a complementary metal oxide semiconductor camera.

Ce-doped Lu 2 Si 2 O 7 scintillator contains radioactive isotope 176 Lu which causes an unwanted intrinsic background signal. The development of scintillators with reduced Lu concentration were required in some applications. In this study, we developed the Gd admixed lutetium pyrosilicate, where the average ion radius at the rare earth site was similar to the Tm 3+ ion radius, for which the RE 2 Si 2 O 7 (RE=Tm, Yb, Lu) crystal structure is stable from room temperature to melting point. We have grown (Ce x Lu 1−x−y Gd y ) 2 Si 2 O 7 (x=0.01, y=0.00, 0.05, 0.10) single crystals. Their crystal systems were monoclinic with a space group C 2/ m . The absorption spectra revealed the energy transitions in Ce and Gd ions might be occurred. The light output was degraded and decay time was accelerated comparing the Gd 5% admixed sample with the Gd 10% one.

In this study, Eu and Ce doped LiSrI3 single crystals were explored and the scintillation performance was reported at the first time. Eu and Ce doped LiSrI3 single crystals were grown by the Bridgman–Stockbarger method in a quartz ampoule with 3 mm inner diameter. Growth rate was 0.06 mm/min. Circular samples with 1 mm thickness were obtained from the grown crystal. The grown Eu doped LiSrI3 crystal demonstrated Eu2+ 4f–5d emission peak at 420 nm under alpha-ray excitation. In the case of Ce doped one, double emission peaks at 360 and 400 nm were observed. The light yield of the Eu doped LiSrI3 was around 35,000 photon/MeV for 662 keV gamma-ray and 24,000 photon/5.5 MeV for alpha-ray. Energy resolution of the Eu doped LiSrI3 was 5.2%@662 keV. Scintillation decay time of the grown Ce and Eu doped LiSrI3 under 662 keV gamma-ray was 23.8 ns (50%) 212 ns (50%) and 545 ns 100%, respectively.

(Ce0.01 Gd0.59 La0.40)2Si2O7 single crystal (La40% sample) was grown by the micro-pulling-down method to study its scintillation properties and their temperature dependence. In addition, we investigated the relation between these properties and La concentration comparing the crystal with (Ce0.01 Gd0.90 La0.09)2Si2O7 (La9% sample). As results, the light output of the La40% sample at 25°C was similar to that of the La9% sample. On the other hand, the decay time of the La40% sample was slower than that of the La9% sample at 25°C. The light output of La40% sample had a small decrease rate at high temperature when compared with that of La9% sample.

Growth of 2-in. diameter Ce-doped (La , Gd) 2 Si 2 O 7 (La-GPS) scintillating crystals by Czochralski method using Ir crucible is reported. The composition of the host material was approximately equal to La 0.5 Gd 1.5 Si 2 O 7 and the concentration of the Ce 3+ -activator was either 0.5 or 1.5 at.% with respect to the total content of the rare-earths forming the host crystal matrix. Effects of the hot zone construction including inductive coil position, presence/absence of the after-heater, rotation rate and other growth parameters on the crystal quality are discussed in some details. The crystals produced in optimized conditions were colorless, transparent, uniform in their shape, crack- and inclusions-free, and demonstrated smooth glass-like surface. The length of the crystals’ cylindrically-shaped body parts exceed 100 mm. The growth results were well reproducible. The main disadvantage of the growth process is associated with short lifetime of the Ir crucible and its deformation caused by thermal expansion of the pre-solidified melt at each heating stage.

(CexYb1−x)2Si2O7 (x = 0.00, 0.01) single crystals were grown by the micro-pulling-down method to test the possibility of its application as infra-red scintillator for medical imaging. Powder X-ray diffraction analysis indicated that the crystals were single-phase materials. The radioluminescence spectra of the crystals demonstrated presence of two near infra-red emission peaks (at 1010 and 1030 nm). The emission peaks at 420 and 580 nm ascribed to defects were also observed in the crystals. The human body has maximum transmission in wavelength range from 650 to 1200 nm. Therefore, Yb2Si2O7 is expected to be used as efficient infra-red scintillator for medical applications.

(Gd 0.75 ,Ce 0.015 ,La 0.235 ) 2 Si 2 O 7 (Ce:La-GPS) single crystals co-doped with 0, 100, 200, 500 and 1000 ppm Zr were grown by the Czochralski process, and their scintillation properties were investigated. We investigated the co-doping effect of a stable tetravalent ion in Ce:La-GPS for the first time. The scintillation decay times in the faster component were shortened with increasing the Zr concentration. While the non-co-doped sample showed ∼63 ns day time, the Zr 100, 200, 500 and 1000 ppm co-doped samples showed ∼61, ∼59, ∼57, ∼54 ns, respectively. Additionally, light output, photon nonproportional response (PNR) and other optical properties were investigated.

1300 or 1400 °C pre–sintered Al/Ce/Mg:SrHfO 3 and Al/Ce:SrHfO 3 ceramics were prepared by the Spark Plasma Sintering (SPS) in order to search for a new scintillation material with a high–effective atomic number(Z eff ) and good light output. The SrHfO 3 has a high Z eff of 60, and high gamma–ray detection efficiency is expected. Meanwhile it has a high melting point of over 2500 °C, and single crystal is hard to be grown. On the other hand, high melting materials can be prepared as ceramics, and the SPS method is a simple process to fabricate the ceramics within a few hours. Thus, we prepared the samples using the SPS method, and their optical and scintillation properties were investigated. We found that Al/Ce/Mg:SrHfO 3 and Al/Ce:SrHfO 3 ceramics had an emission wavelength at around 400 nm originating from 5d–4f transition of Ce 3+ . Moreover, Al/Ce/Mg:SrHfO 3 pre-sintered at a temperature of 1400 °C had a light output of approximately 5,000 ph/MeV. In this paper, the light output of Mg-co-doped samples was improved compared with the Mg-free ones. The light output also depends on the pre-sintering temperature.

Edge defined Film Fed Growth (EFG) method with molybdenum (Mo) crucible and die was studied for the growth of several oxide-based single crystals. At first, reactivity between the molybdenum (Mo) metal and oxide melts of Ce:(Lu,Y)2SiO5 (LYSO) Ce:Y2SiO5 (YSO), Ce:Gd3(Al,Ga)5O12 (GAGG), Ce:Lu3Al5O12 (LuAG), Ce:Y3Al5O12 (YAG) was investigated. The experimental and calculation results on the reactivity with Mo show that the aluminum garnets (LuAG, YAG) had the smallest reactivity with Mo metal. On the contrary, GAGG showed the strongest reaction with Mo. Then, the multiple-die grown shaped single crystal growth of Ce:LuAG was demonstrated by EFG method. Single crystal plates up to 320 mm in length were grown successfully. The homogeneity of dopant distribution, Mo contamination, luminescence and scintillation responses of the grown crystals were evaluated.

(Eu 0.01 , Gd 0.90 , La 0.09 ) 2 Si 2 O 7 (Eu:La–GPS) and (Tb 0.01 , Gd 0.9 0 , La 0.09 ) 2 Si 2 O 7 (Tb:La–GPS) crystals were grown by the floating zone method, and their optical and scintillation properties were investigated. Gd 3+ -to-Tb 3+ or –Eu 3+ energy transfer processes were found, and photo-luminescence and radio-luminescence emission spectra showed 5 D 0 – 7 F i ( i = 1–4) Eu 3+ transitions in Eu:La–GPS, and 5 D 3 – 7 F i ( i = 3–6) and 5 D 4 – 7 F i ( i = 3–6) transitions in Tb:La–GPS. Using these scintillators, alpha-ray imaging was possible with a CMOS camera. These materials can be used for X-ray detection as well.

Ce:Gd2Si2O7/SiO2 eutectic was grown by the μ-PD method. The square-shape sample with a side of 5 mm and a length of 15 mm was obtained. Two phases of orthorhombic Gd2Si2O7 and SiO2 was observed. Rod-phase was SiO2 and matrix phase was Gd2Si2O7. Ce3+ 4f5d emission have been observed at 400nm. The sample showed light yield of around 16,000 photons/MeV. Scintillation decay time was 46.3ns(21%) 249ns(79%).