Laser Heated Pedestal Growth Research Articles

The Growth and Properties of Y Admixed Luag:Ce Scintillating Single Crystal Fiber Fabricated by Laser Heated Pedestal Growth Method

The Growth and Properties of Y Admixed Luag:Ce Scintillating Single Crystal Fiber Fabricated by Laser Heated Pedestal Growth Method

Anisotropic bubble defects and stress distribution in LuAG single-crystal fibers grown by the laser-heated pedestal growth method

The effects of orientation and growth chamber pressure on bubbles and stress distribution of LuAG SCFs grown by the LHPG method were studied.

Sensitive Ho3+,Yb3+ co-doped mixed sesquioxide single crystal fibers thermometry based on upconversion luminescence

Mixed sesquioxide crystals (R2O3, R = Lu, Y or Sc, where R is occupied by two different elements) have drawn an increasing attention due to their outstanding physical and chemical properties. In this work, we have grown Ho3+,Yb3+ co-doped mixed sesquioxide LuYO3 and LuScO3 single crystal fibers (SCFs) in centimeter-length by laser heated pedestal growth (LHPG) method for optical temperature sensing. Both mixed sesquioxide SCFs yield strong green emission (5F4,5S2→5I8) and weak red emission (5F5→5I8) under the excitation of 980 nm laser. Their upconversion (UC) levels are not thermally coupled levels (NTCL). Importantly, these mixed sesquioxide SCFs show a good temperature sensitivity in the temperature range of 298–748 K. Using UC fluorescence intensity ratio (FIR) method, the calculated maximum values of absolute sensitivity of Ho,Yb:LuYO3 and Ho,Yb:LuScO3 are 0.1603 (at 303 K) and 0.0886 K−1 (at 300 K), respectively. These features indicate that our grown mixed sesquioxides show a great potential for high-sensitivity temperature sensing applications. Furthermore, the presented mixed sesquioxide SCFs are excellent candidates for the high-integrated temperature sensor.

Growth and Characterization of Ce-Doped Luag Single Crystal Fibers from Transparent Ceramics by Laser-Heated Pedestal Method

Scintillation single crystal fibers (SCFs) have great potential applications in the new generation of high-energy ray and particle detectors due to their morphological advantages. In this work; Ce:LuAG SCFs with a diameter of 1 mm were grown along the direction of [111] by laser-heated pedestal growth (LHPG) method using a transparent ceramic as the source rod; and a doping concentration was 0.1 at%, 0.3 at%, 1 at%, respectively. The effects of growth rate and annealing in air on the scintillation and optical properties of SCF are discussed in detail. The results of analyzing the absorption spectra; radioluminescence (RL) spectra; pulse-height spectra and fluorescence lifetime of SCFs show that the SCF maintains excellent scintillation performance while having a fiber structure. Therefore; Ce:LuAG SCF is a potential candidate material for detector.

Determination of sapphire crystal melt refractive index in visible range

The refractive index (RI) of a sapphire crystal melt was determined at high temperatures (exceeding 2350 K) in the visible spectral range. Data were obtained from the analysis results of the state of polarization of the intrinsic thermal radiation of the melt during the laser-heated pedestal growth process. The derived sapphire melt RI is n = 1.72 ± 0.02 for λ = 550 nm, and the linear part of the dispersion in the range 400–750 nm is characterized by the coefficient dn/dλ = −(1.93 ± 0.01) × 10–4 nm − 1.

Compact Q-switched Nd:YAG single-crystal fiber laser with 794 nm laser diode pumping

A promising Nd:YAG single-crystal fiber (SCF) was successfully fabricated by the laser-heated pedestal growth method. The compact passively Q-switched laser has been realized for the first time with a 794 nm laser diode pumping. Pulsed laser performances of this SCF were investigated in detail with a flat-flat resonator. Under the absorbed pump power of 2.50 W, the peak power of 274.24 W was obtained with 19.41 ns pulse duration width and 65.94 kHz repetition rate.

Optical temperature sensing characteristics of Sm3+ doped YAG single crystal fiber based on luminescence emission

A series of YAG: x mol%Sm3+ single crystal (SC) materials, in which x is 0.3, 0.5, 1, 2, respectively, have been synthesized through laser heated pedestal growth (LHPG) method. The down-conversion luminescence properties of prepared fluorescent materials were investigated under a 405 nm laser. According to the results, 0.5 mol% was selected as the optimal doping concentration, and the integrated YAG single crystal fiber (SCF) with end Sm3+ doped was further fabricated. Then the optical temperature sensing characteristics were studied by the technique of the fluorescence intensity ratio (FIR) in detail. It shows that 4F3/2 and 4G5/2 of Sm3+ ions are thermally coupled energy levels. The FIR of the 4F3/2/4G5/2 → 6H5/2 increases monotonously as temperature rises, and its temperature measurement range can be extended to 1178 K. The maximum absolute sensitivity and maximum relative sensitivity are 3.046 × 10−4 K−1(1129 K) and 5.033 × 10−3 K−1 (500 K), respectively. Additionally, the FIRs of various emission bands from 4G5/2 → 6H5/2, 7/2 and the FIR of the emission sub-bands from 4G5/2 → 6H9/2 exhibit temperature dependence in 303–1028 K and 303–878 K, respectively. These results indicate that YAG: Sm3+ SC is a very promising high-temperature sensing material.

Exploring promising up-conversion luminescence single crystal fiber in sesquioxide family for high temperature optical thermometry application

Facing the needs of optical thermometry application, the 0.5 at% Tm3+, 5 at% Yb3+ co-doped sesquioxide family (Lu2O3, LuScO3 and Sc2O3) single crystal fibers (SCFs) were successfully grown by the laser heated pedestal growth (LHPG) method. The Tm3+ and Yb3+ ions are uniformly distributed in the three fibers. The power dependent emission spectra with 980 nm excitation from 20 to 220 mW were investigated. There is a good linear relationship between the logarithm of emission intensity and the pumping power. In addition, the up-conversion luminescence (UCL) of the transitions of 3F2,3 →3H6 from 670 to 730 nm and 3H4 →3H6 from 750 to 850 nm of Tm3+ were systemically obtained with different temperature under a 980 nm laser. The maximum values of relative sensitivity of the Lu2O3, LuScO3 and Sc2O3 crystal fibers are 0.0056, 0.0180, 0.0067 K−1, corresponding to the temperature of 535, 323 and 427 K, respectively. The highest detection temperature of Lu2O3 and LuScO3 crystals was 973 K, while that of Sc2O3 crystal was up to 1073 K. Considering that Tm3+, Yb3+: Sc2O3 crystal still had high emission intensity at 1073 K, and the absolute sensitivity increases with increasing temperature, it was believed that the Sc2O3 crystal fiber was particularly suitable for higher temperature and sensitivity detection.

Processing mediated enhancement of ferroelectric and electrocaloric properties in Ba(Ti0.8Zr0.2)O3–(Ba0.7Ca0.3)TiO3 lead-free piezoelectrics

High-performance Ba(Ti0.8Zr0.2)O3–(Ba0.7Ca0.3)TiO3 (BCZT) fiber crystals were grown using laser-heated pedestal growth (LHPG) for a systematic investigation of processing effects on structure and physical properties. By changing the growth rate (200−5 mm/h), fiber crystals with varying stoichiometry were realized: controlled composition, Ba0.872Ca0.128Ti0.925Zr0.075O3-δ, for the optimized crystal (5 mm/h), relative to the ceramic sample (SS) synthesized by the ceramic method. SS and optimized fibers exhibited larger energy storage densities of 700 and 868 mJ/cm3, respectively. Electrocaloric (EC) measurements by direct and indirect methods yielded ΔT of 1.3 K & 0.95 K and EC responsivity (ΔT/ΔE) of 0.3 and 0.43 K mm/kV for SS and 5 mm/h respectively, at 30 kV/cm, at least two-folds higher compared to 200 mm/h fiber. The EC responsivity of our samples is comparable to that of Pb(Mg,Nb)O3 crystals. These results demonstrate that BCZT has potential application as EC elements when the composition is controlled by fine-tuning of growth parameters.

Optical and scintillation properties of Ce:Y3Al5O12 single crystal fibers grown by laser heated pedestal growth method

The single crystal scintillating optical fibers acting as the scintillators and light conductors show potential application in scintillating fiber array detectors with high spatial resolution. In this paper we report the growth of 0.2 at% Ce:Y3Al5O12 single crystal fiber. The crystalline phase, surface morphology of the axial-section and cross-section, optical and scintillation properties of the as-grown fiber were investigated. The Ce:Y3Al5O12 single crystal fiber has a pure YAG phase, a uniform distribution of cerium in the axial-section and cross-section surface. Emission spectrum is composed of broad bands ranging from 440 to 700 nm. In addition, the single crystal fiber has a high light yield of 26115 ± 2000 photons/MeV, low energy resolution of 9.44% @662 keV and decay time of a fast component of 78 ns and a slow component of 301 ns. The intensity ratio of fast to slow components is roughly 8:1.

Monocrystalline fiber growth technique: New critical radius considerations

Laser-heated pedestal growth (LHPG) is an advantageous technique for crystalline fibers pulling due to its fast growth rate, related to the high axial thermal gradient. However, internal cracks can occur if the radius of the fiber is greater than the so-called thermal critical radius. For this reason, it is important to accurately determine the maximum axial thermal gradient to obtain crystalline fibers free of cracks. Herein, we improved the current method for critical radius determination by considering that the maximum temperature gradient is not present in the liquid/solid interface, but occurs directly on fiber, at a certain distance Δ from the liquid/fiber interface. In order to evaluate such improvement, cracks-free fibers of SrTiO3 (Melting Point = 2353 K) and Al2O3 (2345 K) were grown with this new criterion.

Epitaxial Growth of Single Crystal YAG for Optical Devices

We report the latest progress on fabrication of rare earth doped single crystal yttrium aluminum garnet (YAG) core/undoped YAG cladded fibers. Rare-earth doped single crystal core fibers were grown with laser heated pedestal growth methods. In a second step, epitaxial methods were used to grow a single crystalline undoped YAG cladding onto the core fiber. Hydrothermal and liquid phase epitaxy methods utilize the core doped fiber as the seed. X-ray diffraction of cladding reveals an equilibrium (110) morphology. Energy-dispersive X-ray spectroscopy analysis shows there is minimal diffusion of rare-earth dopants into the cladding structure. The use of scandium doping is shown to substitute at the Al3+ site, thereby allowing an additional tunability of refractive index of core structure material besides conventional Y3+ site dopants. The use of these epitaxial growth methods enables material compatibility, tuning of refractive index, and conformal growth of cladding structures onto core fibers for optical devices.

Broadband Single-Mode Cr-Doped Crystalline Core Fiber With Record 11-dB Net Gain By Precise Laser-Heated Pedestal Growth and Tetrahedral Chromium Optimization

We demonstrate a record net gain of 11-dB in a 34-cm fiber length for 300-nm broadband single-mode Cr-doped crystalline core fibers (CCFs) fabricated by precise laser-heated pedestal growth (LHPG) and tetrahedral chromium (Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> ) optimization. The core composition of the CCF is a Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> -doped: yttrium aluminum garnet (YAG). The record gain achieved is mainly due to (1) precise LHPG of the CCFs to fabricate a longer fiber length of 34-cm employing a novel predictive control to constantly maintain conical molten-zone shape in the growth process and (2) the Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> concentration optimization up to 150% utilizing thicker dielectric coating and thermal annealing and then the Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> optimization by polarization pumping. The net gains of 6.4 and 11-dB are measured with and without Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> optimization, respectively. The 72% of net gain improvement is directly related to Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> optimization in the CCFs, as evidenced by SQUID and EPMA measurements, whereas the optimized thicker coating of the Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> concentration provided the dominant net gain improvement of 33% in the CCFs. The development of the CCF is essential for practical use in the next-generation broadband fiber amplifier applications.

Near-infrared broadband emission from glass-clad Cr-doped yttrium orthosilicate crystal fiber

Cr4+:Y2SiO5 crystal fiber was grown by the laser-heated pedestal growth method. Severe spinodal decomposition domains were observed at low growth speed. At a growth rate of 30 mm/min, the spinodal decomposition area ratio was reduced to 0.4%. Using borosilicate as the cladding, 0.85 mW of broadband emission with a 3-dB bandwidth of 246 nm centered at 1257 nm was generated. The near-infrared light source is eminently suitable for optical coherence tomography with reduced scattering for deep tissue penetration. The estimated axial resolution is 2.8 µm in free space.

Спектроскопия иттриевого скандата, легированного ионами тулия

The thulium-doped yttrium scandate crystal fiber has been obtained by the laser-heated pedestal growth method. The crystal belongs to the bixbyite type, has a cubic structure and crystallizes in the Ia3 space group. The lattice parameters (a=10.224(1) Angstrem) have been determined using the powder X-ray diffraction. Spectral-kinetic measurements have allowed to detect two symmetrically independent optical centers of Tm3+ ions in the crystal fiber.

Laser Floating Zone Growth: Overview, Singular Materials, Broad Applications, and Future Perspectives

The Laser Floating Zone (LFZ) technique, also known as Laser-Heated Pedestal Growth (LHPG), has been developed throughout the last several decades as a simple, fast, and crucible-free method for growing high-crystalline-quality materials, particularly when compared to the more conventional Verneuil, Bridgman–Stockbarger, and Czochralski methods. Multiple worldwide efforts have, over the years, enabled the growth of highly oriented polycrystalline and single-crystal high-melting materials. This work attempted to critically review the most representative advancements in LFZ apparatus and experimental parameters that enable the growth of high-quality polycrystalline materials and single crystals, along with the most commonly produced materials and their relevant physical properties. Emphasis will be given to materials for photonics and optics, as well as for electrical applications, particularly superconducting and thermoelectric materials, and to the growth of metastable phases. Concomitantly, an analysis was carried out on how LFZ may contribute to further understanding equilibrium vs. non-equilibrium phase selectivity, as well as its potential to achieve or contribute to future developments in the growth of crystals for emerging applications.

Growth of High-quality Yb3+-doped Y3Al5O12 Single Crystal Fiber by Laser Heated Pedestal Growth Method

Growth of High-quality Yb³⁺-doped Y₃Al₅O₁₂ Single Crystal Fiber by Laser Heated Pedestal Growth Method

Growth of Tm:Lu3Al5O12 single crystal fiber from transparent ceramics by laser-heated pedestal method and its spectral properties

Abstract Tm:Lu3Al5O12 (Tm:LuAG) single crystal fiber (SCF) with a diameter of 0.6 mm and a length of 140 mm was grown from transparent ceramics by laser-heated pedestal growth (LHPG) method. The growth, Tm3+ ion distribution, absorption spectrum, Judd-Ofelt (J-O)parameter and emission spectrum of SCF are discussed in detail. The test results show that the diameter fluctuation of the SCF is less than 2% and the Tm3+ ion distribution is relatively uniform. J-O theory was applied to analyze the absorption spectrum. With the J-O intensity parameters Ωt(t=2,4,6), the emission probabilities, fluorescence branching ratios and radiative lifetimes for the Tm:LuAG SCF and transparent ceramic were all calculated. The stimulated emission cross-section of the3F4→3H6 transition was obtained by using the Fuchtbauer-Ladenburg (F-L) method. After comparison, it is found that the spectral performance of Tm:LuAG SCF has been improved to a certain extent on the basis of transparent ceramics. It has the potential to be applied to fiber lasers.

Dopant segregation in YAG single crystal fibers grown by the laser heated pedestal growth technique

In this study, we report self-segregation of dopants in a crystal matrix within a single crystal (SC) fiber. Neodymium and holmium-doped yttrium aluminum garnet (YAG) fibers were grown using the Laser Heated Pedestal Growth (LHPG) technique and cross-sectional dopant concentration was measured using electron-probe micro-analysis. It was observed that the degree of auto-segregation of the rare-earth dopant depended on the difference in ionic size of the dopant ion and the Y3+ ion in the YAG matrix. While holmium showed little tendency to self-segregate, the concentration of neodymium ions varied as much as 25% across the cross-section of the fiber. Strong correlation between the dopant concentration profile and fiber draw speed was also demonstrated. Since the local refractive index depends on the concentration of dopants, a refractive index profile can be achieved by a dopant profile across the fiber cross-section. Engineered index profiles can be realized by varying growth conditions, dopants, crystal matrix, etc. Such an approach is promising in applications such as the development of monolithic SC fibers with graded-index profiles.

Growth and Characterization of Neodymium-Doped Yttrium Scandate Crystal Fiber with a Bixbyite-type Crystal Structure

A crystal fiber of yttrium scandate YScO3 doped with Nd3+, with a cubic bixbyite-type crystal structure, has been synthesized through laser-heated pedestal growth for the first time. Its crystal st...