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Czochralski Growth and Characterization of Incongruent Melting LaGdSc(BO) (x +y + z = 4) Nonlinear Optical Crystal x

y

z

3

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Lucian Gheorghe, Federico Khaled, Alexandru Achim, Flavius Voicu, Pascal Loiseau, and Gerard Aka Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.6b00446 • Publication Date (Web): 09 May 2016 Downloaded from http://pubs.acs.org on May 10, 2016

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Crystal Growth & Design

Cover Page Title: Czochralski Growth and Characterization of Incongruent Melting LaxGdyScz(BO3)4 (x +y + z = 4) Nonlinear Optical Crystal. Authors: Lucian Gheorghe*♣, Federico Khaled♦, Alexandru Achim♣, Flavius Voicu♣, Pascal Loiseau♦, Gérard Aka♦ Affilations: ♣ National Institute for Laser, Plasma and Radiation Physics, ECS Laboratory, PO Box MG-36, 077125 Magurele, Romania ♦ Chimie ParisTech, PSL Research University, CNRS, Institut de Recherche de Chimie Paris, 75005 Paris, France Abstract: Incongruent melting nonlinear optical (NLO) crystals of LaxGdyScz(BO3)4 (x + y + z = 4) - LGSB have been grown by the Czochralski method, for the first time to our knowledge. The crystal growth conditions are discussed and the melt composition and growth parameters were optimized. The chemical composition of the best quality grown crystal was determined to be La0.64Gd0.41Sc2.95(BO3)4. It crystallizes in the non-centrosymmetric space group R32 (Z = 3) with cell dimensions a = 9.794(4) Å and c = 7.961(6) Å. The transmission window and refractive indices were measured and the phase-matching curves for type-I and type-II second harmonic generation (SHG) and (ω + 2ω) sum frequency generation (SFG) have been determined based on Sellmeier equations.

LGSB crystal grown along c-axis. Side view (left) and bottom view (right), parallel and normal to the growth direction, respectively. *Corresponding author: Dr. Lucian GHEORGHE National Institute for Laser, Plasma and Radiation Physics ECS Laboratory 409 Atomistilor Street, Magurele, P.O. Box MG-36 077125, ROMANIA Fax:+40 21 457-4243 Phone: +40 21 457-4550, ext 2111; +40 722 19-3546 Web page: http://ecs.inflpr.ro/; http://www.inflpr.ro/ Email: [email protected]

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Czochralski Growth and Characterization of Incongruent Melting LaxGdyScz(BO3)4 (x +y + z = 4) Nonlinear Optical Crystal Lucian Gheorghe*♣, Federico Khaled♦, Alexandru Achim♣, Flavius Voicu♣, Pascal Loiseau♦, Gérard Aka♦ ♣

National Institute for Laser, Plasma and Radiation Physics, ECS Laboratory, PO Box MG-36,

077125 Magurele, Romania ♦

Chimie ParisTech, PSL Research University, CNRS, Institut de Recherche de Chimie Paris,

75005 Paris, France KEYWORDS: Crystal growth, Czochralski method, Rare-earth scandium borates, Nonlinear optical crystals

ABSTRACT: Incongruent melting nonlinear optical (NLO) crystals of LaxGdyScz(BO3)4 (x + y + z = 4) - LGSB have been grown by the Czochralski method, for the first time to our knowledge. The crystal growth conditions are discussed and the melt composition and growth parameters were optimized. The chemical composition of the best quality grown crystal was determined to be La0.64Gd0.41Sc2.95(BO3)4. It crystallizes in the non-centrosymmetric space group R32 (Z = 3) with cell dimensions a = 9.794(4) Å and c = 7.961(6) Å. The transmission window and refractive indices were measured and the phase-matching curves for type-I and type-II second harmonic


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generation (SHG) and (ω + 2ω) sum frequency generation (SFG) have been determined based on Sellmeier equations.

INTRODUCTION According to the anionic group theory1, the nonlinear optical (NLO) borate crystals containing parallelly aligned BO3 anionic groups are suitable candidates for NLO applications due to their large NLO coefficients, moderate birefringence and wide transparency in the UV region. The natural mineral huntite, with chemical formula CaMg3(CO3)4 and space group R32, is the structural prototype for a wide variety of LnM3(BO3)4 (Ln = lanthanide or yttrium, M = Al, Ga, Sc) non hygroscopic borate crystals with favorable arrangement of their BO3 structural units.2,3 The most known member of this family is YAl3(BO3)4 (YAB) because it presents the highest nonlinear efficiency and a quite high laser damage threshold.3,4 YAB crystal was mainly studied as self-frequency doubling crystal, with Nd3+ or Yb3+ as doping ions, allowing the achievement of good results in this type of application.5-7 Even though YAB crystals have to be grown by the flux method, which makes them limited in size most often, the major impediments in the development of YAB crystals are due to the difficulties in the crystal growth and obtaining crystals of high quality. Moreover, the incorporation of flux components into the crystal (such as Fe, Mo…) gives rise to absorption bands in the UV range, limiting important applications at short wavelengths.3,8,9 To overcome these crystal growth problems, efforts have been directed to the development of related Sc huntite derivatives LnSc3(BO3)4 (Ln = lanthanide).10-12 LnSc3(BO3)4 borates crystallizes in different polymorphic forms depending on the ratio of the ionic radii of Ln and Sc (rLn/rSc). Thus, for Ln = La, LaSc3(BO3)4 - LSB compound is centrosymmetric (monoclinic structure, space group C2/c)12 and show therefore no χ(2) - based


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nonlinear effects, while for Ln = Gd, GdSc3(BO3)4 - GSB compound is isostructural with noncentrosymmetric trigonal huntite mineral (space group R32) and consequently allows χ(2) - based nonlinear effects.13 Nevertheless, the monoclinic structure of LSB can be converted to the trigonal form by doping with smaller lanthanide ions, such as La1-xNdxSc3(BO3)4,14 LaxYyScz(BO3)4 or LaxLuyScz(BO3)4 (x + y + z = 4).15,16 Moreover, (La1-xGdx)Sc3(BO3)4 single crystals of acentric space group R32 (for x > 0.2) have recently been obtained using the flux method,17 and the authors have shown that in this case Gd atoms substitute exclusively the La atoms. Although LSB compound has a non-congruent melting behavior, Ivonina et al.10 have succeeded to grow LSB crystal by the Czochralski method for the first time in 1991. More recently, Durmanov et al.12 have grown using the Czochralski method various rare-earth doped or co-doped LSB crystals having different types of crystalline structures depending on the ratio between the average ionic radius of rare-earth ions in the Ln site and rSc. They have also shown that the melt composition must have an excess of LaBO3 (or scandium borate deficiency) to obtain good quality crystals. Based on these previous studies, the growth of LaxGdyScz(BO3)4 (x + y + z = 4) - LGSB crystals by the Czochralski method was successfully investigated in the present paper. NLO crystals of good optical quality with dimensions of about 12 mm in diameter and 30 mm in length were obtained for the first time, to the best of our knowledge. The chemical composition and the compositional uniformity along the growth direction were determined for the best quality grown crystal. The main optical properties such as transmission window and refractive indices were measured, and the phase-matching curves for type-I and type-II second harmonic


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generation (SHG) and (ω + 2ω) sum frequency generation (SFG) were calculated based on Sellmeier equations. EXPERIMENTAL SECTION Material Synthesis. Considering La3+, Gd3+ and Sc3+ ions in the 6-fold coordination (ionic radii of 1.032, 0.938 and 0.745 Å, respectively),18 in a first approximation, we can assume that Gd3+ doping ions occupies La3+ sites rather than Sc3+ sites in the LGSB compounds. Therefore, in order to establish the minimum Gd content that determines the obtaining of single trigonal phase of LGSB, the general formula of the LGSB compounds was first approximated as La1xGdxSc3(BO3)4

(0 < x < 1). In this aim, polycrystalline samples of La1-xGdxSc3(BO3)4 with x =

0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 were prepared by solid-state reaction. The raw materials were 5N purity La2O3, Gd2O3, Sc2O3 and 99.98% purity B2O3. An excess of 5 wt% B2O3 with respect to the stoichiometric quantities was added to compensate for evaporation losses during sintering. Moreover, La2O3, Gd2O3 and Sc2O3 powders were fired at 1000°C for 12 h. Then, all compounds were weighed according to their formulas, mixed by grinding, cold-pressed into cylindrical pellets, and heated at 1300°C for 24h. All heating and preheating treatments were performed in air. The raw materials for the growth of LaxGdyScz(BO3)4 (x + y + z = 4) crystals were synthesized in similar conditions. X-ray Powder Diffraction. The X-ray powder diffraction (XRPD) patterns were recorded with a Bruker AXS D8 ADVANCE X-ray diffractometer (Cu Kα = 1.5406 Å). The measurements were carried out at room temperature in the angular range of 2θ = 10° - 80° with a scan step of 0.01° and a fixed counting time of 29.5s/step.


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Crystal Growth. LaxGdyScz(BO3)4 (x + y + z = 4) crystals with different compositional parameters x, y and z were grown by the Czochralski method in an inductively heated furnace. The growth of good optical quality LGSB crystals requires the optimization of both the melt composition and the growth parameters (pulling and rotation rates). In order to reduce the B2O3 evaporation, and also to prevent the vapors condensation on the surface of the growing crystal, several heating assemblies were experimented. The composition of the melt is one of the key elements to obtain good quality LGSB crystals. In accordance with the results obtained on rareearth doped or co-doped LSB crystals,12 LaxGdyScz(BO3)4 melt compositions with scandium deficit (z < 3) were investigated. The growth experiments were performed under N2 atmosphere from Ir crucibles of 30 mm in height and diameter. The growth temperatures determined by an infrared pyrometer were in the range of 1480 - 1510°C. The pulling and rotation rates were optimized in the range of 1 - 2 mm/h and 5 - 10 rpm, respectively. The diameter of the growing crystal, and implicitly the equilibrium temperature between the solid and liquid phase, was controlled by adjusting the crucible temperature based on direct visualization of the solid-liquid interface during all the period of the crystal pulling process. Lowering the heating power accelerates the crystallization and lead to an increased diameter, while increasing the power decrease the diameter of the growing crystal. The crystals were cooled to room temperature with a low cooling rate of 25°C/h to reduce stress and avoid cracks after growth. The chemical composition and the compositional uniformity of the grown crystal were determined by means of Inductively Coupled Plasma - Atomic Emission Spectrometry (ICP-AES) elemental analysis. Optical Characterization. The fundamental beam of 1064 nm from a pulsed Nd: YAG laser Q-smart 850 (10Hz, 850 mJ@1064 nm, pulse duration 6 ns) has been used to test the SHG property of synthesized materials and grown crystals. The optical transmission spectrum of


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LGSB crystal was measured at room temperature using a Varian Cary 5000 UV-Vis-NIR (2003000 nm) spectrophotometer. By using the minimum deviation method, the refractive indices were measured using a prism cut and oriented (apex angle = 59o33') from the as-grown crystal. Various gas-discharge lamps (Cd, Na, Hg, Hg/Cd/Zn) over the visible range and an optical parametric oscillator (OPO) laser system (EKSPLA model-NT342B) were used to measure the values of refractive indices as function of wavelength. RESULTS AND DISCUSSION The room temperature XRPD patterns of La1-xGdxSc3(BO3)4 synthesized compounds with different compositional parameter x are presented in Figure 1. As it can be observed, the structural change of La1-xGdxSc3(BO3)4 compounds from monoclinic (space group C2/c) to trigonal (space group R32) is complete for a Gd content larger than 30 at%. When the phase transition occurs, several diffraction peaks characteristic to monoclinic phase (marked with stars in Figure 1) disappeared. Although the trigonal phase R32 was found to characterize La1xGdxSc3(BO3)4

with x ≥ 0.2 by Xu et al,17 our experiments proved that the amount of Gd should

be larger than 30 at%. The SHG experiments of the fundamental wavelength of 1064 nm in La1xGdxSc3(BO3)4

synthesized compounds with x > 0.3 have confirmed their capability to generate

green (532 nm) emission.


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Figure 1. X-ray powder diffraction patterns of La1-xGdxSc3(BO3)4 synthesized compounds. The peaks marked with stars are characteristic to monoclinic phase of LSB,19 and the vertical sticks correspond to the peaks of the trigonal phase.14 Because LGSB crystals are peritectic compounds, the key to directly crystallize from the melt the trigonal phase R32 lies to use an excess of LaBO3-GdBO3 in the initial melt.12 Therefore, the target composition of the melt lies between points P and E in the assumed phase diagram (La,Gd)BO3-ScBO3 depicted in Figure 2.


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Figure 2. Assumed binary phase-diagram of (La,Gd)BO3-ScBO3. Based on the CeBO3-ScBO3 phase diagram published by Durmanov et al.12 The composition of the melt can be expressed as in Eq. 1: 3-x 3

Lay Gd1-y Sc3 BO3 4

4x 3

Lay Gd1-y BO3 Lay Gd1-y 1x Sc3-x BO3 4

Eq.1

In order to determine the minimal amount of “flux” LaBO3-GdBO3 to lie between the eutectic and peritectic points in Figure 2, several samples of (La0.6Gd0.4)1+xSc3-x(BO3)4 with 0 ≤ x ≤ 0.3 were prepared by solid-state reaction. After sintering, the samples were grounded and placed in Pt crucibles (3 - 4 cm in diameters). Then all samples were heated from room temperature to 1550°C and cooled down to room temperature twice. The heating and cooling rates were 10°C/min. From the XRPD measurements shown in Figure 3, the calcite phase ScBO3 (space


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group 3) is no longer present for x ≥ 0.2. Based on these results, we can expect to grow LGSB crystals with trigonal phase R32 from a melt containing more than 20 at% of (La,Gd)BO3.

Figure 3. X-Ray Powder Diffraction patterns of the (La0.6Gd0.4)1+xSc3-x(BO3)4 for x = 0.0, 0.1, 0.2 and comparison with the reference pattern of pure trigonal R32 LGSB sample. Because they are peritectic compounds, the liquid and the growing crystal have not the same composition. Therefore, high thermal gradients are needed to stabilize the growth interface. However, the use of high thermal gradients leads to evaporation and a change of the melt composition, which is not wanted. As a conclusion, to avoid constitutional supercooling, a compromise should be found to ensure the growth.12 In this work, several heating assemblies which allow to control efficiently the described processes were designed and experimented for the growth of LaxGdyScz(BO3)4 (x + y + z = 4) crystals with scandium deficit (z < 3) in the starting melt. Three of them are presented in Figure


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4. For each heating assembly, the crystal growth conditions are discussed and the starting melt composition and growth parameters were optimized to obtain good optical quality NLO crystals of LGSB.

Figure 4. Heating assemblies designed and experimented for the growth of LGSB crystals.

The first heating assembly (Figure 4a) has as originality: a continuous flow of N2 during the crystal pulling and in the first part of the crystal cooling process until the remaining melt is solidified, which has the role to remove B2O3 vapors directly from the growing crystal, based on gas convective flow around the crystal and at the melt surface. By using this heating assembly, several LGSB crystals have been grown from different starting melt compositions. Three of the grown crystals are shown in Figure 5. A crystalline LGSB seed with unknown orientation was used in all growth processes. The best results in terms of crystal transparency were obtained for


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the melt composition La0.75Gd0.5Sc2.75(BO3)4 by using the optimized pulling and rotation rates of 1.5 mm/h and 10 rpm, respectively (Figure 5c). However, when the crystal is illuminated with an infrared source at 1064 nm a green light is observed in all directions reflecting no doubt the presence of defects such as fine twins which diffract the light like a grating, similar to Y0.57La0.72Sc2.71(BO3)4 - LYSB and YAB huntite-type borate crystals.20

Figure 5. LGSB crystals grown by using the first heating assembly (Figure 4a) from the starting melt compositions (a) La0.5Gd0.6Sc2.9(BO3)4, (b) La0.625Gd0.625Sc2.75(BO3)4 and (c) La0.75Gd0.5Sc2.75(BO3)4.

Compared with the first heating assembly, the originality of the second heating assembly (Figure 4b) consists in the addition of a drilled Pt ring which aims to reduce the thermal gradients over and in the melt. The distance between the top of the crucible and the Pt ring is about 2 mm. Based on the results obtained by using the first heating assembly with respect to crystal transparency, scattering defects and preliminary tests related to SHG property of


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synthesized materials and grown crystals, an intermediate starting melt composition between the compositions presented in Figure 5b and 5c, respectively, was selected to be grown by using this second assembly. Thereby, several LGSB crystals have been grown with different growth parameters from the starting melt composition La0.678Gd0.572Sc2.75(BO3)4. The best quality crystal was obtained for pulling and rotation rates of 1.8 mm/h and 10 rpm, respectively, and also in this case the crystal was grown on a crystalline LGSB seed with unknown orientation. The photograph of the as-grown crystal (inside of the growth chamber) is shown in Figure 6. Like all other grown crystals, it has typical dimensions of about 12 mm in diameter and 30 mm in length. The experiments on SHG of 1064 nm fundamental laser beam have still revealed the presence of scattering defects, but at a lower level than in the case of first heating assembly.

Figure 6. LGSB crystal grown by using the second heating assembly (Figure 4b) from the starting melt composition La0.678Gd0.572Sc2.75(BO3)4. A third heating assembly (Figure 4c) was also experimented for the growth of LGSB crystals from the same La0.678Gd0.572Sc2.75(BO3)4 starting melt composition. In this case, the N2 flow was eliminated (the growths were performed in an enclosed N2 atmosphere) and a drilled


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Al2O3 ring was added to reduce much more the temperature gradients. The distance between the top of the crucible and the Al2O3 ring is about 20 mm. By using this heating assembly, good quality NLO crystals of LGSB, without scattering defects, were obtained at relatively high pulling rate of 2 mm/h and low rotation speed of about 8 - 10 rpm. The growth morphology and quality of the grown crystals are dependent on the growth direction. The best quality crystals were obtained using - oriented seeds (parallel to the c- or Z-axis), and the as-grown crystal has regular hexagonal shape with well-developed {2 1 1 0} and {1 1 2 0} faces. The photograph of one of the LGSB crystals grown along c-axis is shown in Figure 7. The following investigations in this work were carried out on this crystal.

Figure 7. LGSB crystal grown along c-axis by using the third heating assembly (Figure 4c). Side view (left) and bottom view (right), parallel and normal to the growth direction, respectively. Figure 8 shows the X-ray powder diffraction pattern of c-axis grown LGSB crystal together with the ICDD pattern 01-080-3941 relative to the trigonal huntite-type phase of LGSB published by Xu et al (space group R32, a = 9.7933(7)Å, c = 7.9540(12)Å).17 The X-ray analyses show all the diffraction peaks of LGSB are in agreement with those of huntite structure and no additional peaks were found. From the X-ray pattern, the unit cell parameters of LGSB crystal were calculated to be a = 9.794(4) Å and c = 7.961(6) Å.


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Figure 8. X-ray powder diffraction pattern of LGSB crystal. Blue vertical sticks refer to the ICDD 01-080-3941 pattern. The optical transmission spectrum of a 2.5-mm-thick (0 0 1) - cut LGSB crystal sample was measured in the wavelength range of 200 - 3000 nm and is presented in Figure 9. The transmission spectrum shows that LGSB crystal has a wide transparency wavelength range, with a cut-off wavelength of about 230 nm, which makes it very promising for a variety of NLO applications, especially in the visible and UV spectral regions. The UV cut-off wavelength is a little bit higher from the 190 nm value that has been reported previously for LYSB or LGSB crystals obtained by the top-seeded solution growth (TSSG) method.15,17


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Figure 9. Transmission spectrum of LGSB crystal (thickness of 2.5mm). The inset figure shows the transmission spectrum in the UV region. We have examined the compositional uniformity along the growth direction by the ICP-AES method at the Service Central d’Analyse - Institut des Sciences Analytiques (Vernaison, CNRS). on samples from the shoulder, body, and tail of the LGSB crystal from Figure 7. The results are summarized in Table 1. We can see that the crystal composition is homogenous along the crystal length, and that the ratio La/Gd is higher in the crystal than in the melt, meaning that the distribution coefficient of Gd in the LSB compound is less than 1. Within the measurement error of ± 0.2%, the chemical composition of LGSB crystal was determined to be La0.64Gd0.41Sc2.95(BO3)4. Moreover, our results confirm that the Gd atoms do substitute mainly the La atoms, because the stoichiometry of scandium is close to 3.


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Table 1. Stoichiometry of the LGSB crystal based on the ICP-AES elemental analysis. Composition of the LGSB crystal

Ratio of La/Gd

Starting melt

La0.678Gd0.572Sc2.75(BO3)4

1.18

Shoulder

La0.640Gd0.414Sc2.946(BO3)4

1.55

Body

La0.642Gd0.408Sc2.950(BO3)4

1.57

Tail

La0.638Gd0.442Sc2.920(BO3)4

1.44

The refractive indices of LGSB crystal of Figure 7 were measured by the minimum deviation technique using a prism cut from the grown crystal with two faces polished to the optical quality. The orientation of the prism is shown in Figure 10.

Figure 10. Prism cut and oriented from the LGSB crystal. From the measured values of the refractive indices, reported in Table 2 and Figure 11, LGSB is a negative uniaxial crystal (no > ne). The experimental data points were fitted with Sellmeier equations in Eq. 2 and Eq. 3 (Estimated standard deviations (esd) are indicated in round brackets):


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n λ 3.317 3

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. ! "

− 0.024 2λ

Eq. 2

. -. "

− 0.009 2,

Eq. 3

#$ %

*+ , 3.027 3 /$ %

. &' !

. && !

Table 2. Refractive indices data for LGSB crystal. Measurement by the minimum deviation method (accuracy of 0.0001) and calculations from Sellmeier equations (Eq. 2 and Eq. 3). n0

ne

Wavelength (µm) Measurement

Calculation

Measurement

Calculation

0.3550

1.8970

1.8971

1.8048

1.8052

0.4358

1.8694

1.8693

1.7817

1.7818

0.4678

1.8623

1.8622

1.7757

1.7759

0.4722

1.8612

1.8614

1.7748

1.7752

0.4811

1.8599

1.8597

1.7738

1.7738

0.5086

1.8551

1.8551

1.7700

1.7699

0.5320

1.8518

1.8518

1.7671

1.7671

0.5461

1.8501

1.8500

1.7657

1.7656

0.5770

1.8464

1.8464

1.7627

1.7627


18

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0.5893

1.8452

1.8452

1.7617

1.7616

0.6328

1.8415

1.8413

1.7583

1.7584

0.6438

1.8406

1.8404

1.7579

1.7577

1.0640

1.8214

1.8216

1.7435

1.7437

1.2000

1.8180

1.8179

1.7415

1.7414

Figure 11. Refractive indices measurements for LGSB crystal along with the Sellmeier fit of the experimental data. Compared to YAB crystal, LGSB exhibits a wider birefringence (∆n = 0.078 at 1064 nm compared to 0.071 for YAB).21 However, due to the high dispersion of the values in the UV


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range, the cut-off wavelength for type-I SHG is only 570 nm for LGSB (see Figure 12) compared to 490.5 nm for YAB.21 Therefore, 4th harmonic generation at 266 nm (by SHG of 532 nm) is not possible in LGSB crystal. Nevertheless, as we can see in Figure 13, light at 355 nm can be obtained by type-II SFG (eoe) of 1064 nm and 532 nm in LGSB crystal with a phasematching angle of 65.5°.

Figure 12. Calculation of the phase-matching curves for type-I and type-II SHG in LGSB crystal. Calculations derived from the Sellmeier equations.


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Figure 13. Calculation of the phase-matching curve for type-I and type-II (ω + 2ω) SFG in LGSB crystal. Calculations derived from the Sellmeier equations. Compared to the previous data published on LGSB,17 we found that the phase matching angle for type-I SHG at 1064 nm is 35.8° instead of 34.8°. The difference may be due to a large number of experimental points, but is more likely due a slight difference of the chemical composition: as a matter of fact, the ratio of La/Gd in the crystal is found to be about 1.6 compared to more than 3.5 for Xu et al.17 Some nonlinear parameters (walk-off angle, angular and spectral acceptances) can be derived from the refractive indices measurements and are compiled in Table 3. The nonlinear properties found in this work are similar to that of previous data published,17 and are comparable to YAB nonlinear properties.21 Table 3. Quick comparison of nonlinear properties between LGSB and YAB crystals for type-I SHG at 1064 nm.


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LGSB LGSB17

YAB21

(35.8°, 60°)

(34.8°, 60°)

(30.8°, 60°)

0.078

0.078

0.071

2.60

2.55

2.23

0.030

0.030

0.035

0.79

0.71

1.43

Crystal [This work] Phase-matching angles (θ, φ) Birefringence ∆n Walk-off angle ρ (o) External angular acceptance ∆θ.L (°.cm) Spectral acceptance ∆λ.L (nm.cm)

CONCLUSIONS Incongruent melting nonlinear optical crystals of LaxGdyScz(BO3)4 (x + y + z = 4) - LGSB were grown by the Czochralski method, for the first time to our knowledge. Different heating assemblies were designed, and good optical quality NLO crystals of LGSB with relatively large


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size (about 12 mm in diameter and 30 mm in length) were obtained. The melt composition and growth parameters were optimized and the best quality crystal was grown along c-axis direction from La0.678Gd0.572Sc2.75(BO3)4 starting melt composition at pulling and rotation rates of 2 mm/h and 8 - 10 rpm, respectively. The chemical composition of the grown crystal was determined to be La0.64Gd0.41Sc2.95(BO3)4. It is non hygroscopic and X-ray analysis showed that it crystallizes in the non-centrosymmetric space group R32 (Z = 3) with cell dimensions a = 9.794(4) Å and c = 7.961(6) Å. The transmission window and refractive indices were measured and SHG and (ω + 2ω) SFG phase-matching properties were reported. The main nonlinear properties of our LGSB crystal are compared with those of flux - grown LGSB and YAB crystals. These favorable characteristics coupled with the opportunity to grow large dimension LGSB crystals by the Czochralski method, make them very promising for NLO applications, especially for frequency conversion of high-average power laser beams in the visible and UV wavelength ranges.

AUTHOR INFORMATION Corresponding Author *Phone: + 40 21 4574550, + 40 21 4574558 ext 2111. E-mail: [email protected], [email protected]

ACKNOWLEDGMENT This work was supported by the Romanian Ministry of National Education, MEN-UEFISCDI, Partnerships in priority areas, PN-II-PT-PCCA-2013-4-1488 under grant agreement no.10/2014, Romanian National Authority for Scientific Research, CNCS-UEFISCDI, PN-II-ID-JRP-2011-1


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under grant agreement no. 3 RO-FR/03.01.2012, and French National Research Agency, ANR, Programme Blanc International II - SIMI 4 - Physique (Blanc Inter II SIMI 4) 2011, under grant agreement ANR-11-IS04-0006. Authors would like also to thanks the French DIMOxyMORE network for supporting this research.

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(12) Durmanov, S. T.; Kuzmin, O. V.; Kuzmicheva, G. M.; Kutovoi, S. A.; Martynov, A. A.; Nesynov, E. K.; Panyutin, V. L.; Rudnitsky, Yu. P.; Smirnov, G. V.; Hait, V. L.; Chizhikov, V. I. Opt. Mater. 2001, 18, 243-284. (13) Wang, G.; Gallagher, H. G.; Han T. P. J.; Henderson, B. J. Cryst. Growth 1996, 163, 272278. (14) Li, Y; Aka, G.; Kahn-Harari, A.; Vivien, D. J. Mater. Res. 2001, 16, 38-44. (15) Ye, N.; Stone-Sundberg, J. L.; Hruschka, M. A.; Aka, G.; Kong, W.; Keszler, D. A. Chem. Mat. 2005, 17, 2687-2692. (16) Li, W.; Huang, L.; Zhang, G.; Ye, N. J. Cryst. Growth 2007, 307, 405-409. (17) Xu, X.; Ye, N. J. Cryst. Growth 2011, 324, 304-308. (18) Shannon, R. D. Acta Crystallogr. 1976, A 32, 751-767. (19) Goryunov, A. V.; Kuzmicheva, G. M.; Mukhin B. V.; Zharikov, E. V.; Ageev, A. Y.; Kutuvoi, S. A.; Kuzmin, O. V. Zh. Neorg. Khim. 1996, 41, 1605-1611. (20) Maillard, A. A.; Maillard, R. S.; Loiseau, P.; Aka, G.; Villeval, P.; Rytz, D. Advanced Solid State Lasers, OSA Technical Digest (online) 2014, paper ATh2A.12. (21) Yu, J.; Liu, L.; Zhai, N.; Zhang, X.; Wang, G.; Wang, X.; Chen, C. J. Cryst. Growth 2012, 341, 61-65.


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For Table of Contents Use Only

Czochralski Growth and Characterization of Incongruent Melting LaxGdyScz(BO3)4 (x +y + z = 4) Nonlinear Optical Crystal Lucian Gheorghe*♣, Federico Khaled♦, Alexandru Achim♣, Flavius Voicu♣, Pascal Loiseau♦, Gérard Aka♦

Synopsis Nonlinear Optical Crystals are used in various applications, and among them borate compounds are supposed to be the best candidate for high conversion efficiency with high average output power. The present paper deals with the Czochralski growth of an incongruent-melting binary rare-earth scandium borate which presents huntite-type structure.


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Czochralski Growth and Characterization of ... - ACS Publications

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