Optical Floating Zone Method Research Articles

Preparation and optical properties of samaria‐doped yttria‐stabilized zirconia single crystals

AbstractSingle crystals of yttria‐stabilized zirconia (YSZ) doped with various concentrations of Sm2O3 were synthesized by the optical floating zone method, and their structure and spectroscopic properties characterized using powder X‐ray diffraction (XRD), optical absorption, and luminescence measurements. XRD showed that the cubic phase of ZrO2 was stabilized by addition of Y2O3 and a series of absorption peaks characteristic of Sm3+ was detected by UV‐visible absorption spectroscopy. Three phenomenological J‐O oscillator strength parameters Ωt (t = 2, 4, 6) were calculated to evaluate the local structure and bonding in the vicinity of the Sm3+ for the 0.75 mol% Sm2O3: YSZ sample. These were in order of Ω2 < Ω4 < Ω6 with values of Ω2 = 5.46 × 10−20 cm2, Ω4 = 10.70 × 10−20 cm2, and Ω6 = 12.67 × 10−20 cm2, and indicate a relatively high symmetry and low covalent character for the Sm‐O bond at the Sm3+ sites in the YSZ matrix. Photoluminescence spectra recorded under an excitation of 404 nm showed four emission bands centered at 571 nm, 621 nm, 652 nm, and 716 nm corresponding to the transitions 4G5/2→6Hj (j = 5/2, 7/2, 9/2, 11/2). The transition probability, lifetime, and branching ratio obtained from the emission spectrum of the 0.75 mol% Sm2O3: YSZ crystal showed that YSZ is a potential host for Sm3+ to achieve a reddish‐orange laser output, and the Sm3+‐modified YSZ crystals have a possible use in reddish‐orange laser and lighting devices.

Microstructure evolution and crystallography of directionally solidified Al2O3/Y3Al5O12 eutectic ceramics prepared by the modified Bridgman method

Large size, high-density (99.97%) and well-organized Al2O3/Y3Al5O12 (YAG) eutectic ceramics were prepared by the modified Bridgman method. The evolution of the three dimensional microstructure and micropores were investigated. The diameter of the micro-pores and the porosity decreased during directional solidification. The average equivalent diameter of the micro-pores was 2.41 μm in the well-prepared eutectic ceramics. Most of the pores (98.07%) were smaller than 4 μm. These data are comparable to those prepared by the optical floating zone method. The as-grown eutectic ceramics were polycrystalline, but the interfaces were well-bonded and there were no amorphous phases in the microstructure. The misfits of the different crystallographic relationships were calculated, and the bottleneck of the single-crystal preparation was identified. These results could provide theoretical guidance for the preparation of large, single-crystal Al2O3/YAG eutectic ceramics by the modified Bridgman method.

Growth and optical properties of thulia-doped cubic yttria stabilized zirconia single crystals

Abstract Single crystals of yttria stabilized zirconia (YSZ) doped with different thulia (Tm2O3) contents (0.2–3.0 mol%) (abbreviated to Tm2O3: YSZ) were grown by the optical floating zone method. The crystals were transparent and inclusion free. These samples were then analyzed by X-ray diffraction (XRD), thermogravimetric-differential thermal analysis (TG-DSC), and Raman spectroscopy, and their optical properties were determined with Ultraviolet–visible (UV–Vis) and Photoluminescence spectroscopy (PL). The Tm2O3: YSZ single crystals were in the cubic phase, and the lattice parameters first increased and then decreased with increasing Tm2O3 content. The absorption spectra showed four peaks at around 356 nm (3H6→1D2), 460.5 nm (3H6→1G4), 678.5 nm (3H6→3F2,3) and 784 nm (3H6→3H4) in the visible region, and the optical bandgap energy increased with increasing Tm2O3 content, as a result of the Moss-Burstein effect. Measurements of PL spectra indicated a strong blue emission peak at 458 nm (1D2→3F4), and three weak emission peaks at 487 nm (1G4→3H6), 497 nm (1D2→3H5), and 656.5 nm (1G4→3F4) when the crystals were excited by light with a wavelength of 356 nm. The intensities of the emission peaks were strongly affected by the Tm2O3 content of the YSZ single crystals; the intensity increased with Tm2O3 content at low doping levels, reached the maximum at 0.5 mol% Tm2O3, then decreased with further increase in Tm2O3 content due to the concentration quenching effect. Additionally, the color changed from blue to cyan as the Tm2O3 content was increased. Overall, this work demonstrates that the cubic YSZ single crystal is a suitable host material for solid state luminescence.

Spectroscopic properties and Judd-Ofelt analysis of Nd doped GdVO4 single crystals grown by OFZ method

GdVO4 single crystals doped with different concentration of Nd (0.6, 0.8, 1.0 and 1.2 at.%) were grown by optical floating zone method. The absorption coefficient measured for two orthogonal polarization of light is different due to anisotropic structure in both the direction. The line strength and Judd-Ofelt parameters evaluated from the recorded absorption spectra are also dependent on the polarization of the incident light. Further, the spectroscopic quality factor was estimated by Judd Ofelt parameters and found to be maximum for 0.8 at.% Nd doped GdVO4 crystals. The emission study shows that photoluminescence (PL) intensity at 1062 (lasing wavelength), 1069 and 1081 nm increases with the doping concentration of Nd up to 0.8 at.% and beyond that the PL intensity at all emission wavelengths decreases. The emission cross-section with excitation at 808 nm was estimated by Judd Ofelt theory for the 4F3/2 → 4I11/2 transition and it was found to be independent of doping of Nd in GdVO4. The measured fluorescence life-time of Nd:GdVO4 samples is ∼100, 101, 92 and 93 μs corresponding to the doping concentration of 0.6, 0.8, 1.0 and 1.2 at.% of Nd respectively. The measured fluorescence life-time exhibits the maximum value for 0.8 at.% of Nd doping. The decrease in the PL intensity as well as fluorescence life-time for higher doping concentration is because of quenching due to ion-to-ion interaction in the crystal. All the spectroscopic investigation presented here suggest that the optimum concentration of Nd ion in GdVO4 single crystals is 0.8 at.%, at which the best lasing performance can be obtained.

Anomalous effect of growth ambience on the optical absorption characteristics of Cr-co-doped Nd:YVO4 crystal

Single crystals of Cr-co-doped 0.7 at.% Nd:YVO4 were grown using the optical floating zone method with varied Cr doping concentrations (0.7, 1.0, 1.4 and 2.0 at.%) in different oxygen partial pressures. The lattice parameters are unaffected by Cr doping. Further, the effect of the doping concentration and the growth atmosphere on the optical absorption, particularly for the 2A1→2B2 transition, which is due to the pentavalent state of Cr ion, has been investigated under two orthogonally polarized lights (i.e., E ⊥ [001]) and E ǁ [001]). This transition is important as it results in saturable absorption that is used for self-Q-switching of laser output. The observation suggests that the concentration of the desired pentavalent Cr increases to 1.4 and 2.0 at.% Cr as the oxygen partial pressure in the growth ambience increases, whereas for 0.7 and 1.0 at.% of Cr, the increase in the oxygen partial pressure results in an adverse effect. This finding suggests that on the basis of the concentration of Cr5+ required in Nd:YVO4 to attain the desired level of saturable absorption, the growth ambience should be chosen judiciously so that it is in line with the result presented here.

Crystal Growth of Quantum Magnets in the Rare-Earth Pyrosilicate Family R2Si2O7 (R = Yb, Er) Using the Optical Floating Zone Method

We report on the crystal growth of rare-earth pyrosilicates, R 2Si 2O 7 for R = Yb and Er using the optical floating zone method. The grown crystals comprise members from the family of pyrosilicates where the rare-earth atoms form a distorted honeycomb lattice. C-Yb 2Si 2O 7 is a quantum dimer magnet with field-induced long range magnetic order, while D-Er 2Si 2O 7 is an Ising-type antiferromagnet. Both growths resulted in multi-crystal boules, with cracks forming between the different crystal orientations. The Yb 2Si 2O 7 crystals form the C-type rare-earth pyrosilicate structure with space group C 2 / m and are colorless and transparent or milky white, whereas the Er-variant is D-type, P 2 1 / b , and has a pink hue originating from Er 3 +. The crystal structures of the grown single crystals were confirmed through a Rietveld analysis of the powder X-ray diffraction patterns from pulverized crystals. The specific heat of both C-Yb 2Si 2O 7 and D-Er 2Si 2O 7 measured down to 50 mK indicated a phase transition at T N ≈ 1.8 K for D-Er 2Si 2O 7 and a broad Schottky-type feature with a sharp anomaly at 250 mK in an applied magnetic field of 0.8T along the c-axis in the case of C-Yb 2Si 2O 7 .

Luminescence and EPR properties of high quality ruby crystals prepared by the optical floating zone method

Rubies (Cr: Al2O3 single crystals) with 0.025–0.4 mol% Cr2O3 were prepared by the optical floating zone method, and characterized by X-ray diffraction (XRD), electron paramagnetic resonance (EPR) spectroscopy, optical transmission and photoluminescence (PL). Crystals were free of inclusions and cracks, and had high transmittance in the visible region. In addition to the well-known signals from Cr3+ in the α-Al2O3 structure, the EPR spectra indicated the presence of very weak signals, which may correspond to paramagnetic centres associated with an oxygen vacancy, and an electron-loss oxygen centre, O−. The concentration of these paramagnetic centres was at a minimum for Cr2O3 concentration of 0.15 mol%, and additional Cr3+-derived peaks were also observed with Cr2O3 concentrations >0.15 mol%. The PL spectra also varied with Cr2O3 concentrations; the emission intensities of the PL spectra increased with Cr2O3 concentration for concentrations ≤0.15 mol%, then decreased with the further increases in Cr2O3. Thus the maximum luminescence emission intensity and the minimum concentration of paramagnetic structural defects were observed with 0.15 mol % Cr2O3, and the presence of additional interactions involving Cr3+ ions may contribute to the partial quenching of the luminescence at higher Cr3+ concentrations. Overall, the optical floating zone method represents an effective and economic approach to the preparation of high quality rubies, and their optimum optical properties were observed with Cr2O3 concentrations of 0.15 mol%.

High-pressure optical floating-zone growth of Li2FeSiO4 single crystals

We report the growth of mm-sized Pmnb-Li2FeSiO4 single crystals by means of the optical floating-zone method at high argon pressure and describe the conditions required for a stable growth process. The crystal structure is determined and refined by single-crystal X-ray diffraction. The lattice constants amount to a = 6.27837(3) Å, b = 10.62901(6) Å and c = 5.03099(3) Å at 100 K. In addition, we present high-resolution neutron powder diffraction data that suggest that the slight Li – Fe site exchange seems to be intrinsic to this material. High quality of the crystal is confirmed by very sharp anomalies in the static magnetic susceptibility and in the specific heat associated with the onset of long-range antiferromagnetic order at TN = 17.0(5) K and pronounced magnetic anisotropy for the three crystallographic axes. Furthermore, magnetic susceptibility excludes the presence of sizable amounts of magnetic impurity phases.

Highly efficient up-conversion green emission in Ho/Yb co-doped yttria-stabilized zirconia single crystals

In the development of materials with valuable luminescence properties, we have used the optical floating zone method to prepare single crystals in the cubic phase of yttria-stabilized zirconia (YSZ) doped with 0.75 mol% Ho2O3 and various concentrations of Yb2O3. The influence of Yb3+ contents was determined for absorption and photoluminescence spectra, and fluorescence decay curves at room temperature. The absorption spectra consisted of several peaks that could be assigned to various transitions involving Yb3+ and Ho3+ ions, and oscillator strength parameters Ωt (t = 2, 4, 6) were determined using the Judd-Ofelt theory, along with the transition probability, lifetime, and branching ratio from the absorption and emission spectra of the crystal of YSZ co-doped with 0.75 mol% Ho2O3 and 1.5 mol% Yb2O3. The Ω2 value of ~14 × 10–20 cm2 indicates that the bonding around Ho3+ involves lower symmetry and higher covalency than in several other hosts, and the value of the ratio Ω4/Ω6 of 1.93 shows that this sample is a good candidate material for high quality laser output. Up-conversion emission spectra showed that Yb3+ doping significantly increased the emission intensity of 0.75 mol% Ho2O3 doped YSZ at green (557 nm), red (670 nm) and NIR (758 nm) wavelengths when excited by a 980 nm laser, and reached a maximum for 1.5 mol% Yb2O3. The emission at 557 nm was much sharper than that reported for nanocrystals of similar composition, where the maximum intensity was observed at 540 nm. Down-conversion PL spectra showed two prominent emission peaks at 1040 nm and 1213 nm, and the fluorescence decay curves indicate that energy transfer between Yb3+ and Ho3+ influenced the lifetime of the excited state of Ho3+ which varied with Yb2O3 concentration. Overall these results indicate that these Yb/Ho co-doped YSZ crystals have considerable potential for laser and luminescence applications.

Correlation of afterglow, trap states and site preference in RE2O3:1%Eu (RE = Lu, Y, Sc) single crystal scintillators

RE2O3:1%Eu (RE=Lu, Y, Sc) single crystals were grown by the optical floating zone method. Correlated measurements of afterglow curves, thermoluminescence, photoluminescence decay, and radioluminescence curves were performed. It is found that the afterglow intensity of Sc2O3:Eu is much lower than the other two compounds and Y2O3:Eu presents a slightly lower afterglow intensity than Lu2O3:Eu. It is discussed in the light of the influence of trap states and site preference in the RE2O3:Eu. The afterglow difference between Sc2O3:Eu and other two compounds mainly comes from the disappearance of Schottky defect in Sc2O3:Eu. Meanwhile the afterglow difference between Y2O3:Eu and Lu2O3:Eu probably ascribes to the lower S6 site ratio in Y2O3:Eu. Their photoluminescence and other radioluminescence properties were also measured and compared.

Growth and properties of spinel structure Zn1.8Co0.2TiO4 single crystals by the optical floating zone method.

The spinel structure Zn1.8Co0.2TiO4 single crystals with 5 mm diameter and 30 mm length were successfully grown by an optical floating zone method. The as-grown crystals were characterized by X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS). Some Zn2+ ions at tetrahedral and octahedral sites should be replaced by doped transition metal Co2+ ions. The temperature-dependent Raman spectra of spinel Zn1.8Co0.2TiO4 crystals were also described. The optical phonon behaviors of Zn1.8Co0.2TiO4 are stable within the temperature range. The magnetic properties of Zn1.8Co0.2TiO4 were investigated by using Physical Property Measurement System.

The Raman scattering of trirutile structure MgTa2O6 single crystals grown by the optical floating zone method.

Single crystals of the trirutile structure MgTa2O6 were grown via an optical floating zone method in an air atmosphere. The as-grown crystals were pale yellow and transparent and the natural cleavage plane formed during the crystal growth was determined by XRD2 to be along the c-axis direction. The variations in valence were investigated by XPS (X-ray photoelectron spectroscopy). The room-temperature axis-relative polarized Raman spectra of trirutile MgTa2O6 crystals were described. The order–disorder effect was detected via temperature-dependent Raman spectroscopy.

Single crystal growth of bulk InGaZnO4 and analysis of its intrinsic transport properties

Large, high-quality InGaZnO4 single crystals grown by high-pressure optical floating zone method and its electrical and optical properties.

Preparation and optical properties of Ho3+-doped YSZ single crystals

Single crystals of yttria-stabilized zirconia (YSZ) doped with different contents of holmium were prepared by the optical floating zone method, and their structures and phase composition were characterized by XRD and Raman spectroscopy. These showed that the metastable tetragonal phase was stabilized by the substitutions. Transmittance of each of the Ho3+-doped YSZ single crystals was larger than 85% in the visible region. Measurements of fluorescence spectra indicated a strong emission at a wavelength of 553.5 nm, and two weak emission peaks at 671 nm and 759 nm when the crystals were excited by light with a wavelength of 448 nm. The YSZ doped with 0.75 mol% of Ho2O3 had a relatively higher fluorescence intensity and possessed high color purity (99.7%) in the green region, indicating that it can be used to produce efficient green emission.

The luminescent properties comparison of RE2O3:Eu(RE=Lu,Y,Sc) with high and low Eu doping concentrations

Single crystal scintillators of RE2O3:Eu (RE = Lu, Y, Sc) with high (8%) and low (1%) Eu doping concentration were grown by the optical floating zone method. The luminescence and scintillation properties have been investigated and compared thoroughly. Correlated measurements of afterglow curves, photoluminescence excitation and photoluminescence, photoluminescence decay curves and X-ray excitation curves were performed. Lu2O3:Eu and Y2O3:Eu present significant afterglow intensity decreasing after high Eu concentration doping. While for the Sc2O3:Eu, its afterglow intensity even increases slightly. The luminescence efficiencies of high doping concentration samples are weaker than that of the low concentration ones due to the concentration quenching. The integrated X-ray excitation luminescence reveals the scintillation luminescence efficiencies of samples with the high concentration or the low ones both have the following sequence:Lu2O3:Eu＞Y2O3:Eu＞Sc2O3:Eu.

Application of Optical Floating Zone Method to Dissolution Kinetics of Inclusions in a Steelmaking Slag

Application of Optical Floating Zone Method to Dissolution Kinetics of Inclusions in a Steelmaking Slag

Enhancing the magnetoelectric coupling of Co4Nb2O9[100] by substituting Mg for Co

We report experimental studies on enhancing the magnetoelectric (ME) coupling of Co4Nb2O9 by substituting the non-magnetic metal Mg for Co. A series of single crystal Co4–xMgxNb2O9 (x = 0, 1, 2, 3) with a single-phase corundum-type structure are synthesized using the optical floating zone method, and the good quality and crystallographic orientations of the synthesized samples are confirmed by the Laue spots and sharp XRD peaks. Although the Neel temperatures (TN) of the Mg substituted crystals decrease slightly from 27 K for pure Co4Nb2O9 to 19 K and 11 K for Co3MgNb2O9 and Co2Mg2Nb2O9, respectively, the ME coupling is doubly enhanced by Mg substitution when x = 1. The ME coefficient αME of Co3MgNb2O9 required for the magnetic field (electric field) control of electric polarization (magnetization) is measured to be 12.8 ps/m (13.7 ps/m). These results indicate that the Mg substituted Co4–xMgxNb2O9 (x = 1) could serve as a potential candidate material for applications in future logic spintronics and logic devices.

Optical properties, magnetooptical properties and terahertz time-domain spectrum of Tb3Sc2Al3O12 crystals grown by optical floating zone methods

Tb3Sc2Al3O12 crystals have been grown by optical floating zone methods for the first time. The XRD patterns of TSAG crystals match well with the standard cards and the full width half maximum of the analyzed peaks is 0.00832°. The unique emission properties of TSAG crystals have been demonstrated in detail. The Verdet constant of TSAG crystals in the whole region is nearly 20% higher than that of commercial TGG crystals. The terahertz time domain spectrum of TSAG crystals has been analyzed for the first time, and we find that the refractive index is nearly 2, and the absorption coefficient is 2/cm from 1THz to 5 THz.

Optimization of single crystal growth of candidate quantum spin-ice [formula omitted] by optical floating-zone method

We report the optimized conditions for growing the high quality single crystals of candidate quantum spin-ice Pr2Hf2O7 using the optical floating-zone method. Large single crystals of Pr2Hf2O7 have been grown under different growth conditions using a four-mirror type optical floating-zone furnace and their microscopic structural differences have been probed by high-resolution synchrotron X-ray diffraction (SXRD). The SXRD data reveal that the crystals grown under flowing argon (∼2 L/h) atmosphere with slightly off-stoichiometric (optimized) starting composition yields the highest quality crystals. The magnetic susceptibility, isothermal magnetization and heat capacity data of optimally grown crystals are presented.

Growth and Dielectric Properties of Ta-Doped La2Ti2O7 Single Crystals

High-quality Ta-doped La2Ti2O7 (Ta-LTO) single crystal of about 40 mm in length and 5 mm in diameter was successfully prepared by the optical floating zone method. An X-ray rocking curve reveals that the crystal of LTO has excellent crystalline quality. As-grown crystals were transparent after annealing in air and the transmittance is up to 76% in the visible and near-infrared region. X-ray diffraction showed that this compound possessed a monoclinic structure with P21 space group. The dielectric properties were investigated as functions of temperature (0~300 °C) and frequency (102 Hz~105 Hz). Dielectric spectra indicated an increase in the room-temperature dielectric constant accompanied by a drop in the loss tangent as a result of the Ta doping. One relaxation was observed in the spectra of electric modulus, which was ascribed to be related to the oxygen vacancy. The dielectric relaxation with activation energy of 1.16 eV is found to be the polaron hopping caused by the oxygen vacancies.