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Effects of the tungsten (W) ions co-doping on the crystal growth, optical and scintillation properties for the Czochralski (Cz) grown Ce:Gd3Ga3Al2O12(GGAG) single crystals were investigated. The W 0%, 0.1%, 0.3%, 1%, and 5% co-doped Ce 1%:GGAG single crystals with a diameter of 1 in and length of 60–80 mm were grown by the Cz method. The effective segregation coefficient of the W ions was found as 0.002, 0.001, and 0.005 for W 0.1%, 0.3%, and 1%, Ce:GGAG, respectively. The segregation of W ions in GGAG host, light yield, and scintillation decay of the W co-doped Ce:GGAG were evaluated. The light yield decreased as the concentration of W co-dopant increased and toward the tail of the crystal. Furthermore, the defect role and related charge trapping in the W co-doped crystals were monitored by the thermo-stimulated luminescence.

Се-doped (Pb,Gd)3(Al,Ga)5O12 single crystalline garnet films were grown using liquid-phase epitaxy from four series of supercooled PbO–B2O3-based melt solutions on Gd3Ga5O12 and Gd3Al2.26Ga2.74O12 single crystal substrates. The optical and scintillation properties of the epitaxial garnet films were studied. The 5d-4f emission of Ce3+ ions within 450–650 nm was observed. The highest pulsed cathodoluminescence yield and scintillation yield values under 133Ba excitation for the Pb0.01Ce0.02Gd2.97Al3.13Ga1.87O12 film were 43,100 photons/MeV and 20,000 photons/MeV, respectively. The pulsed cathodoluminescence decay times of the film were 1.8 (1%), 24 (25%), and 60 ns (74%), and the scintillation decay times were 3.9 (7%) and 43.6 ns (93%). Because of the rapid decay and high light yield, Се-doped (Pb,Gd)3(Al,Ga)5O12 garnet films can be used in X-ray scintillators for different applications, such as homeland security.

In this study, optical-guiding crystal scintillator (OCS) and bundled plates were fabricated. Considering the performance and melting point of halide scintillators and the softening point of glass, Tl:CsI was selected as the fiber core and borosilicate glass as the cladding. Thus, the fabricated OCS had a scintillator in the core and glass in the cladding. The scintillator was remelted and unidirectionally solidified to remove the voids in the OCS and form a single crystal. Consequently, the OCS served as a scintillator fiber with excellent optical-guiding performance and high sensitivity to γ- and X-rays. An OCS plate was also fabricated using bundles of OCSs with diameters of several tens of microns. The developed OCS plate is expected to be a high-resolution and high-sensitivity imaging plate because of its excellent optical-guiding performance.

Scintillation properties of a flexible optical-guiding crystal scintillator with a thallium-doped CsI (Tl:CsI) crystal and borosilicate glass as the core and cladding, respectively, are reported. The as-fabricated optical-guiding crystal scintillator exhibits a light yield of 31,000 photons MeV−1 under 662 keV γ-ray irradiation. The recrystallized sample is transparent and provides a higher light yield of 54,000 photons MeV–1, which is comparable to that of single-crystal Tl:CsI. The decay times are 400 ns (28%) and 1,350 ns (72%). This material can serve as a scintillator fiber with high sensitivity to γ- and X-rays, high light yield, and energy discrimination.

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.

In this study, Eu:6LiCl/BaCl2 with a high Li concentration was developed as a novel thermal neutron scintillator. Eu ions were doped as activators for the BaCl2 phase, and Eu:6LiCl/BaCl2 eutectics were grown via the vertical Bridgman–Stockbarger method in quartz ampoules (inner diameter = 4 mm). The Eu:6LiCl/BaCl2 eutectic exhibited a lamellar eutectic structure and optical transparency. The 400 nm emission due to the Eu2+ 4f–5d transition was observed in the BaCl2 phase by a cathode luminescence measurement. The light yield under neutrons was estimated to be over 20 200 photons MeV−1. A PSD study was also performed using gamma and alpha-rays. The Eu:6LiCl/BaCl2 eutectic scintillator showed good potential for PSD.

A 6LiBr/CeBr3 eutectic thermal-neutron scintillator, with a high 6Li concentration, was developed using the vertical Bridgman method. The grown eutectic contained an 6Li molar ratio of 35%, which is higher than those of the commercial neutron scintillators such as Ce:LiCaAlF6 and Ce:Cs2LiYCl6. Furthermore, it showed optical transparency and a lamellar eutectic structure elongating along the growth direction. The synthesized eutectic showed emission peaks at 360 and 380 nm, originating from the Ce3+ 5d-4f transition in the CeBr3 scintillation phase. The scintillation performance of 6LiBr/CeBr3 was evaluated under X-ray, γ-ray, and neutron irradiation to corroborate its neutron detection potential.

In this study, a large-size eutectic scintillator of Tb-doped BaCl2/NaCl/KCl was grown using the Czochralski (Cz) and halide vertical Bridgman methods (H-VB). The suitability of these two growth methods for growing the eutectic was compared. Finally, 1 inch diameter eutectic bulks were obtained using the H-VB method. The Tb3+-derived strongest intensity peak at approximately 550 nm was observed by X-ray irradiation. An approximately 3 × 3 mm transparent eutectic wafer was cut and polished from the grown eutectic bulk. An imaging test using α-ray was performed using the grown eutectic, a fiber optic plate, and an electron-multiplying CCD camera. The resolution performance for radiation-imaging applications was evaluated.

Ce0.5%: Ce:Gd3Ga3Al2O12(GGAG) single crystals co-doped with 500at.ppm Li+, Na+ and K+ were grown by using the micro-pulling down method. The smooth Ce4+ charge transfer absorption below 350 nm and decay time acceleration were observed in Li co-doped sample. Na+ and K+ co-doping did not show a large effect on the acceleration of decay time compared with Li co-doping. Ce0.5%:GGAG single crystals co-doped with 500 at.ppm Li+ were also grown by the Czochralski method. Optical, scintillation properties and timing performance were evaluated to investigate the effect of univalent alkali metal ions co-doping on Ce:GGAG scintillators. The scintillation decay curves were accelerated by Li co-doping: the decay time was significantly accelerated to 54.8 ns (47%) for the faster component and 158 ns (53%) for the slower component. The light output was 94% of the non co-doped Ce:GGAG standard. The coincidence time resolution was improved to 258 ps by Li co-doping.

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.

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.

Melt growth of scintillating halide crystals is reviewed. The vertical Bridgman growth technique is still considered as very popular method that enables production of relatively large and commercially attractive crystals. On the other hand, the micro-pulling-down method is preferable when fabrication of small samples, sufficient for preliminary characterization of their optical and/or scintillation performance, is required. Moreover, bulk crystal growth is also available using the micro-pulling-down furnace. The examples of growths of various halide crystals by industrially friendly melt growth techniques including Czochralski and edge-defined film-fed growth methods are also discussed. Finally, traveling molten zone growth that in some degree corresponds to horizontal zone melting is briefly overviewed.

In this study, Tl:CsI/KI/KCl eutectic scintillators were grown using the Bridgman–Stockbarger method by unidirectional solidification. The eutectic phases were uniformly distributed in the transverse direction and were slightly aligned along the growth direction. The Tl:CsI scintillator phase was grown as a matrix, which was then used for creating optical waveguides of the scintillation light. The expected Tl+ emission peak was observed at 486 nm under X-ray excitation and cathodoluminescence; this was attributed to the self-trapped exciton perturbed by TI+ in Tl:CsI. The decay time of the Tl:CsI/KI/KCl eutectic was 313 ns, and its light output was estimated to be 22,000 photons/MeV.

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.

Ca 3 Ta(Ga 1- x Al x ) 3 Si 2 O 14 [CTGAS] material is a piezoelectric material belonging to the Langasite-type group (space group: P321).and the CTGAS single crystals ( x =0, 0.25, 0.50, 0.75) with a diameter of 1 in. were grown by a Czochralski [Cz] method using an Ir crucible under Ar+2%O 2 . The CTGAS single crystals without any cracks could be grown using a CTGAS seed crystal in the x range of 0≤ x ≤0.75. Cell parameters, a and c , decrease while the a / c ratio increased with the Al concentration. Piezoelectric constant d 11 and electromechanical coupling factor k 12 for the X-cut specimens of the CTGAS single crystals were increased by the Al substitution.

1 in. diameter Mg 0.05, 0.1, 0.2, 0.5 mol% and Zr 0.015% co-doped Ce1%:GGAG crystals were grown by Cz method. Relationship between Mg concentration and absorption, luminescence, light output, decay time, timing resolution was investigated. Mg 0.2 mol% co-doped sample showed the fastest timing resolution of 165 ps among the Mg-co-doped samples.

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.

The influence of the composition of Tb-Sc-Al garnet crystals (TSAG) on the value of Verdet constant was investigated at the wavelengths of 400–1060 nm. It was found that this value increased both, with the decrease of Sc3+ ions content and with the decrease of lattice parameter. The value of Verdet constant of TSAG crystals depend on lattice parameter value and increased from 0.168 to 0.198 min/(Oe cm) (at λ = 1064 nm) with the decrease of Sc3+ ions content from 1.76 to 1.3 f.u. The value of Verdet constant for TSAG crystals with Sc3+ ions content of 1.3 f.u. can be described using one- and two-oscillator models with the same accuracy. The absorption at the wavelengths of 226 and 272 nm for the sample with a thickness of 13 μm was observed and wavelengths were used for calculations of Verdet constant in accordance with the two-oscillator model.

The 2 inch size Li 0.15 and 1.35 mol% co-doped Ce:Gd 3 Al 2 Ga 3 O 12 single crystals were prepared by the Czochralski (Cz) method. Absorption and luminescence spectra were measured together with several other scintillation characteristics, namely the scintillation decay and light yield to reveal the effect of Li co-doping. Ce 4+ CT absorption below 350 nm is clearly enhanced by Li co-doping as same as divalent ions co-doping. By 1.35 at.% Li co-doping, light yield was decrease to 88% of the Ce: GAGG standard and decay time was accelerated to 34.3ns 21.0%, 84.6ns 68.7%, 480ns 10.3%. The timing resolution measurement for a pair of 3 × 3 × 3mm 3 size Li,Ce:GAGG scintillator crystals was performed using Si-PMs and the timing resolution of the 1.35 at.% Li co-doped Ce:GAGG was 218ps.

Wafers of Tb-doped GdAlO3/α-Al2O3 eutectic were fabricated by the micro-pulling-down method using an Ir crucible with a 25 × 25 mm2 die. A prototype X-ray phase imaging detector was developed using a CMOS sensor with a fiber optic plate and the eutectic wafer. X-ray spots with an 8.24 μm period were observed using the detector. X-ray phase imaging of a nylon ball with a diameter of 4 mm was also carried out. It was observed that a phase change of approximately 2 μm occurs at the air–nylon interface. This technique of X-ray phase imaging can be realized in the absence of an absorption grating.

Tl:CsI/CsCl/NaCl eutectic scintillators were grown by the Bridgman–Stockbarger method. The eutectic phases were uniformly distributed in the transverse direction and slightly aligned along the growth direction. Then, the CsI phase can be designed as columnar. The expected emission peak observed at 550 nm was observed under X-ray excitation and cathodoluminescence and was ascribed to the self-trapped exciton perturbed by TI+ in Tl:CsI. The mapping of optically waveguided light emission was observed by confocal laser microscopy, consequently optical waveguiding of Tl+ emission in the CsI phase was demonstrated.

A vertical Bridgman (VB) crystal growth process was established using modified micro-pulling-down (μ-PD) crystal growth system with a removable chamber that was developed for the growth of deliquescent halide single crystals because conventional μ-PD method does not allow growth of large bulk single crystals. Eu:SrI2 crystals were grown from the melt of (Sr0.98Eu0.02)I2 composition using carbon crucibles. Undoped μ-PD SrI2 crystals were used as seeds that were affixed to the bottom of the crucible. All the preparations preceding the growths and the hot zone assembling were performed in a glove box with Ar gas. Then the removable chamber was taken out of the glove box, attached to the μ-PD system, connected with a Turbo Molecular pump, and evacuated down to 10−4 Pa at ~300 °C. After the baking procedure, high purity Ar gas (6N) was injected into the chamber. The crucible was heated by a high frequency induction coil up to the melting point of Eu:SrI2. After melting the starting materials, the crucible was displaced in downward direction for the crystal growth and then cooled down to room temperature. Thus, 2 in. and crack-free Eu:SrI2 bulk crystals were produced. The crystals had high transparency and did not contain any visible inclusions. The crystals were cut and polished in the glove box and then sealed in an aluminum container with an optical window for characterization. The details of the crystal growth are discussed.

The 3 in. size Ce1%:Gd 3 Al 2 Ga 3 O 12 single crystals were prepared by the Czochralski (Cz) method. Optical constants were measured. Chemical composition analysis and uniformity of scintillation decay and light yield along growth direction were evaluated. The timing resolution measurement for a pair of 3 mm×3 mm×3 mm size Ce:GAGG scintillator crystals was performed using Si-PMs.

Growth of 2-in. diameter Al-substituted Ca 3 TaGa 3 Si 2 O 14 crystals by Czochralski method is reported. The crystals were grown from the melt of Ca 3 TaGa 1.5 Al 1.5 Si 2 O 14 composition and had langasite structure. No inclusions of secondary phases were detected in these crystals. The Ca 3 Ta(Ga,Al) 3 Si 2 O 14 mixed crystals produced using non-substituted Ca 3 TaGa 3 Si 2 O 14 seeds were defective. They had cracks and/or poly-crystalline structure. However, those grown on the seed of approximately Ca 3 TaGa 1.5 Al 1.5 Si 2 O 14 composition were defect-free. Phase diagram of the Ca 3 TaGa 3 Si 2 O 14 –Ca 3 TaAl 3 Si 2 O 14 pseudo-binary system and segregation phenomenon are discussed in some details. Homogeneity of the crystals was evaluated by measuring 2D-mapping of leaky surface acoustic wave (LSAW) velocities for Y -cut Ca 3 TaGa 1.5 Al 1.5 Si 2 O 14 substrate. Although some inhomogeneities were observed due to slight variations in chemical composition, the crystal had acceptable homogeneity for applications in acoustic wave devices exhibiting the LSAW velocity variation within ±0.048%.

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.

Single crystal scintillators are extensively used in various radiation detection applications and their scintillation performances can be improved via co-doping. Therefore, in this study, tungsten-ion co-doped Ce:Gd3(Ga,Al)5O12 (Ce:GGAG) crystals were grown using the micro-pulling-down (μ-PD) method to investigate the effects of co-doping on their scintillation properties. The relationships between the W concentration, optical and luminescence properties, and radiation response of the W-co-doped Ce:GGAG crystals were evaluated. The W-co-doped Ce 0.5%:Gd3Ga3Al2O12 single crystals of diameter 3 mm and length 30–60 mm were grown by the μ-PD method. The light yield increased at W concentrations of 200 and 500 ppm and decreased at W concentrations above 1000 ppm. There was no significant change in the fast decay component of scintillation.

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.

Ce-doped Gd3Al2Ga3O12 single crystals 4 in. in diameter were grown by the Czochralski technique. Three main growth problems were identified: formation of Ir particles on the surface of the melt, Ga oxide evaporation and crystal cracking during the cooling stage. These problems were solved by careful selection of the ceramic hot zone, shift of the growth atmosphere from Ar + O2 to N2 + CO2 and application of an original post-growth cooling technique. It was found possible to grow up to five sequential 4-inch crystals from the same melt without any notable decrease in the scintillation properties. The optimal solidification fraction (0.23) was found. Additionally, a 4-inch Mg,Ce co-doped Gd3Al2Ga3O12 crystal was grown under the same conditions.

Time-of-flight Positron emission tomography (TOF-PET) is one of the next-generation medical imaging methods, which requires scintillators with a very short decay time. However, the shortest scintillation decay times are typically 20–30 ns, and these values are not sufficient for TOF-PET. Cherenkov counters are used in high energy physics and they are expected to be applied in medical imaging due to their short decay time. Here, high-refractive index materials are necessary for Cherenkov radiators to reach a high light output. We measured refractive indices of Gd3Ga5O12 (GGG), Y3Ga5O12 (YGG) and Lu3Ga5O12 (LuGG) crystals grown by a micro-pulling-down ( μ - PD ) method. The GGG, YGG and LuGG crystals were found to have refractive indices of ~ 2.5 , ~ 2.3 and ~ 2.3 at 400 nm, respectively. Then we grew a 40 mm diameter GGG crystal by the Czochralski method, and the emission decay times of the GGG crystals irradiated with muons and gamma rays were 10 ± 1 ns and 10 ± 2 ns , respectively, using a photomultiplier tube (Hamamatsu R6231-100). Cherenkov light of the GGG crystal could be observed for the gamma-ray irradiation.

10%-Ce doped GdScO3 perovskite type single crystal was grown by the Czochralski process. The Ce concentration in the crystal was measured. No impurity phases were observed by powder X-ray diffraction analysis. We evaluated the optical and radiation properties of the grown crystal. Ce:GdScO3 crystal showed photo- and radio-luminescence peaks due to Ce3+ of 5d-4f transition and colour centre. The photoluminescence decay time was sub-ns order. The relative light yield under 5.5 MeV alpha-ray excitation was calculated to be approximately 9% of BGO. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical and scintillation properties of a 1.0-mol% Dy-doped yttrium aluminium garnet (YAG) grown under N2 atmosphere and undoped YAG crystals were investigated. Both crystals were grown by the Czochralski process. The one of the undoped YAG crystal was grown in an Ar + H2 (97:3) reducing atmosphere. Absorption peaks at 352 nm and 366 nm observed in 1.0-mol% Dy-doped YAG originated from 4f-4f transition of Dy3+. In addition, the crystal showed sharp emission lines at near 482 nm and 584 nm under 352 nm UV and alpha-ray excitation. The light output of Dy-doped YAG was estimated to be approximately 20,000 photons/(5.5-MeV alpha ray, 241Am). The scintillation decay time constants for Dy-doped YAG crystal was around 400 ns and 40 ns. Undoped YAG crystals grown under Ar + H2(97:3) atmosphere showed absorption and excitation peak at 370 nm. A 400-nm emission peak was observed under 370-nm excitation. The light output of the crystal was also estimated to be 50,000 photons/(5.5-MeV alpha ray). The scintillation decay time constants of the crystal were around 370 ns and 50 ns. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

HfO2 Has High Effective Atomic Number and No Radioactive-Isotope as the Background Source, and it Can Be the Candidate for the High-Stopping Scintillator Instead of Lu2SiO5:Ce Scintillator Used in Medical Imaging, Astronomy and etc. However, HfO2 Has an Extremely High Melting Point of 2774 °C, and it Is Difficult to Grow the Crystal from the Melt Using Crucible, as there Is No Suitable Metals, which Can Survive around that Temperature. Thus, Czochralski, Bridgman, and Micro-Pulling down Method Cannot Be Applied. Therefore we Investigated Optical Properties of a 17-mol% b-Doped (Stabilized) HfO2 Crystal Grown by the Skull Melting Method, and this Crystal Had a High Refractive Index of 2.5 at 550 nm, and the Maximum Emission Peak at ~550 nm from 5D4 Excited States of Tb3+. In Addition, we Found the Radiation Reaction of the Crystal Irradiated with Alpha and Gamma Rays Measuring with a Photomultiplier.

Optical and scintillation properties of YVO4, (Lu0.5Y0.5)VO4, and LuVO4 single crystals grown by the Czochralski (CZ) method with RF heating system are compared. All vanadate crystals show high transmittance (∼80%) in the 400–900 nm wavelength range. In both photo- and radio-luminescence spectra, intense peak around 400–500 nm, which was ascribed to the transition from triplet state of VO43−, was clearly observed. The main decay time component was about 38 μs (YVO4), 18 μs ((Lu0.5Y0.5)VO4), and 17 μs (LuVO4) under 340 nm excitation. The scintillation light yields of YVO4, (Lu0.5Y0.5)VO4, and LuVO4 crystals (obtained from the 137Cs excited pulse height spectra) were evaluated to be about 11,200, 10,700, and 10,300 ph/MeV, respectively.

We evaluated optical and scintillation properties of a 0.03% Cr-doped Gd3Ga5O12 (GGG:Cr) single crystal grown by Czochralsk method for medical use. Since human body has low absorption region from approximately 700-1100 nm, near infrared scintillators would be applied to the real time dose monitor system. In the X-ray excited radioluminescence, the emissions related to 2E → 4 A2 transitions of Cr3+ were observed at around 725 nm. The scintillation light yield of GGG: Cr 0.03% single crystal under 5.5 MeV alpha-ray excitation was determined to be 30% of BGO.

Undoped and neodymium-doped (1 at %) gadolinium vanadate (GdVO4) single crystals 5 mm in diameter and up to 25 mm in length, uniform in cross section, have been grown by the micropulling down method. The chemical and phase compositions of the crystals have been determined, and their absorption spectra were measured.