Growth of (Er,Yb):YAl3(BO3)4 laser crystals

(Er,Yb):YAl₃(BO₃)₄ single crystals of optical quality, up to 15 × 10 × 10 mm³ in size, have been grown from a (Er_0.023Yb_0.116Y_0.862)Al₃(BO₃)₄ solution in a Y₂O₃-B₂O₃-K₂Mo₃O₁₀ melt. The initial borate concentration was 17 wt %, and the flux cooling rate increased from 0.08 to 0.12°C/h in the range 1060–1000°C. The physical properties of the single crystals grown are good enough that they can be used as laser elements in systems with diode pumping and radiation near 1.5 μm.     

The influence of Yb3+ concentration on Yb:YAl3(BO3)4

The Yb:YAl₃(BO₃) ₄ crystals with different Yb³⁺ doping concentration have been grown by the flux method. The lattice parameters and decomposition of the Yb:YAl₃(BO₃)₄ crystal with different Yb³⁺ doping concentration were measured by X‐ray and DTA method. The transmission and fluorescence spectra of Yb³⁺:YAl₃(BO₃)₄ crystal have been measured. The growth defects of Yb_xY_1‐xAl₃(BO₃)₄ crystals were also detected by using the chemical etching method. The results show that the ytterbium concentration influences these properties of Yb:YAl₃(BO₃)₄. As the Yb³⁺ concentration increased, the crystal lattice parameter was decreased. At high doping level, the absorption peak concerned at about 980 nm shift to short wavelength. It is also found that the perfection of Yb:YAl₃(BO₃) ₄ crystal with low Yb³⁺ doping concentration is better than that with high Yb³⁺ concentration. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Second harmonic generation in Na3Gd2(BO3)3 crystals

Na₃Gd₂(BO₃)₃ crystals with dimensions up to 22 × 20 × 5 mm³has been grown from NaBO₂ flux by the top‐seeded solution growth (TSSG) method for the first time. Differential scanning calorimetry (DSC) result shows that Na₃Gd₂(BO₃)₃ melts incongruently. The infrared spectrum indicates that Na₃Gd₂(BO₃)₃ contains characteristic triangular [BO₃]^3– groups responsible for the nonlinear optical effect. For the as‐grown crystal, the transmittance exceeds 80% in the wavelength range of 315 nm to 2670 nm, and the UV cutoff wavelength is 207 nm. The damage threshold is 0.47 GW cm^–2 at 1064 nm. Moreover, Na₃Gd₂(BO₃)₃ crystal exhibits an optical second harmonic generation effect which is 1.3 times as large as that of KH₂PO₄ (KDP). (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theoretical and experimental study on the conoscopic interference in uniaxial crystal (Ca0.28Ba0.72)x(Sr0.60Ba0.40)1‐xNb2O6

Conoscopic interference of polarized light for the white‐light and LPS‐7,5Volts direct current semiconductor laser (Green light) with wavelength at 532 nm in (Ca_0.28Ba_0.72)_x(Sr_0.60Ba_0.40)_1‐xNb₂O₆ crystals were observed with the beams transmitting along optical‐axes and deflection optical‐axes from 0 to 140°. Endo‐exo variation from looseness to tightness of conoscopic interference patterns were analyzed in theory. A hyperbolic black cross of interference patterns were observed as well as its formation process was proposed in this paper. Also, the inferences of the birefringence with different Ca²⁺‐doped were obtained in this investigation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Self‐diffraction and edge enhanced effect in the photorefractive crystal (Ca0.28Ba0.72)0.75(Sr0.60Ba0.40)0.25Nb2O6

The optical properties based on Self‐diffraction phenomena and the edge enhanced of optical correlation pattern effect with a Ca²⁺‐doped (Ca_0.28Ba_0.72)_0.75(Sr_0.60Ba_0.40)_0.25Nb₂O₆ (CSBN₇₅) crystals and a He‐Ne laser at 632.8 nm are studied in this paper. The experimental results show that its practical application as photorefractive material is worth further investigation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of Al2O3 addition on the formation of perovskite-type NaNbO3 nanocrystals in silicate-based glasses

The crystallization behavior of 30Na₂O–25Nb₂O₅–(45 ? x) SiO₂–xAlO_1.5 (x = 0, 2.5, and 5) (mol%) glasses was examined and the effect of Al₂O₃ addition on the formation of perovskite-type NaNbO₃ crystals was clarified. It is found from X-ray diffraction analyses and transmission electron microscope observations that NaNbO₃ nanocrystals are formed in all glasses and the size of NaNbO₃ crystals decreases with the substitution of Al₂O₃ for SiO₂. A crystallized (heat-treated at 684 °C for 5 h) glass with x = 5, which contains NaNbO₃ nanocrystals with an average size of 50 nm, shows good optical transparency in the wavelength region of 500–2000 nm and a small hysteresis loop in the polarization–electric field curve. The lines containing NaNbO₃ crystals were patterned on the surface of NiO-doped glass with x = 5 by irradiations (power: 1.3–1.4 W, scanning speed: 10 μm/s) of Yb:YVO₄ fiber laser (wavelength: 1080 nm). The formation mechanism of NaNbO₃ nanocrystals in aluminosilicate glasses was also discussed.     

Flux crystallization of trigonal GdFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> competing with the crystallization of α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

The formation of trigonal GdFe₃(BO₃)₄ crystals in the Bi₂Mo₃O₁₂-B₂O₃-Li₂MoO₄-Gd₂O₃-Fe₂O₃ system was studied. The flux compositions for which GdFe₃(BO₃)₄ is the high-temperature phase with a wide range of crystallization were determined. The features of nucleation of these crystals and their growth near the phase boundary with α-Fe₂O₃ were analyzed. The growth of GdFe₃(BO₃)₄ single crystals involving preliminary nonequilibrium crystallization of α-Fe₂O₃ is described.     

A new nonlinear optical crystal: Bi2O2(OH)(NO3)

The nonlinear optical (NLO) properties of Bi₂O₂(OH)(NO₃) crystals have been reported for the first time. Bi₂O₂(OH)(NO₃) crystals with dimensions of 1.3×1.2×0.1 mm³ have been grown by hydrothermal method, and the crystals characterized by X‐ray powder diffraction (XRD), SEM and IR. The measured second harmonic generation (SHG) effect of Bi₂O₂(OH)(NO₃) was about 7 times that of KDP. The mechanism responsible for the large SHG of Bi₂O₂(OH)(NO₃) was explained according to its structure. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High temperature synthesis and crystal structure of new representatives of the huntite family

Single crystals of REE, Al borates, new and known representatives of huntite family are obtained by annealing of REEBO₃ on Al₂O₃ surface at 1100°C. Phase identification for REE=Pr, Eu, Tb, Tm, Ho, Yb has been carried out using unit cell parameter determination on single crystals. Crystal structures of C 2/c (PrAl₃(BO₃)₄) and C 2 (EuAl₃(BO₃)₄) ‐ two polytypic modifications, previously determined for other REE's have been studied. Formation of one or another polytype in similar thermodynamic conditions is probably dependent on electronic structure of rare earth ion. Crystal field stabilization energy in crystal fields of different symmetry is a possible factor of polytype stability (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal structure of the new barium borate Ba5(BO3)2(B2O5)

The crystal structure of the new barium borate Ba₅(BO₃)₂(B₂O₅) is established (R = 0.0436). Single crystals were grown by spontaneous crystallization in the BaO-B₂O₃-Na₂O system using the flux method. This compound crystallizes in the orthorhombic system, sp. gr. P2₁2₁2₁; the unit-cell parameters are a = 9.590(2) Å, b = 16.659(3) Å, c = 22.919(6) Å, and Z = 12. The structure consists of coordination polyhedra of barium cations and the anionic groups [BO₃] (planar triangles) and [B₂O₅] (vertex-sharing double [BO₃] triangles), which form a pseudohexagonal framework. Melting of barium borate occurs by a peritectic reaction at 1170 ± 10°C.     

Recent advances in rare earth-based borate single crystals: Potential materials for nonlinear optical and laser applications

Due to an increase in the requirement for ultraviolet and visible laser sources nonlinear optical crystals are gaining importance. Borate-based nonlinear optical crystals such as lithium borate LiB₃O₅ (LBO), CsLiB₅O₁₀ (CLBO), SrBe₂B₂O₇ (SBBO), KBe₂BO₃F₂ (KBBF) and K₂Al₂B₂O₇ (KAB) have excellent transmission ranges extending from the ultraviolet into the infrared region. But their hygroscopic nature retards their use in real-time applications. Rare earth-based borate crystals such as rare earth calcium oxy borate RECa₄O(BO₃)₃ (RECOB) and rare earth calcium borate RE₂CaB₁₀O₁₉ (RECB) have excellent nonlinear optical behaviour and also allow the substitution of ‘laser-active’ ions to create ‘laser crystals’. Further they are non-hygroscopic which favours them in practical applications. A review on RECOB and RECB crystals is presented along with a discussion on our attempts to grow yttrium calcium oxy borate YCa₄O(BO₃)₃ (YCOB), lanthanum calcium oxy borate LaCa₄O(BO₃)₃ (LCOB), yttrium calcium borate Y₂CaB₁₀O₁₉ (YCB) and lanthanum calcium borate La₂CaB₁₀O₁₉ (LCB) crystals. These crystals possess excellent transmission properties combined with nonlinear optical behaviour. They also exhibit high laser damage threshold (LDT) values.     

Microwave dielectric properties of La(1‐2x/3)Bax(Mg0.5Sn0.5)O3 ceramics

This study examined the potential applications of microwave dielectric properties of La_(1‐2x/3)Ba_x(Mg_0.5Sn_0.5)O₃ ceramics in rectenna. The La_(1‐2x/3)Ba_x(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid‐state method with various sintering temperatures. An apparent density of 6.62 g/cm³, a dielectric constant of 20.3, a quality factor of 51,700 GHz, and a temperature coefficient of resonant frequency of ‐78.2 ppm/K were obtained for La_2.98/3Ba_0.01(Mg_0.5Sn_0.5)O₃ ceramics that were sintered at 1550 °C for 4 h. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical properties of trigonal single crystals (Yb,Tm)Al3(BO3)4 grown from fluxes based on the bismuth and lithium molybdates

The conditions for synthesis of Yb _x Tm_{1 − x} Al₃(BO₃)₄ (x = 0, 0.1, 0.2, 1.0) single crystals from fluxes based on bismuth trimolybdate Bi₂Mo₃O₁₂ and lithium molybdate Li₂MoO₄ are investigated. It is proposed to grow them by the group method on seeds. The polarized optical absorption spectra are measured for two mutually orthogonal linear polarizations at temperatures of 100 and 300 K.     

Growth and magnetic‐optical properties of Sr3Gd(BO3)3 and Sr3TbxGd1‐x(BO3)3 single crystals

Single crystals of Sr₃Gd(BO₃)₃ (SGB) and Sr₃Tb_xGd_1‐x(BO₃)₃ (TSGB) with dimension Ø 20 mm×20 mm have been grown by Czochralski method. The grown crystals were characterized by X‐ray powder diffraction analysis which showed the crystals belong to hexagonal structure with lattice parameters of a=b=1.254 nm, c=0.926 nm (SGB) and a=b=1.253 nm, c=0.925 nm (TSGB). In TSGB, x=17.7% was obtained by X‐ray fluorometry which showed the segregation coefficient of Tb is closed to 1. The transmission spectrum was measured, which indicated the crystals have high transmittance in 400‐1100 nm region. The Faraday rotation of single crystals at 532 nm wavelength was measured at room temperature. Finally, the Verdet constants were investigated, (SGB) V=17.9 degcm^‐1T^‐1 and (TSGB) V=21.3 degcm^‐1T^‐1. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and optical properties of self-frequency-doubling laser crystal Yb:LuAl3(BO3)4

Single crystal of Yb:LuAl₃(BO₃)₄(Yb:LuAB) was grown by the flux method for the first time. The cell parameters of the grown crystal were estimated by X-ray diffraction analysis. The result indicates the symmetry of trigonal space group R32, with lattice parameters a=b=9.26372 Å, c=7.21405 Å, V=536.14 Å³, and Z=4. The absorption and emission spectra of Yb:LuAB crystal at room temperature has also been studied. The fluorescence lifetime for Yb:LuAB crystal is about 1.48 ms. The heat capacity was measured from 25 to 500 °C. Its second harmonic generation efficiency in LuAl₃(BO₃)₄ crystal is 3–4 times that of KDP crystal. These results show that Yb:LuAB crystal would be a potential self-frequency-doubling laser crystal.     

Growth,crystal structure and spectrum of a novel rare‐earth orthophosphate crystal: Yb:LuPO4

Yb: LuPO₄ crystals with the size up to 6×2×0.5mm³ were grown by the flux growth process using lead pyrophosphate Pb₂P₂O₇ as the high‐temperature solvent. The crystal structure of Yb: LuPO₄ crystals at room temperature was refined by using single crystal X‐ray diffraction data. Crystal structure analysis showed that Yb: LuPO₄ crystals possessed the tetragonal xenotime structure. The polarized absorption spectra of Yb: LuPO₄ were tested at room temperature. The results showed that the absorption spectral region of Yb: LuPO₄ crystal was well matched for pumping with readily available diode lasers.     

Phase equilibria in the Ba2Na3[B3O6]2F-BaF2 system

The phase equilibria in the Ba₂Na₃[B₃O₆]₂F-BaF₂ section, which belongs to the ternary mutual Ba, Na//BO₂,F system, have been studied by the methods of solid-phase synthesis, visual polythermal analysis, and differential-thermal analyses. It is shown that this section can be used to grow bulk Ba₂Na₃[B₃O₆]₂F crystals.     

Laser-induced crystallization of β′-RE2(MoO4)3 ferroelectrics (RE: Sm, Gd, Dy) in glasses and their surface morphologies

The glasses with the compositions of 21.25RE₂O₃-63.75MoO₃-15B₂O₃ (RE: Sm, Gd, Dy) were prepared and the formation of β′-RE₂(MoO₄)₃ ferroelectrics was confirmed in the crystallized glasses obtained through a conventional crystallization in an electric furnace. The features of the glass structure and crystallization behavior were clarified from measurements of Raman scattering spectra. Continuous-wave Nd:YAG laser with a wavelength of 1064 nm (laser power: 0.6-0.9 W, laser scanning speed: S = 1-16 μm/s) was irradiated to 10.625Sm₂O₃-10.625Gd₂O₃ (or Dy₂O₃)-63.75MoO₃-15B₂O₃ glasses, and the structural modification was induced at the glass surface. At the scanning speed of S = 10 μm/s, crystal lines consisting of β′-Gd_2−xSm_x(MoO₄)₃ or β′-Dy_2−xSm_x(MoO₄)₃ crystals were patterned on the glass surface. It was found that those crystal lines have the surface morphology with periodic bumps. At S = 1 μm/s, it was found that crystal lines consist of the mixture of paraelectric α-Gd_2−xSm_x(MoO₄)₃ and ferroelectric β′-Gd_2−xSm_x(MoO₄)₃ crystals, indicating the phase transformation from the β′ phase to the α phase during laser irradiation. Homogeneous crystal lines with β′-RE₂(MoO₄)₃ ferroelectrics have not been written in this study, but further research is continuing.