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Growth and Optical Characterization of Europium and Cerium Doped KCl Single Crystals by Czochralski Method for Dosimetric Applications
摘要： Rare-earth-doped alkali halide single crystals KCl:Eu, KCl:Ce, and KCl:Eu,Ce were grown from melt using the Czochralski technique, and optical characterization was carried out with the prime focus on dosimetric applications. The grown crystals were investigated using XRD analysis, PL analysis, TSL measurements, and OSL measurements. The XRD of the crystals matched well with ICDD patterns (00-041-1476), and diffraction peaks can be assigned to the KCl structure, indicating that all the crystals have the same structure as KCl. The enhanced intensity of TSL and OSL was observed for co-doping of (Eu, Ce) in KCl crystals as compared to single doping. The appearance of a single glow peak in KCl:Eu,Ce at 230°C compared to single-doped KCl:Ce crystals suggested the use of the material in TL dosimetry. The intensity of OSL also showed a two-fold increase compared to single-doped crystals, suggesting its use in OSL dosimetry. PL studies showed a very high enhancement of intensity in Eu2+ emissions, reaching a maximum of about 421 nm in the (Eu2+, Ce3+) co-doped crystal compared to single-doped crystals. This justifies the occurrence of energy transfer from Ce3+ to Eu2+ in the KCl host lattice. These results showed that KCl:Eu,Ce acts as a potential TL and OSL dosimeter due to its high sensitivity to ionizing radiation.
关键词： crystal growth,Single crystal,potassium chloride,optical characterization,Czochralski method
更新于2025-09-23 15:23:52
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Effect of crucible and crystal rotations on the solute distribution in large size sapphire crystals during Czochralski growth
摘要： In this study, the ?ow, temperature and solute concentration ?elds in the melt during the CZ growth process are numerically investigated. The results show that the magnitude and distribution of the solute concentration in the melt is strongly affected by the convective ?ow and thermal distribution. The maximum solute concentration always occurs at the crucible sidewall where the maximum temperature in the melt is found and the solute concentration at the crystal-melt interface increases from the triple point to the centerline. Heat transport from the side crucible wall towards the crystal-melt interface is enhanced by the crucible rotation. The level of the solute concentration inside the melt is reduced due to the lowering of the maximum temperature at the crucible wall. As a consequence, the distribution of the solute concentration along the crystal-melt interface becomes smaller and more uniform as the crucible rotation rate increases. However, after the crucible rotation rate becomes large enough, the maximum solute concentration and the solute concentration along the crystal-melt interface start to increase. Heat transport inside the melt is also affected by the crystal rotation. The centrifugal force induced by the crystal rotation generates a vortex below the crystal-melt interface. This vortex gets larger and stronger as the crystal rotation rate increases. In the smaller crystal rotation rate regime, this vortex is very small, suppressing the solute concentration at the crystal-melt interface. Therefore, the solute concentration along the crystal-melt interface becomes less when the crystal rotation rate is higher, although there is an increase in the maximum solute concentration in the melt due to the higher maximum temperature. In the higher crystal rotation rate regime, there is a reduction in the convexity of the crystal-melt interface due to enhancement of heat transport from the bottom wall of the crucible by vortex motion under the crystal-melt interface. Therefore, there is a switch to an increase in the transport of solute impurities into the crystal-melt interface. Hence, the solute concentration along the crystal-melt interface increases as the crystal rotation rate increases. However, with a further increase in the crystal rotation rate, as the shape of the crystal-melt interface changes becoming concave towards the melt, the solute concentration along the crystal-melt interface decreases because the maximum temperature is signi?cantly reduced. In this study, both counter- and iso-rotations are considered. The results of a comparison of the cases of iso- and counter-crystal rotation show that the lowest and most uniform solute distribution along the crystal-melt interface is achieved when there is no crystal rotation and the crucible rotation rate is ?xed at 1 rpm. In other words, the lowest and most uniform solute concentration can be achieved with the only crucible rotation.
关键词： Solute concentration,Czochralski method,Sapphire,Numerical simulation,Crucible and crystal rotations
更新于2025-09-23 15:21:21
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Growth and investigation of Sm3+-doped GLSO crystal for visible laser application
摘要： In this study, a mixed Sm3+-doped Sm0.02Gd1.88La0.1SiO5 (Sm:GLSO) laser crystal was grown successfully by Czochralski method. The structure of the as-grown crystal was determined with X-ray diffraction. The as-grown crystal exhibits large absorption cross section (1.53 × 10?20 cm2) at around 405 nm, indicating that it can be pumped efficiently by the commercialized GaN/InGaN laser diode. Three Judd-Ofelt intensity parameters Ωt (t = 2, 4, 6) were calculated to be 5.177, 3.783 and 2.218 × 10?20 cm2, respectively. The stimulated emission cross section at 614 nm was calculated to be 0.471 × 10?20 cm2 and the fluorescence lifetime for 4G5/2 level was fitted to be 1.90 ms. All these results suggest that Sm:GLSO is very promising for realizing reddish-orange laser operation using the current commercialized GaN/InGaN laser diode pumping.
关键词： Czochralski method,Mixed laser crystal,Judd-ofelt,Sm:GLSO,Reddish-orange laser
更新于2025-09-12 10:27:22
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Thermal analysis and 1.38?μm CW laser performances based on a new tungstate crystal Nd3+:Na2La4(WO4)7
摘要： 1.38 μm diode-end-pumped crystalline lasers have important applications and studies are worthy to be conducted since it is not easy to realize the 1.38 μm laser emission in Nd3+-doped crystals. In this paper, a Nd3+:Na2La4(WO4)7 crystal with dimensions of f 21×37 mm3 was successfully grown by the Czochralski method. The distributions of heat on the end-pump facet and along the axial orientations were analyzed and its effect on the laser properties at 1.38 μm was considered. Then, based on the physical properties of the Nd3+:Na2La4(WO4)7 crystal and the results of the thermal effects analysis, we designed the oscillation cavity and finally a 1381 nm laser was demonstrated with the maximum output power of 1.87 W. The slope efficiency is 22.8%. Results show that the Nd3+:Na2La4(WO4)7 crystal will be advantageous for the applications of ~1.38 μm laser in many areas.
关键词： Nd3+:Na2La4(WO4)7,thermal analysis,Czochralski method,1.38 μm laser,diode-end-pumped
更新于2025-09-11 14:15:04
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Scintillation properties and increased vacancy formation in cerium and calcium co-doped yttrium aluminum garnet
摘要： Co-doping with divalent elements is known to improve the light yield and decay times of some cerium-activated scintillators, despite the stabilization of tetravalent Ce4+, previously believed to be non-luminescent, from the Ce3+ state. Ce4+ stabilization is a charge compensation mechanism which results from divalent ion substitution of a 3 + site. To elucidate the underlying mechanisms, which remain poorly understood, we have grown three Ce,Ca:YAG crystals with di?erent amounts of calcium co-dopants by the Czochralski method and characterized their scintillation and defect properties. Calcium co-doping reduces the decay times and stabilizes the formation of Ce4+ as expected. Interestingly, X-ray ?uorescence analysis reveals a decreased concentration of cerium within the YAG crystal for the sample doped with high levels of Ca, which could contribute to the observation that scintillator properties are improved only for low levels of Ca co-doping. Additionally, positron annihilation spectroscopy reveals an increase in the concentration of vacancies with increasing Ca concentration, while thermoluminescence is observed to show no detectable signal. Furthermore, room temperature photo-luminescence of the Ce 4f to 5d1 transition demonstrates decreased emission with increasing Ca co-doping. These data suggest that Ca co-doping decreases the decay time by creating defects with non-radiative decay pathways.
关键词： A2. Czochralski method,B2. Scintillator materials,A2. Single crystal growth,A1. Defects,B3. Scintillators,A1. Doping
更新于2025-09-11 14:15:04
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In-situ measurement of CO gas concentration in a Czochralski furnace of silicon crystals
摘要： Power devices with high-performance require long carrier lifetimes within their silicon crystals. This paper reports the in-situ measurement of carbon monoxide in a Czochralski growth furnace of silicon single crystals. Moreover, this paper reports analytical investigation on contamination to silicon melt as functions of pressure in the furnace, argon gas ?ow velocity and gap width between the melt and a thermal shield. The experimental results show the carbon contamination to the melt increases when the pressure increases and the ?ow rate decreases. Increase of the gap width increases the contamination of carbon. We could explain the results qualitatively using a simple transport model.
关键词： A1. Mass transfer,A1. Impurities,A2. Czochralski method
更新于2025-09-04 15:30:14