Laser-heated Pedestal Growth Method Research Articles

Optical temperature sensing characteristics of Yb3+/Nd3+ co-doped YAG single crystal fiber based on up-conversion luminescence

YAG: 5 mol%Yb3+/x mol%Nd3+(x = 0, 0.5, 1, 2, 4, 7) and YAG: 2 mol%Nd3+ single crystal (SC) fluorescent materials were prepared using laser heated pedestal growth (LHPG) method. The up-conversion (UC) spectra of YAG: Yb3+/Nd3+ were recorded under 980 nm laser excitation, the results show that the optimal material was obtained at 5 mol%Yb3+/2 mol%Nd3+. An integrated YAG single crystal fiber (SCF) with end 5 mol%Yb3+/2 mol%Nd3+ co-doped was prepared by the LHPG method, the temperature-dependent characteristics were measured in the range from 348 K to 1448 K. It shows that the fluorescence intensity increases and then decreases with the increase of temperature. Fluorescence intensity ratios (FIR) in Nd3+ UC spectra, including FIR1 (4F7/2/4F5/2 → 4I9/2), FIR2 (4F9/2/4F5/2 → 4I9/2) and FIR3 (4G5/2/4F9/2 → 4I9/2), vary monotonically in temperature ranges of 348–1273 K, 523–1273 K, and 673–1273 K, respectively. The maximally absolute and relative sensitivities for FIR1 were, respectively, achieved to be 2.34 × 10−3 K−1 at 738 K and 4.61 × 10−1 %K−1 at 390 K, and these values for FIR2 were accordingly achieved to be 1.19 × 10−3 K−1 at 1273 K and 4.59 × 10−1 %K−1 at 735 K, and for FIR3 they were 4.66 × 10−3 K−1 at 1273 K and 4.09 × 10−1 %K−1 at 760 K. Therefore, we believe that the fabricated YAG: Yb3+/Nd3+ fluorescent materials have favorable application potential for optical thermometer.

Directional and lattice engineering growth of sapphire fibers for ultrasonic ultra-high-temperature sensors

High-temperature sensors for extreme environments are in urgent demand with the rapid development of aerospace, nuclear energy, and advanced manufacturing. Ultrasonic temperature sensors (UTS) are widely used in high-temperature sensing due to their high working temperature that approaches the melting point of the acoustic waveguide. Al2O3 single-crystal fiber (SCF), also called sapphire fiber, is a promising candidate for ultrasonic thermometry due to its ultra-high melting point (∼2050 °C), high strength and oxidation resistance. Here, we report for the first time, to the best of our knowledge, large length-diameter ratio sapphire fibers with specific orientations (a-axis, m-axis, and c-axis) have been grown by laser-heated pedestal growth method and applied for ultrasonic temperature sensing. Sapphire fibers exhibit significant acoustic anisotropy, and a-oriented sapphire fiber has a lower acoustic velocity and a greater velocity-temperature variation, leading to higher sensitivity. Moreover, the acoustic velocity of sapphire fiber could be further decreased by doping with Cr ions owing to the enhanced lattice disorder and crystal density. As a result, an improved unit sensitivity of 28.98–52.88 ns°C−1m−1 and a superior resolution of 1.73–0.95 °C have been achieved in the range of 20–1200 °C via a-oriented Cr:Al2O3 SCF-UTS. More importantly, the sensor performance is positively correlated with ambient temperature, accompanied with the high working temperature (∼1800 °C) and excellent stability (∼20 h), demonstrating promising prospects for applications in high-temperature thermometry. This work provides a feasible approach for designing a high-performance UTS based on acoustic anisotropy and lattice engineering.

Light response uniformity of LuAG:Ce scintillating single crystal fiber grown by laser heated pedestal growth method

Own to its fine granularity and sub-millimeter position information, scintillating single crystal fibers (SSCFs) hold great potential for various applications such as electromagnetic calorimeters, positron emission tomography, and radiotherapy dosimetry. The light response uniformity of scintillating fibers is an important parameter for precise measurements of ionizing radiation. Three methods were designed to investigate the light response uniformity of the 184-mm-long LuAG:Ce SCCF. Relatively longitudinal-distributed uniformity of cerium element was obtained in this SSCF. The scintillation light attenuation coefficient of the SSCF is 0.27 cm−1 induced by X-ray photons with single-end readout mode and about 0.29 cm−1 induced by gamma rays with dual-end readout mode. The Ce3+ ions self-absorption along the longitudinal light propagation process is one of main reasons for the scintillation light attenuation. Weakening the Ce3+ ions’ self-absorption effect is a possible way to improve the light response uniformity of the LuAG:Ce SSCF.

Growth, spectroscopy properties and laser operation of a novel single crystal fiber: Nd3+-doped CaY0.9Gd0.1AlO4

A Nd3+-doped CaY0.9Gd0.1AlO4 single crystal fiber (Nd: CYGA SCF) with a length of 80 mm and a diameter of 1 mm, to the best of our knowledge, was successfully grown for the first time by a highly efficient laser-heated pedestal growth method. The basic physical and chemical properties, optical properties, and laser properties of the as-grown SCF were studied in detail. The results show that the Nd: CYGA SCF has wider absorption and emission half-peak full width compared with a bulk single crystal. Furthermore, under the pumping of a commercial 808 nm laser diode, a CW laser operation at 1080 nm with a half-height width of 0.29 nm was obtained. The laser output power was 54 mW at an absorbed power of 2.03 W. The slope efficiency was 6.79% with respect to the absorbed pump power. Thus, the Nd: CYGA SCF might be a practical and powerful candidate for laser gain medium, and have a great research space in the field of lasers.

Spectral study and energy transfer analysis of Er:YAlO3 crystals

Er:YAP crystals have been proved promising mid-infrared gain materials but there is few systematic study focused on the relationship between the doping concentration and spectral properties. In this work, Er:YAP crystals with a series of doping concentrations(0.1 at.%, 1 at.%, 5 at.%, 10 at.%, 15 at.%, 30 at.%) were fast grown successfully by a modified laser-heated pedestal growth (LHPG) method. Through investigating doping concentration dependent spectral characteristics in detail, we found that the cross relaxation process (Er3+: 4S3/2+4I15/2 → 4I9/2+4I13/2) gets significantly enhanced with the doping concentration when it is below 5 at.%, and eventually tends to saturate. And the cooperative up-conversion process (Er3+: 4I13/2+4I13/2 → 4I15/2+4I9/2) conducive to high-efficiency ∼3 μm laser starts to dominate when the doping concentration is 5 at.% or even less. This result demonstrates the potential of Er:YAP crystals to achieve high-power and high-efficiency laser output under relatively low Er-doping concentration, and offers a valuable guidance for doping optimization of Er:YAP systems.

Growth of a Gradient-Doped Single-Crystal Rod with Designable Distribution of Doped Ions by a Laser-Heated Pedestal Growth Method

Growth of a Gradient-Doped Single-Crystal Rod with Designable Distribution of Doped Ions by a 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

Aluminum garnet crystal has great potential in detecting the high-energy photons and particles for its good scintillation properties and preparing the high time and spatial resolution fiber-array detector for its' easy preparation as single crystal fiber. 0.2 at% Ce: Lu1-xYxAG (x = 0, 0.25, 0.5, 0.75, 1) scintillating single crystal fibers were successfully prepared by laser heated pedestal growth method. The 5d1 energy level of Ce3+ luminescence center is shifting to lower energy and 5d2 energy level of Ce3+ luminescence center is shifting to higher energy with the Y admixture increasing. The photoluminescence decay was fitted by single-exponential decay curve and the scintillation decay were fitted by double-exponential decay curve instead for the different luminescence mechanism. The highest scintillation light yield of 32,457 Ph/MeV and 10,617 Ph/MeV was obtained from the horizontal-direction and longitudinal-direction sides of 0.2 at% Ce: Lu0.25Y0.75AG scintillating single crystal fiber respectively, demonstrating its perspective for application in High Energy Physics.

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

Spectroscopy of the yttrium scandate doped by thulium ions

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. Keywords: bixbyite, optical center, rare-earth ion, laser-heated pedestal growth.

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.

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.

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 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.

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.

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.

Cracking mechanism and spectral properties of Er,Yb:CaGdAlO4 crystals grown by the LHPG method

High quality Er,Yb:CaGdAlO4 (Er,Yb:CALGO) single crystals with a diameter around 1 mm were successfully grown and investigated for the first time by the laser heated pedestal growth (LHPG) method.

Wide-range temperature sensor based on enhanced up-conversion luminescence in Er3+/Yb3+ co-doped Y2O3 crystal fiber

Abstract The Y2O3:Er3+/Yb3+ crystal fiber material has been successfully prepared by laser heated pedestal growth method. The X-ray diffraction results indicate that the prepared Y2O3:Er3+/Yb3+ luminescent material, which is optically transparent under the optical microscope, possesses pure Y2O3 crystal phase. The up-conversion luminescence corresponding to the (2H11/2, 4S3/2, 4F9/2) → 4I15/2 transitions of Er3+ ions were recorded under a 976 nm laser diode excitation. The up-conversion emission intensities from the 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions of Er3+ ions were studied from room temperature to 873 K by fluorescence intensity ratio (FIR) technique. It has been found that the prepared Y2O3:Er3+/Yb3+ crystal fiber has high-efficient up-conversion emissions, and effectively improves the temperature measurement accuracy and range, making Y2O3:Er3+/Yb3+ crystal fiber an interesting candidate for optical temperature sensor.

The characteristics of high-quality Yb:YAG single crystal fibers grown by a LHPG method and the effects of their discoloration.

Single crystal fibers (SCFs), especially ytterbium (Yb) doped crystal fibers, have great potential in the field of high-power lasers. Colorless Yb:YAG single crystal fibers were fabricated using a laser heated pedestal growth (LHPG) method with a diameter fluctuation of less than 2% and a length to diameter ratio greater than 320 : 1. An abnormal color issue exists with respect to Yb:YAG crystals. The origin of coloration was studied via density functional theory, single-crystal X-ray diffraction, XPS and Raman spectroscopy and it was confirmed that the cyan coloration of Yb:YAG crystals is due to oxygen vacancies. Yb:YAG SCFs prepared via the LHPG method could avoid this type of defect due to the large specific surface area and melt convection caused by surface tension. The fundamental properties of the cyan Yb:YAG crystal source rod and colorless Yb:YAG SCFs were systematically investigated. The colorless Yb:YAG SCFs have higher infrared transmittance and thermal conductivity. The distributions of Yb3+ along the radial and axial directions were also measured. Meanwhile we demonstrated the propagation loss and a fiber laser using the colorless Yb:YAG SCFs, obtaining a minimum loss coefficient of 0.008 dB cm−1 and a maximum continuous-wave (CW) output power of 3.62 W. The colorless Yb:YAG SCFs with good thermal conductivity, low propagation loss, wide transparency and uniform ion distribution show promise for acting as the host material in single-mode lasers.