Horizontal Directed Crystallization Method Research Articles

Optical and laser characteristics of Сo-doped magnesium-aluminum spinel crystals grown using molybdenum crucible

Single crystals of Co-doped magnesium-aluminum spinel (MALO:Co) are used for Q-switching of laser radiation at λ = 1.54 μm. Usually, they are grown by the Czochralski method from iridium crucibles that are too expensive. This investigation demonstrates the possibility of obtaining MALO:Co single crystals by the horizontal directional crystallization method using a molybdenum crucible in Ar + (CO, H2) protective reducing medium.The obtained MALO:Co crystals have the spinel structure of MgO‧xAl2O3 with 1 ≤ x < 1.15, and the impurity of molybdenum in them does not exceed 0.019 wt%. Co2+ ions replace Mg2+ ions in the [MgO4] tetrahedral environment. This is confirmed by the broad absorption bands (λmax ≈ 600 nm and λmax ≈ 1400 nm) in Vis-IR spectra. The absorption bands in the UV region of the spectrum are shown to originate from the complexes of point defects that can be eliminated by subsequent annealing in oxidizing/reducing environment. Experimentally shown is the possibility to obtain monoimpulses with the energy of ∼ 1–2 mJ and ∼10–15 ns duration at a wavelength of ∼1.54 μm in passive Q-switches based on MALO:Co crystals.

Ce3+ Doped Al2O3-YAG Eutectic as an Efficient Light Converter for White LEDs

Ce3+ doped Al2O3-YAG eutectics were successfully grown by the horizontal directional crystallization method. The crystallization rate of eutectic growth was changed in the 1-7.5 mm/h range at a growth temperature of 1835 ℃. The microstructure of eutectic samples was investigated using scanning electron microscopy and X-ray microtomography. The intrinsic morphology of eutectic represents the stripe-like channel structure with a random distribution of the garnet Y3Al5O12 (YAG) and Al2O3 (sapphire) phases. The content of these phases in the stripes changes in the 52.9-55.3% and 46.1-47.1% ratios, respectively, depending on the growth rate of the crystallization of the eutectic samples. The luminescent properties of the eutectic demonstrated the dominant Ce3+ luminescence in the garnet phase. The luminescence of the Ce3+ ions in Al2O3 has also been observed and the effective energy transfer processes between Ce3+ ions in the Al2O3 and YAG garnet phases were revealed under high-energy excitation and excitation in the UV Ce3+ absorption bands of sapphire. The phosphor conversion properties and the color characteristics (Al2O3-YAG):Ce eutectic with different thicknesses were investigated under excitation by a blue LED. We have also tested the prototypes of white LEDs, prepared using a blue 450 nm LED chip and (Al2O3-YAG):Ce eutectic photoconverters with 0.15 to 1 mm thicknesses. The results of the tests are promising and can be used for the creation of photoconverters for high-power white LEDs.

Optical, electrophysical and structural properties of polycrystalline germanium grown by horizontal directional crystallization method

Optical, electrophysical and structural properties of polycrystalline germanium grown by horizontal directional crystallization method

Horizontal Directed Crystallization: Fabrication and Characterization of High‐Dimension Single‐Crystal Yb:YAG Ingots Grown by Horizontal Directed Crystallization Method (Crystal Research and Technology 12/2020)

Horizontal Directed Crystallization: Fabrication and Characterization of High‐Dimension Single‐Crystal Yb:YAG Ingots Grown by Horizontal Directed Crystallization Method (Crystal Research and Technology 12/2020)

Fabrication and Characterization of High‐Dimension Single‐Crystal Yb:YAG Ingots Grown by Horizontal Directed Crystallization Method

AbstractThe research conducted herein builds upon the achievement of a successful and stable 170 × 300 × 35 mm YAG and 5% Yb:YAG single‐crystals production via the horizontal directed crystallization method. Based on the analysis of residual birefringence pattern in analyzed ingots, a hypothesis is proposed—debating that in certain stages of the growth, {211} facets start to form within some sections of the crystallization front. The sensitivity of the {211} facets to temperature fluctuations seems to cause striations in the facets’ growth sectors. In a later stage of the growth process the slope of the crystallization front naturally changes, which seems to reduce the formation of facets considerably. As a result, the rear part of the crystal achieves the best optical quality. The samples extracted from that portion of the ingot, after annealing, possess good optical quality and heat release of 0.004 1/m at 1070 nm, which is quite low, and is considered a good result for the garnet family of crystals. The lasing experiment with thin‐disk geometry shows a slope efficiency of 52% and proves that the material is suitable for high‐power lasers application.

Analysis of heat transfer processes for sapphire growth by horizontal directed crystallization method

This research summarizes the analytical and experimental results of heat-transfer processes influence on defects formation during sapphire crystal growth by horizontal directed crystallization method (HDC). The shape of solid-melt interface significantly influences the process of sapphire crystals growth by this method. We receive the Stefan problem solution for sapphire crystals growth. It allows investigating the crystal growth process and the related factors (thermal stresses on different stages of growth process), their influence on defects formation. We investigate the main reasons for the formation of defective structures of the solid phase of sapphire crystals and the influence of thermal unit construction, the crystal geometry on the quality of the resulting sapphire crystal. We study the structure formation process, impurity distribution, and the nature of the defects in the crystal during it growth.

An Analysis Approach to the Sapphire Crystals Growth by Horizontal Directed Crystallization Method

The model for sapphire crystals growth parameters estimation has been suggested. It can be served as a basis for the analysis of heat transfer processes during sapphire crystals obtaining. It allows to predict the bubbles, stresses and cracks appearing during sapphire crystals growth. We describe the results of the analysis and parameters estimation of sapphire crystals growth on all stages by horizontal directed crystallization method.

Computational approach to the simulation of sapphire crystals growth by horizontal directed crystallization method

In this article we present an integrated approach to sapphire crystals growth simulation. Thermally induced stresses in sapphire crystals growing by horizontal directed crystallization are simulated by finite element method. The simulation results correspond to experimental observations. The results of the investigation allow to improve the process of crystal growth to obtain high quality large sapphire crystal.

Optical and luminescence properties of Er,Yb:YAG crystals grown by horizontal directional crystallization method

Optical and luminescence properties of Er,Yb:YAG crystals grown by horizontal directional crystallization method

Investigation of Influence of Sapphire Crystals Shape Factor on Its Growth by Horizontal Directed Crystallization

The value of shape factor allows to determine what processes (the surface or in crystal volume) define the dynamics of sapphire crystal growth by horizontal directed crystallization method and, as a result, estimate the influence of these processes on crystal quality. We receive the Stefan problem closed solution for sapphire crystals growth by horizontal directed crystallization method. It allows to investigate the growth process and the related factors (thermal stresses on different stages of growth process), melt hydrodynamics and its influence on defects formation. 1.

Spectral properties of Er-doped yttrium aluminum garnet crystals grown by modified horizontal directional crystallization method

Spectral properties of Er-doped yttrium aluminum garnet crystals grown by modified horizontal directional crystallization method

Formation of longitudinal aggregation of inclusions in bulk sapphire and yttrium‐aluminum garnet grown by horizontal directed crystallization method

It is shown that the formation of longitudinal aggregation of inclusions in bulk sapphire and yttrium‐aluminum garnet (YAG) grown by the method of HDC is caused by local accumulation of impurities, disturbance of morphological stability of the crystallization front and capture of inclusions and impurities in the nodal region of the melt two‐vortex convection. Studied is the influence of thermal and geometrical parameters of the melt and the shape of the crystallization front on the conditions of the formation of the capture of inclusions.

Anomalous X-ray transmission through sapphire crystals

The triple-crystal X-ray diffractometry of anomalous X-Ray transmission is used to investigate sapphire single crystals grown in protective gaseous media with the help of the horizontal directional-crystallization method. The dependences between the integral intensities of anomalously transmitted and Bragg-Laue reflected X-ray beams (Ti and Ri, respectively) and the thickness of the samples under study, which enable us to determine regions of thin- and thick-crystal approximation, have been obtained at 2.52 ≤ μt ≤ 18.9. The integral coefficient μi of interference absorption and the integral characteristic yi are calculated in the dynamic thick-crystal approximation. It is demonstrated that dislocations are distributed mainly within the small-angle boundaries of a grown sapphire crystal. It is ascertained that the parameter μi is highly sensitive to the dislocation density and the pattern of the dislocation distribution in a crystal.

Growth and the luminescence properties of a lutetium gadolinium garnet doped with Ce3+ and Pr3+ ions

Crystals of lutetium gadolinium garnet solid solutions (Lu1 − x Gd x )Al5O12 (0 ≤ x ≤ 0.6) doped with Ce3+ and Pr3+ ions have been prepared by the horizontal directional crystallization method, and their optical and luminescence properties have been investigated. It has been established that the introduction of gadolinium into the lutetium garnet lattice leads to a decrease in the antisite luminescence (LuAl centers) in the UV spectral range and to sensitization of the Ce3+ ion luminescence. By contrast, the presence of gadolinium results in the quenching of the Pr3+ luminescence due to the nonradiative excitation transfer from Pr3+ ions to Gd3+ ions.

Spectral characteristics of neodymium-activated yttrium aluminum garnet in the ultraviolet and visible ranges

The absorption, photoluminescence, and x-ray luminescence spectra of pure and neodymium-activated YAG crystals grown by the horizontal directional crystallization method were investigated at 295°K in the wavelength range 190–900 nm. A particular study was made of wide strong absorption bands with maxima at 224 and 205 nm due to introduction of neodymium into YAG crystals. These bands were attributed to the 4f →5d transitions in Nd3+ ions localized at normal and anomalous structural positions. A system of luminescence bands observed in the 260–620 nm range excited by x-ray and hard (e >4.79 eV) photoexcitation of YAG:Nd was attributed to transitions from the 2F 25/2 (e =37 850 cm−1) level to levels of all the lower neodymium multiplets. In the case of excitation by softer photons (3.22 ≲ e ≲ 4.68 eV), the luminescence spectrum was due to transitions from another metastable level 2P3/2 (e =25 990 cm−1) to levels of lower terms. A new structural scheme was proposed for the formation of anomalous rare-earth ion centers in laser garnets.