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β-Ga2O3 is a well-known semiconductor material for power devices and other applications. Recently, β-Ga2O3 has also been reported as a scintillator material with a light yield of approximately 8400 ph./MeV, scintillation decay time of

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.

(Ce0.002 Y0.998−x Lu x )AlO3 (x = 0.000, 0.010, 0.100, 0.200) single crystals were grown and characterized to clarify the effects of Lu substitution in Ce:YAlO3 on its crystal structure, optical properties and thermal stability of Ce3+ luminescence. The lattice constants of (Ce0.002 Y0.798 Lu0.200)AlO3 were comparable to those of Ce:YAlO3, so the crystal structure was not significantly influenced by Lu substitution. Concerning the optical characterization, the absorption and emission spectra were almost the same regardless the amount of Lu substitution. This result is consistent with the assumption that the crystal field is not influenced by Lu substitution. The temperature dependences of the photoluminescence decay time showed that the quenching temperature (T 50%) tends to increase with the increasing Lu concentration. We conclude that the leading quenching mechanism is the thermally activated ionization which is suppressed by the Lu substitution in Ce:YAlO3.

We have grown Ce-doped (La,Y)$_2$Si$_2$O$_7$ single crystal by micro-pulling-down method and investigated its optical and scintillation properties. We have successfully prepared the single crystal with (Ce$_{0.015}$La$_{0.600}$Y$_{0.385}$)$_2$Si$_2$O$_7$ composition. The observed thermal quenching process could be characterized by the quenching temperature (T50%) of 526 K and its activation energy was determined to be 0.62 eV. Further considering the thermal quenching factors, it was found that the thermal quenching was caused by at least the thermal ionization and maybe also by classical thermal quenching. The light output and scintillation decay time were evaluated to be ~12,000 photons/MeV and ~42 ns, respectively. These results indicate that (Ce$_{0.015}$La$_{0.600}$Y$_{0.385}$)$_2$Si$_2$O$_7$ has a great potential for application in scintillation materials.

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.

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.

La2Zr2O7 crystals with a melting point of 2283 °C are grown via the micro-pulling-down (μ-PD) method using Mo and W crucibles to expand the possibility of material research of functional single crystals with high melting points by the μ-PD method. La2Zr2O7 crystals grown using Mo and W crucibles under an Ar + 3% H2 atmosphere are composed of a La2Zr2O7 main phase, which includes Mo and W. However, a La2Zr2O7 crystal without W can be grown under an Ar atmosphere using the μ-PD method using a W crucible and deoxygenated ZrO2 insulators. After post-annealing in air at 1000 °C, the La2Zr2O7 crystal without W becomes colorless and transparent, indicating a transmittance exceeding 70% in wavelengths ranging from 450 to 800 nm.

This research dealt with the investigation of luminescence properties of undoped and La doped Lu3Al5O12 single crystals using synchrotron radiation excitation. The influence of La3+ doping on the exciton emission and decay kinetics properties of Lu3Al5O12 single crystals was studied at 7 K and room temperature. Undoped and La3+ doped samples showed bright luminescence in the UV spectral range. In undoped Lu3Al5O12 crystal, the UV luminescence was associated with LuAl antisite defects, which acted as luminescence centers in the band peaked at 295 nm La3+ doping in Lu3Al5O12 crystals caused the formation of LaLu luminescence centers and increased the concentration of LuAl antisite defects. Therefore, the luminescence of La doped Lu3Al5O12 crystals was a superposition of the emission coming from both LaLu and LuAl centers. Furthermore, La3+ doping significantly enhanced the intensity and shifted the UV luminescence of Lu3Al5O12 crystals towards higher energy due to the dominant contribution of LaLu luminescent centers in the band peaked at 275 nm. The decay time of heavily La3+ doped LuAG crystals was also significantly accelerated due to the prevailing luminescence of LaLu centers.

Ce-doped (Gd, La)2Si2O7 scintillators have fast decay time and keep high light output even at high temperature (∼150°C). To improve the scintillation properties such as light output and decay time, Ce-doped (Gd, La)2Si2O7 scintillators codoped with the divalent ions (e.g. Mg2+, Ca2+) have been studied. In this study, we focused on the other divalent ions (Sr2+ and Ba2+), and investigated their effect on the scintillation properties and temperature dependence of light output. The absorption due to Ce4+ was not observed for Sr or Ba codoping. The light outputs were degraded by Sr2+ or Ba2+ codoping, while the decay times at room temperature were not changed for the samples codoped with divalent ions. On the other hand, the temperature dependence of light output for Ba-codoped sample was improved, and the light output value at 175°C was 36,000 photons/MeV, which was 93% of that at 25°C.

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.

(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.

The luminescence and scintillation properties of Gd1.53La0.47Si2O7:Ce (GPSLa23.5%:Ce) scintillators were investigated and compared to those of Lu1.9Y0.1SiO5:Ce (LYSO:Ce) scintillators. At 662 keV γ-rays, the light yield of 33,500±3300 ph/MeV obtained for GPSLa23.5%:Ce is higher than that of 28,100±2800 ph/MeV obtained for LYSO:Ce. The energy resolution of 4.8±0.2% obtained for GPSLa23.5%:Ce is much better than that of 8.2±0.3% obtained for LYSO:Ce due to its better intrinsic resolution and proportionality of light yield. The light yield and energy resolution for α- rays, as well as a light yield ratio under excitation with α - and γ - rays (α/γ ratio) were also determined. The intrinsic light yield and light loss coefficient under excitation with 662 keV γ-rays were evaluated. The total attenuation coefficient at 60 keV and 662 keV γ - rays was also determined and compared with the theoretical one calculated using the WinXCom program.

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.

The scintillation timing characteristics of (La,Gd)2Si2O7:Ce (GPSLa23.5%:Ce) single crystal were studied and compared with Gd2SiO5:Ce (GSO:Ce) single crystal. The photoelectron yield, scintillation decay times and coincidence time resolution were measured. At 511 keV γ-rays, the photoelectron yield of 10,770 ± 500 phe MeV−1 and energy resolution of 5.4 ± 0.2% obtained for GPSLa23.5%:Ce are much better than those of 3350 ± 160 phe MeV−1 and 7.8 ± 0.3% obtained for GSO:Ce. The scintillation decay time profile was measured by the time-correlated single photon counting technique using a fast-slow coincidence setup. In both materials the comparable rise times of several nanoseconds are present. The fast component decay time of 56 ns with relative intensity of 49% obtained for GPSLa23.5%:Ce is inferior to that of 32 ns(88%) obtained for GSO:Ce. Consequently, the coincidence time resolution of GPSLa23.5%:Ce is slightly worse than that of GSO:Ce. The normalized time resolution was also discussed in terms of a number of photoelectrons and decay time of the scintillation pulse.

(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.

The growth process, crystal composition, optical and scintillation properties of Lu3Al5O12:La (La = 0–0.45%) single crystals were investigated in detail. The thermodynamical stability of the garnet phase formation was studied in the undoped and La doped Lu3Al5O12 single crystals. The crystals were grown from the melt using a micro-pulling down method. Detailed composition analysis reviled the complex multiphase character of the samples. Both garnet and α-Al2O3 phases were detected in the undoped and slightly La-doped samples, while heavily La-doped crystals contained the mixture of α-Al2O3, garnet and perovskites phases. The substitution La for Lu led to the formation of LaLu centers and increased the concentration of LuAl antisite defects. Both types of centers caused a strong luminescence in the deep UV spectral range. Heavy La-doping significantly enhanced the scintillation performance of Lu3Al5O12 crystals.