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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.

The purpose of this work was to systematically assess the distribution of thermoluminescence (TL) and optically stimulated luminescence (OSL) properties along the length of crystals grown by the micro-pulling-down method, in relation to the microstructure and distribution of activators. We analyzed lithium magnesium phosphate (LiMgPO4, LMP) crystals doped with terbium (Tb, 0.8 mol%) or with a combination of thulium (Tm, 0.8 mol% or 1.2 mol%) and boron (B, 10 mol%). Crystals of several centimeters in length and 3 mm in diameter were cut into 20&ndash, 40 slices, depending on length. For each sample, TL glow curves and OSL decay curves were examined. Optical microscopy and scanning electron microscopy were used to assess the microstructure and elemental composition of several selected samples. Two-dimensional TL readouts were performed to identify the areas with higher and lower signal emission. Our study showed that there may be significant differences not only in LMP sensitivity along the crystal&rsquo, s axis but also on the surface of the slice. The distribution of activators varies depending on the type of crystals and strongly affects luminescence properties.

International audience; Tm3+-doped bismuth germanate crystals (Tm:BGO) with various doping concentrations of 0.5, 0.75, 1.0, 1.5, and 2.0 at.% were grown by the micro-pulling-down method (μ-PD). The effect of thulium concentration on the growth, structure, absorption spectra, emission spectra and fluorescence lifetime of 3H4 and 3F4 state was studied. Under excitation of 792 nm, Tm:BGO crystals exhibit two fluorescence bands corresponding to the 3H4 → 3F4 and the 3F4 → 3H6 transitions. The fluorescence lifetime of 3H4 state decreased strongly as the thulium concentration increased, while the lifetime of 3F4 state was relatively constant for all thulium concentrations

Single crystals fiber (SCF) of LuAG doped with 2.0 at.% thulium has been grown by using micro-pulling down (µ-PD) technique. A continuous-wave output power of 2.44 W was achieved with a slope efficiency of 11.7% using a 783-nm diode laser as pump source. The beam quality factors M2 were 1.14 and 1.67 in the x and y directions, respectively. This is, to the best of our knowledge, the first report on the Tm:LuAG SCF laser. Using ray tracing analysis, the influence of laser performance by the pump intensity distribution in the SCF was also studied.

SrB4O7 (SBO) has recently received much attention as a wavelength-conversion material which can operate into the deepest ultraviolet wavelengths (125 nm). The utilization of SBO for semiconductor lithography and laser ablation requires fully transparent crystals. Here, we show the growth of SBO crystal fibers with near-stoichiometric composition by the μ-pulling-down method. SrB2xO3x+1 ceramics sintered with various values of x were evaluated by X-ray diffraction (XRD). The melting point of the SBO ceramics was measured by differential scanning calorimetry (DSC) as 1017 °C, and the heat of fusion was 63.3 J/g. Furthermore, we observed SBO crystal fibers grown with various x values by optical microscopy. As a result, even when the deviation from stoichiometric composition was ± −0.1 mol % SrO (x = 2 ± 0.004), SrB2O4/SrB6O10 appeared. Also, DSC curves of SBO ceramics exhibited only one melting peak. These results demonstrate that SBO shows no solid-solution width and that the stoichiometric composition is e...

The MgO-MgAl2O4 eutectic was directionally solidified via micro-pulling down method in the form of rods with 2–3 mm diameter. MgAl2O4 single crystals (with orientation) were used as crystallization seeds. At low pulling rates, especially 0.15 mm/min triangle-like cross-section was observed, which was linked to the eutectic MgAl2O4 following the crystallographic direction of the seed. MgO precipitates in the form of lamellae and rods with median equivalent diameter ranging from 0.19 to 0.85 μm, depending on the pulling rate. The preferred crystallization direction was for both phases, however notable traces of other directions, e.g. , and were found as well.

Tm3+-doped calcium niobium gallium garnet (Tm:CNGG) single crystals have been successfully grown by the micro-pulling-down (μ-PD) method. The crystal structure, absorption spectra, fluorescence spectra and lifetimes of Tm:CNGG crystals were investigated. The absorption and emission bandwidths of Tm:CNGG crystals are larger than those of other Tm3+ doped garnet crystals, which will be beneficial for laser diode (LD) pumping and ultrashort pulse generation. Additionally, continuous wave (CW) laser operation around 2 μm was achieved in the 2.0 at.% Tm:CNGG crystal by LD pumping.

Cu-doped sodium potassium niobate single crystal fibers (KNN-Cu) were grown by the micro-pulling-down technique under different atmospheres, namely, argon, synthetic air and oxygen. The str...

Eu3+-doped Bi4Ge3O12 (BGO) single crystal with the size of O2 × 83 mm3 was successfully grown by the micro-pulling-down method. The absorption cross section, emission cross section and Judd–Ofelt analysis of Eu:Bi4Ge3O12 (Eu:BGO) were reported for the first time. The absorption cross-section is 1.03 × 10−20 cm2 with full-width at half-maximum of 3.1 nm at around 393 nm. The spectroscopic intensity parameter Ωt (t = 2,4,6), radiative transition probabilities, branching ratios and radiative lifetime were obtained, respectively. Furthermore, the stimulated emission cross-section centered at 611 nm was calculated to be 6.32 × 10−21 cm2. The fluorescence lifetime of 5D0 level was obtained to be 1.51 ms. The results indicate that Eu: BGO single crystal could be a potential laser host in the visible range.

Within this work, the undoped and Ce3+ doped Y2O3 – Al2O3 double system crystals were grown from the melt by micro-pulling-down method and their basic luminescent properties have been investigated. Luminescent properties of the obtained crystal samples were studied by cathodo- and thermo-luminescence methods (CL and TL, respectively). The TL spectra were measured after the samples irradiation with both beta and alpha particles. It was found that the obtained cerium doped crystals exhibit dominant emission bands with maxima at around 380 nm in the centers of crystals, and low-intensive satellite band peaked at 560 nm at the boundaries of crystals, what corresponds to the well-known perovskite and garnet phases, respectively. For Y Lu substituted crystals only the emission band of garnet phase was observed. It tends to suggest that even a small substitution of Y3+ by Lu3+ ions in the host lattice causes a strong suppression of the 380 nm luminescence of the perovskite phase. This was also confirmed by TL spectra measurements performed over the different spectral ranges. A good agreement of CL and TL emission spectra suggests that the same emission centers are involved in both processes. The obtained results showed that, besides of the well-known scintillating properties, the materials under study can be also considered as the energy storage phosphors for dosimetric applications.

International audience; BaTiO3-based crystal fibres with mm-sized grains were grown by the micro-pulling down technique from the BaTiO3–CaTiO3–BaZrO3 solid solution with pulling velocities of about 6, 9 and 15 mm h−1. The natural growth direction was identified as (001)pc. For the pulling velocities of about 15 mm h−1 and 9 mm h−1, effective partition coefficients have been calculated from Castaing micro-probe measurements, and gave, respectively, 1.3 and 2 for Zr, and 0.95 and 0.9 for Ca. Laser-induced breakdown spectroscopy measurements reveal a strong inhomogeneity and variations of Zr contents while Ca contents show an opposite variation trend with a more steady distribution. Coexistence of two crystallized perovskite solid solutions is suggested. Most efficient polycrystals with mm-sized grains and 0.5 mol% Zr and 11 mol% Ca as average contents exhibit Curie temperatures higher than 113 °C, electromechanical coupling factors kt up to 41% and piezoelectric charge coefficients d33 up to 242 pC N−1 at room temperature. These values are similar to piezoelectric coefficients reported in the literature for oriented flux-grown single crystals with close compositions. Both chemical and physical results obtained in the BCTZ system make the μ-PD technique a promising way to improve the piezoelectric response of lead-free solid solution-based single crystals.

Single-crystal fiber (SCF) combines the advantages of bulk crystal and glass fiber gain media and shows broad application prospects in all-solid-state lasers. In this work, high-quality crack-free Nd:YAG SCFs with diameters of 0.8–1 mm were successfully grown by the micro-pulling-down (μ-PD) method. The as-grown SCFs showed homogeneous Nd3+ distribution, with a diameter fluctuation of less than 5%. The X-ray Laue patterns on the different crystal positions also revealed good crystalline consistency. Moreover, the core stress problems were investigated in terms of growth orientation to improve the crystal quality, and seed crystals with orientation of , and to 15° were used for crystal growth. Continuous-wave laser operations at 1064 nm were realized with the as-grown Nd:YAG SCFs. The maximum output of 8.32 W with a laser beam quality factor M2 = 1.08 was achieved.

International audience; A series of Ce-doped YAG-Al2O3 eutectics were grown by the micro-pulling-down (μ-PD) method, for the purpose of high power white light emitting diodes. The eutectic structure was investigated. A calibrated integrating sphere spectrometer setup was used to measure the white LED properties of eutectic samples. The CIE color coordinates can be regulated easily by altering the Ce3+ doping concentration and sample thickness of the Ce:YAG-Al2O3 eutectics. A 1 W white LED device based on Ce:YAG-Al2O3 eutectics at a rated current of 350 mA emitted a bright white light with a CIE coordinate of (0.319, 0.334), a luminous efficacy of 83.0 lm W−1 and a Duv value of 0.003. The results showed that Ce:YAG-Al2O3 eutectics have better luminescence properties than commercial powder phosphors at a high current density.

International audience; A technological advance in shaped μ-PD crystal growth provided us with high-quality single crystalline fibres of rare-earth garnets with the good longitudinal transparency and light attenuation length of up to 1 m.New high-energy experiments in colliders have increased the demand for cheap and radiation-hard detector materials that can be mass produced. The concepts of a new generation of high-energy physics experiments include combined electromagnetic and hadron calorimeters for the simultaneous detection of scintillation and Cherenkov emission using undoped and lanthanide-doped crystalline fibres. The micro-pulling-down (μ-PD) method provides the growth of long single crystalline fibres in a ready-to-use shape without the need for further cutting and polishing. In this highlights paper, recent achievements relating to the μ-PD growth of long Y3Al5O12 (YAG)- and Lu3Al5O12 (LuAG)-based fibres from the Institute of Light and Matter are reviewed. Optimization of the Ce concentration, pulling rate, and crystallizer configuration resulted in the formation of highly transparent LuAG:Ce fibres with a light attenuation length of up to 1 m. Meanwhile, such excellent transparency has not been reproduced in YAG:Ce fibers. The main differences in the crystallization processes of YAG- and LuAG-based fibres are discussed in connection with their physical properties. The paper also addresses the codoping of garnet fibres with Mg2+ ions and growth from non-stoichiometric melts to adjust fiber transmission and scintillation performance.

Directional solidification experiments have been carried out in eutectic and off eutectic composition in Al2O3–YAG–ZrO2 system using the micro-pulling down (μ-PD) technique. The formation of different microstructures of stable phases, over a range of velocities studied, is discussed. During the solidification process, coupled growth microsctrucure can occur at off eutectic composition. Colonies and dendrites were analysed as a function of the composition and velocity. Increasing the solidification rate resulted in a smaller grain size and instability of the crystallization interface with respect to ZrO2 segregation at the solidification front. Increasing ZrO2 in the eutectic composition showed enhanced tendency for colony and dendrite formation. When the velocity was extended to the rapid solidification regime (>1.75 mm min−1), the geometrical pattern microstructure was found to grow and a change in the growth orientation of Al2O3 corresponding to c-axis (0 0 01) was observed. Whatever the pulling rate, during the eutectic solidification the Al2O3 and ZrO2:Y phases' growth competition was observed, and 〈100〉 YAG orientation was grown along the pulling direction.

Single-crystal fibers (SCFs) have a great application potential in high-power lasers due to their excellent performance. In this work, high-quality and crack-free Yb3+:Lu3Al5O12 (Yb:LuAG) SCFs were successfully fabricated by the micro-pulling-down (&mu, PD) technology. Based on the laser micrometer and the X-ray Laue diffraction results, these Yb:LuAG SCFs have a less than 5% diameter fluctuation and good crystallinity along the axial direction. More importantly, the distribution of Yb ions is proved to be uniform by electron probe microanalysis (EPMA) and the scanning electron microscope (SEM). In the laser experiment, the continuous-wave (CW) output power using a 1 mm diameter Yb:LuAG single-crystal fiber is determined to be 1.96 W, at the central wavelength of 1047 nm, corresponding to a slope efficiency of 13.55%. Meanwhile, by applying a 3 mm diameter Yb:LuAG SCF, we obtain a 4.7 W CW laser output at 1049 nm with the slope efficiency of 22.17%. The beam quality factor M2 is less than 1.1 in both conditions, indicating a good optical quality of the grown fiber. Our results show that the Yb:LuAG SCF is a potential solid-state laser gain medium for 1 &mu, m high-power lasers.

International audience; Al2O3-YAG-ZrO2 eutectic ceramic rods of 5 mm in diameter were grown by micro-pulling down technique. The seeding and the solidification rate affect microstructure, morphology, crystallography, and thermal stress of the solidified ceramics. The ternary eutectic grown through zirconia (111) seed had inhomogeneous and irregular cellular microstructures. At the stationary stable regime, the microstructure spacing (λ) depends on the pulling rate (v). Under solidification rate of 0.5 mm.min−1, the rods grown by using eutectic poly-crystal, (100), (111) YAG, and c(0001), A(1−210), M(10−10) sapphire seeds, the YAG and ZrO2 phases are oriented along the direction parallel to the growth direction. The zirconia (111) seeding X-ray diagram eutectic presents additional peaks and the monoclinic ZrO2 phase appears at the solidification rate of 1 mm.min-1. The rods grown through ZrO2 seeding are more stressed than those solidified by using eutectic, YAG and sapphire seeds, respectively.

International audience; Tm3+ doped and Tm3+, Pr3+ co-doped Lu3Al5O12 (LuAG) garnet single crystals have been successfully grown by the micro-pulling-down (μ-PD) method. The absorption spectra, fluorescence spectra and lifetimes were investigated at room temperature. In the absorption spectra, the transition centered at 782 nm matches well with the GaAlAs LDs laser pumping. The incorporation of Pr3+ into Tm3+-doped LuAG crystals enhanced the intensity of 1.5 μm emission and decreased the fluorescence lifetime of the lower energy level for 1.5 μm emission from 10.427 ms to 2.603 ms. The results indicate that Tm,Pr:LuAG crystal can be promising candidate for near infrared 1.5 μm laser materials.

International audience; Highly textured cm-sized (Ba1−xCax)TiO3 (x = 0.05) polycrystals at off-eutectic composition were grown by the micro-pulling down freezing technique from a BaTiO3–CaTiO3 system at a high pulling velocity of about 48 mm h−1. Textured polycrystals exhibiting submillimetre-sized dendrites along the (110)pc growth direction and geometrical grains along the (100)pc direction were revealed by a complementary analysis performed by Laue diffraction and EBSD techniques. An average Ca content of about x = 0.0435 was measured throughout the whole volume of the boule and led to an effective partition coefficient of Ca of about 0.87. LIBS measurements highlighted the local segregation of Ca and major impurity contents within dendrites, grains and at the grain boundaries. Dielectric and piezoelectric measurements performed on oriented polycrystalline textured samples led to Curie temperatures up to 116 °C and d33 up to 214 pC N−1, in very good agreement with literature values. Both chemical and physical results obtained in the BCT system make the μ-PD technique a promising and alternative way to improve the piezoelectric response of lead-free solid solution-based crystals through their texturing along preferential crystallographic directions.

International audience; Spectroscopic and luminescent properties of europium (Eu), erbium (Er), thulium (Tm) doped LiGd(WO4)2 fibers crystals, present high performances for investigation in phosphorus and laser applications. We have successfully grown 2 at % Eu, Er and Tm-doped LiGd(WO4)2 singles-crystals fibers by the Micro Pulling Down (μ-PD) technique (melting point above 1115 °C) using a pulling rate in the range of 0.08–0.15 mm/min. The crystallization interface was flat, with meniscus length equal to the fiber radii. The absorption and emission spectra were measured at room temperature. The absorption and emission cross sections of the Eu3+, Er3+, and Tm3+ transitions were evaluated. For the erbium cation we register 4S3/2 → 4I15/2, 2H11/2 → 4I15/2 transitions in the visible and 4I13/2 → 4I15/2 in IR range. The emission spectra recorded in the visible and infrared range with fluorescence correspond to 1G4→3F4 +3F2, 3F3→ 3H6, 3H4 → 3H6, and 1G4 → 3H5 for the thulium, instead for the europium we have 5D1→7F1,2 and 5D0 → 7F0-1-2-3-4, transitions. This last one presents an excellent structural probe for investigating the local environment of Eu3+ dopant in LiGd(WO4)2 host. The fluorescence lifetimes associated to these intense transitions were investigated. The polarized IR and Raman spectra of LiGd (WO4)2 single crystal fiber were measured, parallel and perpendicular to the fibers growth direction. We observed a bonds at 915 cm-1 for IR and 913 cm-1 for Raman corresponding of the symmetric stretching mode of the isolated tetrahedra (WO4)-2 group.

The scintillation and energy-storage properties of YAlO3 (YAP) crystals doped with Sc3+ and La3+ isoelectronic dopants were investigated in this work. The YAP:Sc and YAP:La crystals were grown from the melt with a nominal Sc and La content in the 0.2&ndash, 5.0 mol.% range using the novel micro-pulling-down method. We found that the segregation coefficient of Sc ions in YAP:Sc (0.2&ndash, 1.0 mol.%) crystals is about of 0.35&ndash, 0.4 and decreases to around 0.2 at Sc content of 5.0 mol.% when the segregation coefficient of La ions in YAP:La (1.0&ndash, 5.0 mol.%) crystals is 0.008&ndash, 0.01. The scintillation and stimulated luminescence phenomena, like thermo- and photoluminescence, were utilized for the property characterization of the studied materials. The cathodoluminescence and X-ray-excited luminescence were used for the imitation of scintillation in the YAP:Sc and YAP:La crystals. The influence of Sc3+ and La3+ dopant concentration on the CL and RL emission spectra, as well as the shape of the measured thermoluminescence (TL) glow-curves, was also investigated. The measured emission spectra showed dominant emission of Sc3+ and La3+ ions in the UV range. For this reason, the YAP:Sc and YAP:La crystals can be considered for creation of ultraviolet (UV)-emitting scintillators. For the undoped YAlO3 crystals, the main TL emission peak occurs in a low-temperature range at 375 K. Meanwhile, even a small addition of dopants causes a strong suppression of luminescence of the YAP host and high-temperature peaks become dominant in the TL glow-curves of YAP:Sc and YAP:La crystals. Moreover, the amplitude of emission does not change monotonically with increasing dopant content. The kinetic parameters of emission were also evaluated, and the first-order behavior was confirmed in all cases. The dosimetric properties of investigated materials such as dose response, fading rate, and the lowest measurable dose are also discussed. The obtained results tend to suggest that the YAlO3 perovskite host, apart from its application for the development of efficient scintillators, may also be considered as a promising matrix for the creation of energy-storage phosphors for dosimetric applications.

International audience; Nd3+ doped Y3ScxAl5-xO12 (x = 0.05, 0.5, 1) single crystals were successfully grown by the micro-pulling-down (μ-PD) technique. The effect of compositional parameter x on the structure, absorption, emission and fluorescence lifetime of Nd:Y3ScxAl5-xO12 crystals was studied. The Nd3+ concentration in the core increased with increasing of compositional parameter x. The full width at half maximum (FWHM) of the emission band centered at 1064 nm was calculated to be 6.1, 7.1, and 7.3 nm for x = 0.05, 0.5 and 1, respectively. The fluorescence lifetimes of 4F3/2 levels are 259.3, 269.6, and 276.9 μs for x = 0.05, 0.5, and 1, respectively. The results indicate that the Nd:Y3ScxAl5-xO12 crystals are promising materials for laser output.

International audience; We report on the comparative growth and spectroscopy of Eu3+-doped Y3Al5O12 (YAG) and Y3ScAl4O12 crystals grown by the micro-pulling-down (μ-PD) method. The structure of the as-grown crystals was determined by X-ray diffraction (XRD) and Raman spectroscopy. The absorption spectra of the crystals are dominated by a strong line centered at 395 nm, matching well with the emission of commercial ultraviolet laser diodes. The Eu:YAG and Eu:Y3ScAl4O12 crystals exhibit strongest red emission centered at 710 nm and the full width at half maximum (FWHM) was calculated to be 2.03 and 3.19 nm, respectively. The fluorescence decay curves of 5D0 levels were measured and discussed. All the results indicate that the Eu:YAG and Eu:Y3ScAl4O12 crystals are promising candidates for red luminescent/laser materials.

This paper is the first part of a 2D description of a single crystal thin plate growth by micro-pulling–down (μ-PD) method. This part concerns the following aspects: the free surface equation and the pressure difference across the free surface (section 2); limits of the pressure difference p across the free surface (section 3); static stability of the free surface (section 4); the plate half thickness change rate due to the change of the pressure difference p across the free surface and the half half-thickness control (section 5). Numerical illustrations of the above aspects is given in case of a Si thin plate of 0.0001 [m] by using the Maple 17 software. The advantage of this description is that it helps to better understand the dependence of the meniscus free surface shape and size on the pressure difference across the meniscus free surface and may help the automation of manufacturing.

This paper is the second part of a 2D description of a single crystal thin plate growth by micro-pulling–down (μ-PD) method. This part concerns the following aspects: temperature distribution and melt flow in the melt–crystal system (section 2); impurity distribution (section 3). Numerical illustration concerning the above aspects are given for the growth of a thin Si plate of 0.0001 [m] by using COMSOL Multiphysics software. The advantage of this description is that it helps in the better understanding of the impurity dispersion in meniscus and may help the improvement of crystal quality.

Pulling growth technique serves as a popular method to grow congruent melting single crystals with multiscale sizes ranging from micrometers to centimeters. In order to obtain high quality single crystals, the crystal constituents would be arranged at the lattice sites by precisely controlling the crystal growth process. Growing interface is the position where the phase transition of crystal constituents occurs during pulling growth process. The precise control of energy at the growing interface becomes a key technique in pulling growth. In this work, we review some recent advances of pulling technique towards rare earth single crystal growth. In Czochralski pulling growth, the optimized growth parameters were designed for rare earth ions doped Y3Al5O12 and Ce:(Lu1− x Y x )2SiO5 on the basis of anisotropic chemical bonding and isotropic mass transfer calculations at the growing interface. The fast growth of high quality rare earth single crystals is realized by controlling crystallization thermodynamics and kinetics in different size zones. On the other hand, the micro pulling down technique can be used for high throughput screening novel rare earth optical crystals. The growth interface control is realized by improving the crucible bottom and temperature field, which favors the growth of rare earth crystal fibers. The rare earth laser crystal fiber can serve as another kind of laser gain medium between conventional bulk single crystal and glass fiber. The future work on pulling technique might focus on the mass production of rare earth single crystals with extreme size and with the size near that of devices.

Submicrometer diameter phase-separated scintillator fibers (PSSFs) were reported and they possessed both the properties of an optical fiber and radiation-to-light conversion. The PSSFs were fabricated using a directionally solidified eutectic system. High-resolution X-ray imaging can be developed using the PSSFs. In this paper, Tb- and Eu-doped GdAlO3 (GAP)/ $\alpha $ -Al2O3 eutectic scintillator was grown by the micro pulling down method with various growth rates in order to achieve the high light output and the high light-guiding efficiency. Relationship between radioluminescence intensity and dopant concentration of Eu and Tb was investigated. At the optimized dopant concentration, relationship between growth rate, eutectic period structure, diameter of PSSFs, and contrast transfer function was investigated to achieve high-resolution X-ray imaging.

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.

Premature melt solidification is the solidification of a melt during mold filling. In this study, a numerical model is used to analyze the influence of the pouring process on the premature solidification. The numerical model considers three phases, namely, air, melt, and equiaxed crystals. The crystals are assumed to have originated from the heterogeneous nucleation in the undercooled melt resulting from the first contact of the melt with the cold mold during pouring. The transport of the crystals by the melt flow, in accordance with the socalled “big bang” theory, is considered. The crystals are assumed globular in morphology and capable of growing according to the local constitutional undercooling. These crystals can also be remelted by mixing with the superheated melt. As the modeling results, the evolutionary trends of the number density of the crystals and the volume fraction of the solid crystals in the melt during pouring are presented. The calculated number density of the crystals and the volume fraction of the solid crystals in the melt at the end of pouring are used as the initial conditions for the subsequent solidification simulation of the evolution of the as-cast structure. A five-phase volume-average model for mixed columnar-equiaxed solidification is used for the solidification simulation. An improved agreement between the simulation and experimental results is achieved by considering the effect of premature melt solidification during mold filling. Finally, the influences of pouring parameters, namely, pouring temperature, initial mold temperature, and pouring rate, on the premature melt solidification are discussed.

During crystal growth in heat exchanger method (HEM) system, the shape of the growth interface changes with the proceeding of the growth process, which limits the crystal size and reduces the quality of the crystal. In this paper, a modified HEM system is proposed to control the interface shape for growth of sesquioxide crystals. Numerical simulation is performed to predict heat transfer, melt flow and interface shape during growth of high melting sesquioxide crystals by the heat exchanger method. The results show that a flat or slightly convex interface shape is beneficial to reduce the solute pileup in front of the melt/crystal interface and decrease the radial temperature gradient inside the crystal during growth of sesquioxide crystals. The interface shape can be controlled by adjusting the gap size d and lower resistance heater power during growth. The growth rate and the melt/crystal interface position can be obtained by two measured temperatures.

Ce-doped YAG/Al2O3 melt-growth composite (MGC) samples were grown by the micro-pulling-down (μ-PD) method, and their physical and chemical properties were investigated. The grown MGC samples exhibit fine-grained granophyric texture at the micron scale. Fluorescence spectra, excited by a blue laser diode, were recorded, and, in particular, the finely textured granophyric MGC sample doped with 0.1 at% Ce and prepared with a growth rate of 3 mm/min shows superior fluorescence properties without high-temperature deterioration of fluorescence intensity. The μ-PD method is demonstrated to be applicable for manufacturing finely textured MGC samples with improved luminous efficiency as phosphors for white LEDs.

Eu3+-Doped CaMoO4 single-crystal fibers with concentrations from 0.01 to 1 at% have been grown by the micro-pulling-down method in an air atmosphere. The origin of the coloration of the crystals can be attributed to the charge compensations. In the air or H2 annealing process, the absorption spectra combined with XPS proved the coexistence of Eu2+ and interstitial O (Oi2-). The density functional theory was simulated to display the absorption spectra of Eu2+-doped and (Eu2+-Oi2-) co-doped CaMoO4, consistent with the experimental data. The low-temperature polarized absorption and emission spectra illustrated the charge compensations. The luminescence spectra of the Eu3+ probe were used to study the Oi2- species. Luminescence decay curves of 5D0 were measured. To the best of our knowledge, this is the first report on the growth and charge compensations of Eu3+:CaMoO4 single-crystal fibers grown by the micro-pulling-down method and the reduction phenomenon of Eu3+ to Eu2+ in an oxidizing atmosphere at high temperature in molybdates. On excitation by near ultraviolet or blue light, the molybdates could be potential hosts for white-light-emitting diodes.

Cross-sectional shape-controlled Fe-Ga alloy crystals for energy harvester applications were grown using the micro pulling down (μ-PD) method. The investigation of material concentrations along the growth direction reveals that a high growth rate of 5.0 mm/min raises the effective segregation coefficient of Ga, k eff (Ga), and ensures high concentration homogeneity. However, the high growth rate was speculated as causing non-preferentially oriented portion formation that decreases the magnetostrictive property. The magnetostriction 3/2λ = 286 ppm was achieved for a good oriented sample (i.e. the misorientations from 〈100〉 were less than 7.5°.) with the Ga concentration of 16.8 at%. A prototype vibration energy harvester using a plate-shaped Fe-Ga alloy grown at 5.0 mm/min showed comparable or superior performance to the device using commercially available alloys. By leveraging the advantages of near net-shape controlling and a higher growth rate than other crystal growth techniques, the μ-PD method is expected to emerge as a new technique for mass-producing Fe-Ga alloys as materials for energy harvester applications.

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.

Luminescence, scintillation and photoconversion properties of Gd3Al5−x−yScxGayO12:Ce crystals, grown by the micro-pulling-down method, were studied upon substitution of Al for Sc3+ and Ga3+ in the x = 1–2;y = 1–3 ranges. A decrease of the band gap and crystal field strength occurs in these garnets with increasing Sc3+ and Ga3+ content, resulted in blue-shift and reduced thermal stability of Ce3+ emission. Lowering of the scintillation light yield of crystals by two times and scintillation decay kinetic acceleration from 97 to 27 ns is observed at increasing Ga content in the y = 1–3 range. Sc and Ga admixing increases the number of deep charge traps, which additionally deteriorate of crystals scintillation performance. Application of Gd3Al5−x−yScxGayO12:Ce crystals as phosphor converters of white LED was considered. Increasing the Sc3+ and Ga3+ content in crystals leads to linear blue shift of the converter emission and results in increasing the color temperature of LEDs from neutral to could white light.