Top-seeded Solution Growth Method Research Articles

First Achievement of Yellow Laser Operation in Dy3+-Doped Borate Crystals.

Continuous-wave (CW) yellow lasers have been demonstrated successfully by using a GaN laser-diode (LD) pumping in borate crystals for the first time. The Dy3+:GdMgB5O10 (Dy:GMB) crystal with dimensions up to 33 × 19 × 15 mm3 is grown by the top-seeded solution growth method, and the polarized spectroscopic properties are investigated systematically at room temperature. The line strengths, Judd-Ofelt (J-O) intensity, spontaneous transition rates, fluorescence branching ratios, and radiative lifetimes are calculated in detail by the Judd-Ofelt theory. Under direct pumping of 452 nm LD, a compact continuous-wave yellow laser with a maximum output power of 628 mW and laser wavelength of 581 nm is generated based on a Y-cut Dy:GMB crystal. To our knowledge, it is not only the highest output power for yellow laser obtained in Dy3+-doped crystals but also the first yellow laser operation achieved by borate crystals under direct LD pumping. The results reveal that the Dy:GMB crystal is an optical material with important application prospects in yellow laser.

Cu-doped KTN crystal with controllable, reversible, and fast photochromic properties: A superior electro-optical material for improving beam deflection performance

Improving the deflection performance of a beam deflector is urgently required to acquire optical signals for space laser communication and change the attitude and position of space targets and spacecraft. In this work, a Cu-doped potassium tantalate niobate (Cu-KTN) single crystal with fast photochromic and increased beam deflection properties is synthesized using the top-seeded solution growth method. When a Cu-KTN single crystal is irradiated with 405 nm light or ultraviolet (UV) light, the color changes from pale green to reddish brown. After light irradiation, the color gradually returns to yellowish green. Decolorization is accelerated under irradiation with green light or long-wavelength light, and the color changes to pale green. The origin of reversible photochromism reveals the fast valence change of Cu ions. In addition, ion doping improves the beam deflection angle of the secondary electro-optical effect of Cu-KTN (4.3 mrad, 1000 V) crystal compared with pure KTN (3.2 mrad, 1000 V). This study successfully synthesizes Cu-KTN single crystals with photochromic uses and establishes a new route for beam deflectors with significant deflection angles.

Growth and magnetocaloric effect of Na2Gd2(BO3)2O crystal

High-quality Na2Gd2(BO3)2O crystals have been successfully grown using the top-seeded solution growth method (TSSG), employing a Na2O - NaF - B2O3 flux system with optimal molar ratios of Na2Gd2(BO3)2O : Na2CO3 : NaF : H3BO3 = 1:2:6:4. The magnetic and magnetocaloric properties were investigated including magnetic susceptibility (χ), magnetization (M), and isothermal magnetic entropy change (−ΔSm) measurements. Na2Gd2(BO3)2O exhibits a large magnetocaloric effect with a maximum − ΔSm of 41.6 J·kg−1·K−1 at 2 K and 7 T, which is higher than that of commercial Gd3Ga5O12 (GGG, −ΔSm = 38.4 J·kg−1·K−1 at 2 K and 7 T) and most other Gd3+-based borates, showing the potential application in the field of magnetic refrigeration.

Analysis of Macrostep Interaction via Carbon Diffusion Field in SiC Solution Growth

In the top-seeded solution growth (TSSG) method for SiC, control of macrostep development is crucial for improving the crystal quality. Dislocation conversion phenomena caused by macrosteps with a certain height on the crystal surface can reduce the dislocation density, while over-developed macrosteps bring macroscopic defects such as solvent inclusions. It is experimentally reported that solution flow direction to the step movement has a substantial impact on the macrostep development: parallel solution flow promotes and anti-parallel solution flow suppresses the increase of macrostep height. Our hypothesis is that this macrostep development is governed by the interaction between the macrosteps not by the instability of the density of the atomical steps. In this study, we constructed a computational fluid dynamic model of the boundary layer around macrosteps on the crystal surface, incorporating the solution flow on the boundary layer and consumption of the carbon solute by the macrostep movement quantitatively. The computational simulation reveals that the macrostep with position shift from the center of the adjacent macrosteps moves to the direction of the nearer macrostep under the parallel flow and moves to the farther macrostep under the antiparallel flow. These macrostep movements result in the bunching and debunching of the macrosteps. The mechanisms of macrostep movements demonstrated in this study will be useful for the precise control of macrostep height aiming to the reduction of the dislocation density during SiC solution growth.

Li3Na7B4P6O26: a new ultraviolet transparent congruently melting non-linear optical crystal.

The exploration of nonlinear optical crystals with ultraviolet (UV) transparent ranges and easy-to-grow large-size crystals is one of the current research interests. Herein, by combining borate and phosphate groups, a novel congruently melting alkali-mixed metal borophosphate, Li3Na7B4P6O26 (LNBPO) with UV transparency was successfully designed and synthesized using a high-temperature flux method. LNBPO crystallizes in the non-centrosymmetric (NCS) and polar orthorhombic space group Pca21 (no. 29), showcasing interesting (B2P3O13)∞ chains along the c axis. Notably, LNBPO has a moderate second harmonic generation (SHG) response (∼0.38 × KDP) and displays a wide transmission ranging from 0.22 to 3.68 μm, as measured by a [001]-oriented crystal wafer. Furthermore, a high-quality single crystal of LNBPO with sizes up to 14 × 14 × 12 mm3 was grown using the top-seeded solution growth method. The refractive indices of LNBPO were determined by applying the minimum deviation angle method. These results show that LNBPO possesses a phase-matching wavelength as short as 483 nm, indicating its potential as a new UV NLO crystal.

Novel laser crystal Lu2TeO6: crystal growth, thermal properties, and spectral analysis

In this paper, novel tellurate crystals Lu2TeO6 and Nd:Lu2TeO6 in a trigonal system are successfully grown by the top-seeded solution growth (TSSG) method using TeO2 and Li2CO3 as fluxes.

Enhanced piezoelectricity of Cu-doped K(Ta,Nb)O3 single crystals

As a class of solid solution material, K(Ta,Nb)O3 (KTN) single crystals have attracted significant interest due to their excellent piezoelectric and electro-optic performance. In this study, the piezoelectric properties of KTN were improved through Cu doping. Utilizing the advantages of composition-regulating phase transition, a large, high-quality Cu:KTN crystal measuring 30 mm × 25 mm × 20 mm in size was grown using the improved top seeded solution growth method. Cu-doped KTN exhibited better piezoelectric properties than pure KTN, and the full matrix parameters were investigated. Excellent dielectric, piezoelectric, and electromechanical coupling responses (ε11T∼ 2,136, d33∼303 pC/N, kt∼0.515, and k33∼0.672) were successfully obtained. To realize the optimized orientation of the piezoelectric properties, the orientation dependence of the single domain properties was investigated, and the mechanism of Cu doping to improve piezoelectric properties was explored. We found that 0.36% (in mass) Cu doped crystal consisted of A-site substitution, following ferroelectric and domain analysis. The small ferroelectric domain sizes led to a large domain wall mobility rate and high domain wall density, which contributed to high piezoelectric properties. This work revealed the effect of A-position doping on piezoelectric properties and provided a theoretical and experimental foundation for the performance optimization of KTN-based materials.

Growth and near-infrared optical properties of Nd3+-doped KGd0.1Lu0.9(WO4)2 crystal

In this paper, x at.% Nd3+: KGd0.1Lu0.9-x(WO4)2 (x = 1, 2, 3, 4, 5) crystals were grown by the top seed solution growth method (TSSG). The crystal structure was analyzed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR), and the crystal structure data was obtained by Rietveld refinement. The absorption spectra, near-infrared emission spectra and fluorescence decay curves of Nd3+ ions in the crystal were measured at indoor temperature. According to Judd-Ofelt theory, the spectral intensity parameters Ω2, Ω4 and Ω6 are calculated. When the doping concentration is 3 at.%, Ω2 is the largest, which is 3.84 × 10−20 cm2, while the spectral mass factor is the lowest, which is 0.3734. The absorption and emission cross-section are calculated by combining the absorption spectrum and emission spectrum, and the maximum calculated result of emission cross-section is 1.35 × 10−19 cm2. The results show that Nd3+: KGd0.1Lu0.9(WO4)2 crystals has great application potential in the 1.0 µm field.

Effect of Ca2+ ions on structure and spectroscopic properties of Er3+: KBaY(MoO4)3 crystals

This study successfully grew KBaY(MoO4)3 crystals doped with single Er3+ ions and co-doped with Ca2+/Er3+ ions using the top-seeded solution growth method. Thermal analysis of the KBaY(MoO4)3 crystals was performed by differential scanning calorimetry, and their phase and structure were characterized using X-ray diffraction and Fourier transform infrared spectroscopy. The luminescent properties of the crystals in the visible and near-infrared wavelength ranges under different concentrations of Er3+ ions were analyzed through emission spectroscopy, and the concentration quenching mechanism was investigated in depth. The results showed that the strongest emission intensity was obtained at an Er3+ ion concentration of 5 mol%. Additionally, by substituting Ba2+ ions with Ca2+ ions, the emission intensity was significantly enhanced, especially when the Ca2+ ion doping concentration reached 6 mol%, resulting in the maximum emission intensity. Furthermore, we investigated the effects of matrix structure and lattice distortion on the spectral properties by employing Judd-Ofelt (J-O) theory and studying energy transfer mechanisms. The mechanisms of Ca2+-induced fluorescence quenching and factors influencing the fluorescence decay time were analyzed. Through the analysis of the absorption cross-section, emission cross-section, and gain cross-section of crystals with different Ca2+ ion concentrations, it was found that Ca2+, Er3+: KBYM crystals exhibited a low laser pump threshold. The results demonstrate that the 6 mol% Ca2+, 5 mol% Er3+: KBYM crystals possess excellent performance and are a promising laser gain medium.

Spectral properties and theoretical analysis of Dy3+:KGd(WO4)2 crystals in the visible wavelength band

Yellow laser has been widely applied in various fields such as biomedicine, optical communication technology and chip processing. This study focuses on the preparation and characterization of a 3 at.% Dy3+:KGd(WO4)2 crystal. The crystal was grown by the top-seeded solution growth method. The absorption spectrum, excitation spectrum, emission spectrum, and fluorescence decay curve were measured at room temperature, and the fluorescence properties of the crystal in the yellow region were explored. Analysis of the absorption spectrum revealed an absorption cross-section σabs of 4.81 × 10−21 cm2 at 453 nm (E//Y), corresponding to the 6H15/2 → 4I15/2 transition. Utilizing the Judd-Ofelt theory, the J-O intensity parameters Ωt, radiative transition probability, fluorescence branching ratio, and radiative lifetime were calculated. The F-L theory was used to calculate the emission cross-section σem at 575 nm (E//Y), which was found to be 2.43 × 10−20 cm2, along with a fluorescence lifetime τf of 148.5 μs and a fluorescence quantum efficiency of 80.35% for 4F9/2. These findings suggest that Dy3+:KGd(WO4)2 crystal shows significant promise as a yellow laser material, with the potential to contribute to both commercial and scientific fields.

Growth of ferroelectric lithium niobate-tantalate LiNb(1-x)TaxO3 crystals

Congruent and stoichiometric ferroelectric lithium niobate-tantalate crystals LiNb(1-x)TaxO3 of different compositions were grown by the Czochralski method. The stoichiometric crystals were grown using the top seeded solution growth method using LiWO4, which increases the Li content in the melt and in the grown crystal. Also, the use of a solvent can significantly reduce the temperature of the melt. The composition of the crystals was studied by inductively coupled plasma mass spectrometry using laser ablation, which allow studying the change in the composition of the grown crystals along the length and diameter. It is demonstrated that the content of Ta in the crystals exceeds the content of Ta in the initial charge, i.e., in the process of crystal growth, the melt becomes depleted in Ta. It is shown that the Ta content decreases along the crystal length due to the decrease in the Ta content in the melt. In the LiNb0.88Ta0.12O3 crystals, the piezoelectric moduli d22 and d33, and the velocities of bulk and surface acoustic waves were measured. The values of piezoelectric moduli and acoustic wave velocities are shown to occupy an intermediate position between LiNbO3 and LiTaO3 crystals.

Evidence of Yb3+ band broadening and continuous wave laser operation in bismuth modified KY1-x-yBixYby(WO4)2 mixed single crystals

To increase the Yb3+ optical bandwidths in highly anisotropic β:KY(WO4)2 (KYW) type laser single crystals, the simultaneous contributions of the Bi3+ 6 s2 lone electron pair and Y3+/Bi3+ ionic radii mismatch is proposed. The top seeded solution growth method with K2W2O7 as solvent was used to grow Yb doped single crystals of the KY(WO4)2/KBi(WO4)2 (KYBiW) solid solution. Crystals obtained across the used KY1xBixW solid solution range show always the low temperature β phase, with the monoclinic C2/c crystalline structure, but important differences between the Y/Bi composition of the starting solute and that of the crystal grown are found. The incorporation of Y and Yb into the crystal is preferential, resulting in a low Bi segregation coefficient, SBi= 13%, on the KYW side but near SBi= 90% in the KBiW side (Yb is still strongly incorporated filling the remaining 10%). The saturation temperature of the melt decreases as the Bi concentration in the precursor KY1-x-yBixYby(WO4)2/K2W2O7 mixture increases. Evidence of optical absorption and photoluminescence broadening of the Yb3+ bands with Bi3+ incorporation is derived from 6 K and 300 K measurements. Laser operation of KY1-x-yBixYby(WO4)2 crystals is shown to be comparable to that of KY1−yYby(WO4)2 ones. Up to ≈ 0.5 W of output power is obtained pumping in continuous wave regime with a Ti sapphire laser with slope efficiency η ≈ 65% and pump threshold< 200 mW, which is within the usual performance of KYW:Yb crystals, but the spectral distribution of the laser output in KYBiW:Yb crystals is larger than that for KYW:Yb. This spectral broadening may help in the reduction of ultrashort (fs) laser pulse duration generated by modelocking.

Crystal growth and spectral properties of Eu3+-doped La2CaB10O19 single crystals

The invention and commercial application of InGaN/GaN-laser diodes have made it feasible to directly obtain the visible lasing radiation by pumping rare earth (RE) doped laser crystals. Hence searching for new laser crystals with efficient luminescence and applicable optical and physical properties in the visible range is an essential work. Here, the crystal growth and spectral properties of a series of large-size Eu3+ doped La2CaB10O19 (Eu3+-LCB) single crystals with the nominal atomic ratios of 3%, 7%, and 10% have been well studied. High-quality Eu3+-LCB single crystals with the size of 45 × 30 × 17 mm3, was grown by top-seeded solution growth (TSSG) method. The luminescence probe was employed as the tool to identify occupation sites, demonstrating that Eu3+ ions enter into La3+ sites first, then occupy Ca2+ sites after the nominal atomic ratio of Eu3+ ions exceeds 7%. Based on the absorption and emission spectra, the intensity parameters, spontaneous transition probability, radiation lifetime, and fluorescence branch ratio for Eu3+-LCB single crystals are studied with the Judd–Ofelt theory. From the transient spectra, the emission cross-section, fluorescence decay lifetime and luminescence quantum efficiency are deduced, which exhibit the maximum performance at the nominal atomic ratio of 7% Eu3+. Combining the luminescence probe and spectral properties, it can be concluded that Eu3+ doped crystals will have the best spectral properties when Eu3+ occupation at the single La3+ sites reaches the maximum in LCB single crystals, which may be universal for RE-doped crystal with two possible occupation sites. Besides, our work demonstrates that the 7% Eu3+-LCB single crystal may be a promising medium for laser radiation in the visible region in comparison with other Eu3+ doped single crystals.

Growth and magneto-optical properties of Bi25FeO40 crystals with heavy Co/Fe co-doping

This paper focuses on the magneto-optical properties of sillenite Bi25FeO40 crystals rather than optofractive, optoelectronic, piezoelectric and other properties. The Bi25FeO40 crystals with heavy Co3+ and Fe3+ co-doping were successfully grown into centimeter size by the top-seeded solution growth method. The thermal stability of crystal structure was improved. Annealing in oxygen atmosphere can greatly reduce oxygen vacancy defects, thereby improving the transmittance of the crystal. After doping Co3+ and Fe3+, Fe-O-Fe, Fe-O-Co and Co-O-Co superexchange interactionis formed in the crystal, which greatly enhances the magnetism of the crystal. Not only the magnetic but also the magneto-optical properties were significantly enhanced by co-doping Co3+ and Fe3+.

Flux growth of nonlinear optical crystal K3B6O10Br with high optical quality and its electro-optical property

Nonlinear optical (NLO) crystal, simultaneously exhibits second-harmonic generation response and linear electric-optical (EO) susceptibility, is of great significance for optoelectronics due to its frequency extension technique and optical modulation effect. In this paper, the growth system of K3B6O10Br (KBB) crystal in the green-flux K2MoO4–KBF4 was systematically investigated to get rid of the non-intrinsic absorption in the ultraviolet wavelength range, which is beneficial for high-power applications. Bulk KBB NLO crystals were successfully grown by the top-seeded solution growth method from different fluxes for comparison. Moreover, the electro-optical (EO) property of KBB crystal was explored, and the effective EO coefficient γ22 along transverse modulation was determined to be 1.10 p.m./V.

Nd3+-Doped La2CaB8O16 Crystals for Orthogonally Polarized Dual-Wavelength Near-Infrared Lasers

The Nd3+-based laser crystal is one of the key gain media for all-solid-state laser technology. Herein, by investigating the relationship between structure and optical properties, we found that a La-containing borate, La2CaB8O16, with a long rare-earth ion distance more than 4.27 Å, allows a high doping concentration and exhibits a weak fluorescence quenching effect. For the first time, Nd3+-doped La2CaB8O16 crystals with different concentrations were grown by the top seeded solution growth method with large size and high optical quality. Its spectral characters were measured, suggesting a strong absorption band at 800 nm and a fluorescence band at 1055 nm. Furthermore, a diode-pumped orthogonally polarized dual-wavelength laser operation at 1052 and 1055 nm was realized, with a slope efficiency of 16.3% and output power of 859 mW. These results suggest that the Nd3+-doped La2CaB8O16 crystal is a promising laser gain medium for 1 μm lasers and possible generation of terahertz radiation.

Crystal growth and negative thermal expansion properties of a Y2Mo4O15 single crystal.

A bulk-size single crystal of Y2Mo4O15 with 20 × 11 × 8 mm3 was successfully grown by the top-seed solution growth (TSSG) method. The full-width at half maximum of (100) and (010) crystal faces is 37 and 27 arcsec, respectively. The thermal conductivity coefficients κ 11, κ 22, κ 33, and κ 13 are determined to be 1.519, 2.097, 0.445, and 0.997 W m-1 K-1, respectively. It is worth noting that the Y2Mo4O15 crystal shows significant anisotropy thermal expansion properties, which exhibits a negative thermal expansion along the b-axis (α 22 = -5.11 × 10-6 K-1). The crystal structure analysis shows that the shrinking of Mo-O bond lengths along the b-axis with the increasing temperature would be the main origin of the negative thermal expansion properties for Y2Mo4O15 crystal, which does not comply with the current mechanism.

Crystal growth and thermal properties of a LiY(MoO4)2 crystal

A high-quality tetragonal LiY(MoO4)2 single crystal was grown by a top-seeded solution growth method. Based on the quality evaluation, the optical transmission and thermal properties of the LiY(MoO4)2 single crystal were fully characterized.

Linear and nonlinear optical properties of trigonal borate crystals K7MIn2−xYbx(B5O10)3 (M = Ca, Sr, Ba; x = 0…2) with isolated B5O10 units

Noncentrosymmetric borates K7MIn2−xYbx(B5O10)3 (M = Ca, Sr, Ba; x = 0…2) were synthesized by the solid state reaction and the crystals were successfully grown by the top seeded solution growth method using the K2O-B2O3-MF2 flux. According to Rietveld refinement, the crystal structure belongs to the noncentrosymmetric R32 space group. Also, the octahedrally coordinated In atoms are located at wide ranges ∼8 Å which may be promising for phosphor and laser applications. Samples with ytterbium show a characteristic emission band in the range of 950–1050 nm related to the 2F5/2 → 2F7/2 transition of Yb3+ ions that is commonly used for laser generation. IR, Raman and absorption spectra were obtained for the samples as well. The short cut edge of UV absorption, SHG intensity comparable with KDP and low concentration quenching of luminescence suggest that the K7MIn2−xYbx(B5O10)3 borates are promising self-frequency doubling materials.

Growth and characterizations of a new nonlinear optical crystal for 266 nm laser generation: LiSr3Be3B3O9F4

The LiSr3Be3B3O9F4 (LSBBF) single crystal with dimensions of 30 × 20 × 15 mm3 was grown from a LiF-NaBF4-B2O3-SrF2 flux system using a top-seeded solution growth method with a seed perpendicular to the (011) plane. The X-ray rocking curve, transmission spectra, refractive indices and laser-induced damage threshold have also been studied. The Sellmeier equations were derived from the measured refractive indices for the first time. According to the Sellmeier equations, the limits of type-I and type-II phase-matching (PM) frequency doubling wavelengths are 241 and 318 nm, respectively. It indicates that LSBBF is a potential UV nonlinear optical crystal for the fourth harmonic generation of Nd:YAG laser at 266 nm.