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.     

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.     

Czochralski growth of Lu1‐xScxBO3:Ce solid solution crystals

Single crystals of Lu_1‐xSc_xBO₃:Ce (x=0.2, 0.3, 0.5, 0.7) were grown by Czochralski method. Continuous solid solution with calcite structure and a linear compositional dependency of crystal lattice parameter in the system Lu_1‐xSc_xBO₃:Ce are formed and their symmetry belong to hexagonal system with R3c space group checked by X‐ray powder diffraction. The electron probe micro‐analysis measurements show that the main inclusions in Lu_1‐xSc_xBO₃:Ce crystals are in the form of Sc rich oxide and Ce rich oxide. The ICP‐AES tests show that the more Sc ion content in Lu_1‐xSc_xBO₃:Ce, the smaller effective segregation coefficient of Ce in crystal will be. The X‐ray excited luminescence spectra of Lu_1‐xSc_xBO₃:Ce crystals all present a double peaked emission band with maxima round 370 and 400 nm corresponding to Ce³⁺ emission and a self trapped excitons (STE) band peaking at 269 nm. In addition, due to high density, high relative light yield, fast decay time and no‐hygroscopic property, Lu_0.8Sc_0.2BO₃:1 at%Ce crystal could be a good candidate material for scintillation application by improving the crystal quality and cerium concentration. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Laser‐induced crystal growth of nonlinear optical Ba3Ti3O6(BO3)2 on glass surface

Nonlinear optical Ba₃Ti₃O₆(BO₃)₂ crystals were patterned on the surface of CuO (1 mol%)‐doped 40BaO‐40TiO₂‐20B₂O₃ glass by irradiations of continuous‐wave Nd:YAG (wavelength: λ=1064 nm) and Yb:YVO₄ (λ=1080 nm) lasers. Laser energies absorbed by Cu²⁺ ions were transferred to the lattice system through a nonradiative relaxation process, consequently heating the glass and inducing local crystallizations. For the lines patterned by Yb:YVO₄ laser irradiations with a power of 1 W and a scanning speed of 20 μm/s, a c‐axis orientation of Ba₃Ti₃O₆(BO₃)₂ crystals along the laser scanning direction is proposed from measurements of X‐ray diffraction analyses, polarized optical photographs, polarized micro‐Raman scattering spectra, and azimuthal dependence of second harmonic generations. The laser‐induced crystallization technique is found to be applied successfully for the spatially selective patterning of nonlinear optical Ba₃Ti₃O₆(BO₃)₂ crystals in glass. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Search for compounds of the NaBaR(BO3)2 family (R = La, Nd, Gd, and Yb) and the new NaBaYb(BO3)2 orthoborate

A search for compounds of the NaBaR(BO₃)₂ composition (where R = La³⁺, Nd³⁺, Gd³⁺, or Yb³⁺) is performed by solid state synthesis and spontaneous crystallization. A new compound, NaBaYb(BO₃)₂, is found in this series. It crystallizes in space group $R\bar 3$ and belongs to the family of sublayer complex orthoborates with isolated BO₃ groups NaBaR(BO₃)₂ (R = Y, Sc, and Yb). Theoretical X-ray powder diffraction patterns of NaBaY(BO₃)₂, NaBaSc(BO₃)₂, and NaBaYb(BO₃)₂ are calculated based on single-crystal data.     

Growth and downconversion luminescence of Ho3+/Yb3+ codoped α‐NaYF4 single crystals by the Bridgman method using a KF flux

Downconversion (DC) luminescence with emission at about 1000 nm under excitation of 448‐nm light in Ho³⁺/Yb³⁺ codoped α‐NaYF₄ single crystal is realized. The crystal was grown by the Bridgman method using KF as an assisting flux in a NaF‐YF₃ system. The energy‐transfer process and quantum cutting (QC) mechanisms are presented through the analysis of the spectra. The energy‐transfer processes of first‐ and second‐order cooperative DC are responsible for the increase of the emission intensity at 1000 nm, and it is the first‐order cooperative DC that is dominant for the DC process. When the Ho³⁺ concentration is fixed at about 0.8 mol%, the optimal concentration for ∼1000 nm emission is 3.02 mol% Yb³⁺ in the current research. The energy‐transfer efficiency and the total quantum efficiency are analyzed through the luminescence decay curves. The maximum quantum cutting efficiency approaches to 184.4% in α‐NaYF₄ single crystals of 0.799 mol% Ho³⁺ and 15.15 mol% Yb³⁺. However, the emission intensity at 1000 nm decreases while the energy‐transfer efficiency from Ho³⁺ to Yb³⁺ increases, which may result from the fluorescence quenching between Ho³⁺ and Yb³⁺ ions, Yb³⁺ and Yb³⁺ ions.     

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)     

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.     

Crystal growth and spectroscopic properties of Yb:CaYAlO4 single crystal

A Yb³⁺-doped CaYAlO₄ laser crystal has been grown by the Czochralski technique. The segregation coefficient was measured by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). The cell parameters were analyzed with X-ray diffraction experiments. Color defects in Yb:CaYAlO₄ have been evidenced to be similar to those in undoped CaYAlO₄. The polarized absorption spectra and the fluorescence spectrum of the Yb:CaYAlO₄ crystal were measured at room temperature. The fluorescence decay time of the Yb³⁺ ion was investigated. The results show that Yb:CaYAlO₄ has potential as a laser gain medium for an ultrashort laser system.     

Neodymium incorporation into YAl-borate crystals in preparation from solutions in molten potassium trimolybdate

The limits of neodymium substitution for yttrium in (Y, Nd)Al₃(BO₃)₄ crystals in preparation from solutions in molten potassium trimolybdate have been studied. The maximum neodymium concentration in the crystals was 72 at.%, this corresponding to the ratio Nd:Y = 1 in the solution. When this ratio exceeds unity, only potassium-neodymium molybdate is formed. The distribution coefficient for neodymium is greater than unity and decreases both with the increasing Nd/Y ratio in the melt and with decreasing growth rate of the crystals. The unit cell parameters change in the series YAl₃(BO₃)₄ NdAl₃(BO₃)₄ in a non-steady manner, this indicating that the structure is inclined to disordering.     

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)     

Determination of Concentration of Rare Earth Ions Yb3+, Er3+, Tb3+, Ho3+, Tm3+ in Monocrystals of Yttriumaluminum Garnets on Basis of Magnetic Susceptibility

Crystals of solid solutions (R_xY_1-x)₃Al₅O₁₂ (where R is rare earth ion Er³⁺, Yb³⁺, Tb³⁺, Ho³⁺, Tm³⁺) with garnet structure were grown. The temperature dependencies of magnetic susceptibility for these crystals were obtained. On the basis of measurement of magnetic susceptibility a non-destructive technique for determining the concentration of rare earth ions in yttrium-aluminum garnets was developed.     

Structural,optical and dielectric studies on K1‐x(NH4)xH2PO4 mixed crystals grown from z‐cut seeds

Mixed crystals of K_1‐x(NH₄)_xH₂PO₄(KADP) were grown from KDP (KH₂PO₄) dominated mixed solutions with varying molar proportion of ADP (NH₄H₂PO₄) addition. It was found that, as the increase of ADP molar concentration, the growth rate along z‐axis of KADP crystal decreased rapidly. The structure of KADP crystals was investigated by powder XRD and the lattice parameter was calculated. The results showed that the lattice parameter c of KADP crystal increased with the molar concentration of ADP. The optical homogeneity of grown KADP crystals was determined with a differential phase‐shifting interferometry. Frequency dependences of the dielectric constant and dielectric loss of KADP crystals were measured at room temperature (290 K). The dielectric constants of KADP crystals were almost invariant with the increase of frequency. In the region of 10²∼10⁴Hz, the values of the dielectric loss reduced with the increase of frequency. The piezo‐resonance coupling effect still exists in KADP crystals at room temperature, but shifted to low frequency band. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Low symmetry centers in LiNbO3 doped with Yb and Er

Electron paramagnetic resonance spectroscopy studies of LiNbO₃ single crystal doped with 1 wt% of Yb³⁺ and 0.1 wt% Er are reported. Additionally, Raman spectra of the following crystals are presented: LiNbO₃:Nd, Yb (0.5 wt%, 0.7 wt%), LiNbO₃:Nd, Mg (2 wt%, 6 wt%), and LiNbO₃:Er (0.3 wt%). Raman spectra have revealed bands in the 50–220 cm^?1 range, suggesting the presence of localized phonons. The localized phonons may be considered as indirect evidence of local perturbations around Yb/Er ions, possibly due to formation of Yb/Er ion pairs. EPR spectra are interpreted basing on this presumption using a spin Hamiltonian for the Yb³⁺ dissimilar ion pairs. This model explains the observed spectral features, apparently due to the C₁ symmetry of Yb ions. In the case of the LN:Er sample, the angular dependence of EPR lines enabled distinguishing the presence of several non-equivalent centers. After deconvolution of the main EPR line into several Lorentzian components, the Er³⁺ center with the lowest C₁ point group symmetry was resolved and values of the g tensor were estimated.     

Luminescence characteristics of undoped and Eu‐doped GdCa4O(BO3)3 single crystals and nanopowders

Single crystals of GdCa₄O(BO₃)₃ (GdCOB) pure and doped with Eu concentration of 1 and 4 at% were grown by the Czochralski and micropulling‐down methods. The distribution of Eu ions in GdCOB crystals was uniform. The substitutions of Eu³⁺ in Gd, Ca(1) and Ca(2) cation sites and eventually formation Eu²⁺ have been investigated. The spectroscopic properties of crystals are compared with the properties of nanopowders obtained by sol‐gel method. Radioluminescence spectra of undoped GdCOB crystal show the characteristic emission of Gd³⁺ at about 312 nm, whereas this emission dramatically decreases in Eu‐doped crystals upon X‐ray excitation, as well as in Eu‐doped nanopowders excited in vacuum ultraviolet (VUV) region. The VUV excitation in the range 125‐333 nm for Eu‐doped samples leads to strong emission in red coming from the ⁵D₀ multiplet of Eu³⁺, only. In the photoluminescence decay kinetics of 312 nm emissions substantial shortening and departure for single exponential decay in Eu‐doped samples is clearly observed. Higher Eu doping results in further acceleration of the decay. In undoped GdCOB crystal, the lifetime of the Gd^{3+ 6}P_7/2 multiplet is 2.79 ms. The Eu^{3+ 5}D₀ decay kinetics monitored at 613 nm are rather constant. Numerical fitting of fully exponential curves, reveals lifetimes 2.7 ms for nanopowder and 2.5 ms for single crystal. The results suggest that this material may be used as a red phosphor in plasma display panels in nanopowder form because of strong excitation band of Eu³⁺ luminescence in the 160‐200 nm regions. Contrary to nanopowder sample, such an excitation band, attributed to the Gd³⁺–O^2– charge transfer was not observed in crystal obtained by the micropulling‐down method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization of PbxSr1‐x(NO3)2 Solid Solutions from Aqueous Solutions

A series of Pb_xSr_1‐x(NO₃)₂ crystals have been grown from aqueous solutions and characterized by X‐ray powder diffraction. All diffraction data were well indexed according to the simple cubic structure. The variation of lattice constants with the concentrations of Pb²⁺ in the crystals accorded quite well to the Vegard's Law. The composition of the Sr(NO₃)₂ crystal doped with Pb²⁺ was studied by electron microprobe and it was found that Pb²⁺ was enriched in the 111 sectors. Equilibrium behavior in the Pb(NO₃)₂‐Sr(NO₃)₂‐H₂O system was analyzed by Lippmann's phase diagram and the equilibrium distribution coefficient D_Pb=133.6. This large value of D indicates that Pb²⁺ ion is preferentially distributed to the solid phase.     

Mild hydrothermal synthesis and structures of mixed‐valence iron phosphates: SrFe3(PO4)3 and the interesting Mg2+‐doped AFe3 (PO4)3 (A = Ba,Pb) in Fe2+ site

Series of mixed valence monophosphates AFe_3‐xMg_x(PO₄)₃ [A = Sr(x = 0), Ba(x = 0.6), Pb(x = 0.6)] were synthesized by mild hydrothermal treatment at 210 °C. Refinements of single crystal X‐ray diffraction datas show all these compounds are isostructural. The attempts to make AFe₃(PO₄)₃ (A = Ba, Pb) hydrothermally in the experiment were unsuccessful. However, the Mg‐doped homologues AFe_2.4Mg_0.6(PO₄)₃ (A = Ba, Pb) were synthesized with the addition of MgCO₃ in the reactants as mineralizer. EDS and single crystal X‐ray data refinement indicated that the Mg²⁺ cations were doped in the Fe²⁺ sites of AFe_2.4Mg_0.6(PO₄)₃ (A = Ba, Pb). The influence of the Mg‐doping on the structure and the reason why the Mg doped in the Fe(II) site instead of A site was discussed from the point of view of the bond valence model.     

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.     

Spectroscopic properties of Yb3+ ions in halogeno-sulfide glasses

In this work, we report the optical properties of Yb³⁺ ions in halogeno-sulfide glasses of composition (75 − x)GeS₂–25Ga₂S₃–xCsCl (x = 5%, 10%, 15%, 20%, and 25% CsCl). This study includes an analysis of the influence of halide concentration on the absorption and emission cross-sections and lifetimes of Yb³⁺ ions. A blue shift of the absorption and emission bands and a decrease of the absorption and emission cross-sections and transition probability are observed as the halide concentration increases in the glass.     

Upconversion luminescence in Ho3+/Yb3+- and Tb3+/Yb3+-codoped fluorogermanate glass and glass ceramic

Energy-transfer excited upconversion luminescence in Ho³⁺/Yb³⁺- and Tb³⁺/Yb³⁺-codoped PbGeO₃–PbF₂–CdF₂ glass and glass–ceramic under infrared excitation is investigated. In Ho³⁺/Yb³⁺-codoped samples, green (545 nm), red (652 nm), and near-infrared (754 nm) upconversion emission corresponding to the ⁵S₂(⁵F₄) → ⁵I₈, ⁵F₅ → ⁵I₈, and ⁵S₂(⁵F₄) → ⁵I₇ transitions, respectively, was observed. Blue (490 nm) emission assigned to the ⁵F_2,3 → ⁵I₈ transition was also detected. In the Tb³⁺/Yb³⁺-codoped system, bright UV–visible emission around 384, 415, 438, 473–490, 545, 587, and 623 nm, identified as due to the ⁵D₃(⁵G₆) → ⁷F_J(J = 6, 5, 4) and ⁵D₄ → ⁷F_J(J = 6, 5, 4, 3) transitions, was measured. The comparison of the upconversion process in glass ceramic and its glassy precursor revealed that the former samples present much higher upconversion efficiencies. The dependence of the upconversion emission upon pump power, and doping contents was also examined. The results indicated that successive energy-transfer between ytterbium and holmium ions and cooperative energy-transfer between ytterbium and terbium ions followed by excited-state absorption are the dominant upconversion excitation mechanisms herein involved. The viability of using the samples for three-dimensional solid-state color displays is also discussed.