Thermal and laser properties of Yb:YAl3(BO3)4 crystal

Large optical-quality Yb:YAl₃(BO₃)₄(Yb:YAB) crystals have been grown by the flux method. The thermal properties of Yb:YAB crystal were measured for the first time. The thermal properties of Yb:YAB crystal with different Yb³⁺ ion concentrations are also reported. The results show that the ytterbium concentration influences the properties of Yb:YAB crystal. The specific heat decreases with the increase of Yb³⁺ ion concentrations in the experiment range. Apparently, the thermal expansion coefficient increases along the c-direction with the increase of Yb³⁺ ion concentrations, while it changes slightly along the a-direction. The output laser in 1120–1140 nm ranges has been demonstrated pumped by InGaAs laser. The slope efficiency is 3.8%. The self-frequency-doubling output power of 1 mW is achieved.     

The growth and spectroscopic characteristics of Ca3Y2(BO3)4:Er laser crystal

The Ca₃Y₂(BO₃)₄:Er³⁺ crystal with a size up to 20 mm×30 mm was grown by the Czochralski method. The absorption spectrum was measured and its absorption peaks were assigned to the corresponding transitions between the Er³⁺ energy levels. A broad emission spectrum from 1429.4 to 1662.8 nm was exhibited from 530 nm wavelength pumping. This crystal is promising as a tunable infrared laser crystal.     

Er3+单掺与Er3+/Yb3+共掺NBT-CT无铅压电陶瓷的上转换发光性能研究

采用固相烧结法制备一系列Er³⁺单掺与Er³⁺/Yb³⁺共掺0.96Na_0.5Bi_0.5TiO₃-0.04CaTiO₃(NBT-CT∶xEr³⁺/yYb³⁺,x=0.002~0.015,y=0.010)无铅压电陶瓷。通过X射线衍射仪和荧光光谱仪分别对样品的物相结构和上转换发光特性进行表征和分析。结果表明,样品的主晶相为NBT晶相。在波长为980 nm的近红外光激发下,Er³⁺单掺与Er³⁺/Yb³⁺共掺NBT-CT陶瓷均呈现强的以绿光为主的Er³⁺特征上转换发光。在NBT-CT∶xEr³⁺中,当x=0.010时上转换发光性能最佳;Yb³⁺能够起到敏化作用,明显增强Er³⁺的上转换发光强度。     

Growth and properties of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 single crystals directly from melt

Pb[(Zn_1/3Nb_2/3)_0.91Ti_0.09]O₃ (PZNT91/9) single crystals were grown by a modified Bridgman method directly from melt using an allomeric Pb[(Mg_1/3Nb_2/3)_0.69Ti_0.31]O₃ (PMNT69/31) single crystal as a seed. X-ray diffraction (XRD) measurement confirmed that the as-grown PZNT91/9 single crystals are of pure perovskite structure. Electrical properties and thermal stabilization of PZNT91/9 crystals grown directly from melt exhibit different characters from those of PZNT91/9 crystals grown from flux, although segregation and the variation of chemical composition are not seriously confirmed by X-ray fluorescence analysis (XPS). The [0 0 1]-oriented PZNT91/9 crystals cut from the middle part of the as-grown crystal boules exhibit broad dielectric-response peaks at around 105 °C, accompanied by apparent frequency dispersion. The values of piezoelectric constant d₃₃, remnant polarization P_r, and induced strain are about 1800–2200 pC/N, 38.8 μC/cm², and 0.3%, respectively, indicating that the quality of PZNT crystals grown directly from melt can be comparable to those of PZNT91/9 single crystals grown from flux. However, further work deserves attention to improve the dielectric properties of PZNT crystals grown directly from melt. Such unusual characterizations of dielectric properties of PZNT crystals grown directly from melt are considered as correlating with defects, microinhomogeneities, and polar regions.     

Floating zone growth of high-quality SrTiO3 single crystals

Strontium titanate single crystals 15–20 mm in diameter and 40–80 mm in length were grown by a floating zone method with radiation heating. Additional crystal heating just below the molten zone by an in-growth annealing furnace was applied in order to lower the temperature gradients and to achieve slower cooling of the grown crystal. The crystal perfection was studied with X-ray topography and double-crystal diffractometry. The most perfect crystals were grown in [0 0 1] direction with single grain rocking curve widths of about 30″ and subgrain misorientations of 1′–3′ over 10×10 mm² areas of the boule cross-section for both (0 0 1)-, (1 1 0)- and (1 1 1)-oriented slices. Such high-quality crystal can be grown reproducibly with starting materials of 4N grade quality.     

Flux growth of PbMg1/3Ta2/3O3 single crystals

Single crystals of PbMg_1/3Ta_2/3O₃ (PMT) were grown by the flux method. The PbO–Pb₃O₄–B₂O₃ system was used as a solvent. Transparent and light yellow PMT single crystals of rectangular shape and dimensions up to 10×6×4 mm³ were obtained. For the applied growth conditions only, the crystals of the perovskite structure were grown. X-ray diffraction tests showed that at room temperature PMT exhibits cubic symmetry with lattice parameter a=4.042(1) Å. Dielectric studies pointed to relaxor properties of PMT. The characteristic broad and frequency-dependent maximum of dielectric permittivity was observed at 179.7 K (1 kHz).     

Growth of laser single-crystals Er:YVO4 by floating zone method

High optical quality Er³⁺:YVO₄ laser crystals have been grown by using the floating zone method (FZ). The spectroscopic properties and 3 μm lasing of Er³⁺:YVO₄ were investigated. It is found that the Er³⁺ concentration has a negative effect on the emission of the transition ⁴I_13/2→⁴I_15/2(1.55 μm ), and a positive effect on that of the ⁴I_11/2→⁴I_13/2 transition (2.68 μm). With direct upper-state pumping and a plane-concave cavity a self-terminating laser was achieved at the wavelength of 2.724 μm in the 30 at% Er³⁺ doped sample.     

Growth and spectral properties of Nd-doped Sr3Y(BO3)3 crystal

A new crystal of Nd³⁺:Sr₃Y(BO₃)₃ with dimension up to 25×35 mm² was grown by Czochralski method. Absorption and emission spectra of Nd³⁺: Sr₃Y(BO₃)₃ were investigated . The absorption band at 807 nm has a FWHM of 18 nm. The absorption and emission cross sections are 2.17×10⁻²⁰ cm² at 807 nm and 1.88×10⁻¹⁹ cm² at 1060 nm, respectively. The luminescence lifetime τ_f is 73 μs at room temperature     

Crystal growth of Ce: PrF3 by micro-pulling-down method

Micro-pulling-down (μ-PD) growth apparatus was modified for fluoride crystals. PrF₃ was grown with various concentrations of Ce³⁺ from 0–100%. The crystals were transparent and colorless (CeF₃) or greenish and 3 mm in diameter and 15–50 mm in length. Neither visible inclusions nor cracks were observed. Radioluminescence spectra and decay kinetics were measured for the sample set at room temperature. In comparison to the Czochralski or Bridgman method, the μ-PD method allows to produce single crystalline material in a faster thus more economic way. Once it is established for the fluoride crystals, it is an efficient tool for exploring the field of new functional fluorides.     

Growth of pure and RE-doped Y2O3 single crystals by LHPG technique

High-quality and crack-free Y₂O₃ single crystals containing low concentrations of Tm³⁺, Tb³⁺ and Yb³⁺ were obtained. The crystals were grown in the form of monocrystalline fibers by using a floating zone method with laser heating (laser-heated pedestal growth).     

Distribution of oxidation states of Cr ions in Ca or Ca/Mg co-doped Cr:Y3Al5O12 single-crystal fibers with nitrogen or oxygen annealing environments

The valence states of Cr ions in Ca or Ca/Mg co-doped Cr:Y₃Al₅O₁₂ (YAG) single-crystal fibers are studied. The fibers were grown using the laser-heated pedestal growth method, followed by annealing treatments up to 1500 °C. The concentrations of the Cr³⁺ and Cr⁴⁺ ions in octahedral and tetrahedral sites in oxygen or nitrogen environments were characterized. Above 700 °C, migration of Cr⁴⁺ between octahedral and tetrahedral sites takes place; its relative stabilization energy was estimated. For Ca,Cr:YAG annealed in an oxygen or nitrogen environment, it was 0.25 and 0.3 eV, respectively. For Mg,Ca,Cr:YAG annealed in oxygen or nitrogen, it was 0.47 and 0.49 eV, respectively. For the Ca,Cr:YAG crystal fiber (Ca/Cr=113.1%) with oxygen annealing, about 35% and 2.5% of Ca ions took part in charge compensation for Cr⁴⁺ in the octahedral and tetrahedral sites, respectively. The density of oxygen vacancies depends on the concentration of Ca ions. The estimated ratios of the unreacted oxygen vacancies to total oxygen vacancies were about 63% and 88% for oxygen and nitrogen annealing, respectively. The main limitation on the concentration of Cr⁴⁺ in the tetrahedral site of YAG is the presence of unreacted oxygen vacancies.     

Growth and characterization of a new nonlinear optical material: Potassium p-nitrophenolate dihydrate (NO2–C6H4–OK·2H2O) with new bonding properties

Single crystals of potassium p-nitrophenolate dihydrate (NPK·2H₂O) have been grown successfully using the isothermal solvent evaporation technique. It is a new semiorganic nonlinear optical crystal, possessing a d_eff of about 1.5 times that of lithium niobate and in which the K⁺ ions are bonded to the nitro group instead of bonding with the phenolic O⁻. Large single crystals of dimension upto 20×6×4 mm³ are harvested within a period of 60 days. The grown crystals are subjected to single crystal X-ray, FTIR and DRS-UV visible spectral, thermal and microhardness analyses. Single crystal X-ray analysis confirms the molecular formula and the structure of the crystal. FTIR spectral studies verify the functional groups present in the crystal. The DRS-UV visible spectrum proved the optical transparency of the crystal in the entire visible and near infrared region. Thermal studies reveal that the crystals are stable upto 180 °C. Microhardness measurements on the cleaved plane (1 1 0) explain the strength and slip direction in the crystal. The SHG efficiency of the crystal is examined by performing the Kurtz powder test using Nd:YAG laser.     

Si4+共掺杂Yb∶YAG单晶生长和光谱特性研究

利用提拉法生长了Si⁴⁺共掺杂Yb∶YAG单晶,该晶体属于立方晶系,O_h¹⁰-Ia3d空间群。掺杂的Si⁴⁺没有改变YAG的晶体结构,但是影响了发光离子的价态。吸收光谱表明Si⁴⁺的引入使得Yb²⁺含量增多,这是由于Si⁴⁺引入了过量的电荷,为满足电价平衡,Yb³⁺转换为Yb²⁺。Yb²⁺的出现降低了Yb∶YAG的发光强度。稳态X射线激发发射光谱结果表明Si⁴⁺共掺杂Yb∶YAG晶体的发光强度是Yb∶YAG的63%,γ射线激发下的光产额降至原来的40%。此外,由于原料中含有多种Yb的同位素,Yb∶YAG除了可以被X射线、γ射线激发出荧光外,还可以与中子发生核反应产生带电粒子,进而引起次级反应产生荧光。荧光的产生仍然由Yb³⁺决定,因此,Si⁴⁺掺入也降低了中子探测灵敏度。     

Improved growth of PbI2 single crystals

The phase equilibrium and the crystallization process of lead iodide (PbI₂) melt have been primarily investigated according to the lead–iodine phase diagram. It is found that the iodine evaporation and the segregated lead deposition are the two important factors that affect the PbI₂ crystal quality. The new method of Pulling U-type quartz growth ampoule has been made to impede the decomposition of PbI₂ and the vaporization and condensation of iodine. An orange and translucent PbI₂ single crystal of large size was obtained by the improved growth method, i.e. U-type ampoule pulling. Resistivity of the as-grown crystal is up to 4×10¹¹ Ω cm, and IR transmission is up to 45% in the region from 7800 to 450 cm⁻¹. Therefore, the improved growth method is a promising convenient new method for the growth of high quality PbI₂ crystals.     

Ambient-condition growth of superconducting YBa2Cu4O8 single crystals using KOH flux

YBa₂Cu₄O₈ is a stoichiometric oxide superconductor of T_c80 K. Unlike YBa₂Cu₃O_7−δ, this compound is free from oxygen vacancy or twin formation and does not have any microscopic disorder in the crystal. Doping with Ca raises its T_c to 90 K. The compound is a promising superconductor for technological application. Up to now, single crystals have not been grown without using specialized apparatus with extremely high oxygen pressure up to 3000 bar and at over 1100 °C due to the limited range of reaction kinetics of the compound. This fact has delayed the progress in the study of its physical properties and potential applications. We present here a simple growth method using KOH as flux that acts effectively for obtaining high-quality single crystals in air/oxygen at the temperature as low as 550 °C. As-grown crystals can readily be separated from the flux and exhibit a perfect orthorhombic morphology with sizes up to 0.7×0.4×0.2 mm³. Our results are reproducible and suggest that the crystals can be grown using a conventional flux method under ambient condition.     

Flux growth of BPO4 crystals

Single crystals of BPO₄ with sizes up to 15×10×12 mm³ were grown by top-seeded solution growth method using Li₂O–Li₄P₂O₇ as fluxes. The components volatilized from the melt were characterized by the method of X-ray powder diffraction. The defects of grown crystals have also been investigated. The measured ultraviolet cutoff edge of BPO₄ was about 130 nm. Its density was 2.82 g/cm³ determined using drainage method.     

Influence of cooling rate on the liquid-phase epitaxial growth of Zn3P2

We report the liquid-phase epitaxial growth of Zn₃P₂ on InP (1 0 0) substrates by conventional horizontal sliding boat system using 100% In solvent. Different cooling rates of 0.2–1.0 °C/min have been adopted and the influence of supercooling on the properties of the grown epilayers is analyzed. The crystal structure and quality of the grown epilayers have been studied by X-ray diffraction and high-resolution X-ray rocking measurements, which revealed a good lattice matching between the epilayers and the substrate. The supercooling-induced morphologies and composition of the epilayers were studied by scanning electron microscopy and energy dispersive X-ray analysis. The growth rate has been calculated and found that there exists a linear dependence between the growth rate and the cooling rate. Hall measurements showed that the grown layers are unintentionally doped p-type with a carrier mobility as high as 450 cm²/V s and a carrier concentration of 2.81×10¹⁸ cm⁻³ for the layers grown from 6 °C supercooled melt from the cooling rate of 0.4 °C/min.     

Environmental SEM investigation on surface defects in 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 single crystal

In this paper, the technique of environmental scanning electron microscopy (ESEM) has been employed to investigate the surface defects of the (1 1 1) appearing face in 0.92Pb(Zn_1/3Nb_2/3)O₃–0.08PbTiO₃ (PZN–8%PT) crystals. From the ESEM images, we succeeded in observing and studying the growth hillocks and etch pits, low-angle grain boundaries, and sub-grain boundaries in (1 1 1) face, which were related to the generation of dislocation and stacking faults, respectively. On the other hand, an image of a unique multi-layer lamellar structure and fine step structure obtained in the (1 1 1) face reveals that the dominant fast growth mechanism of PZN–8%PT crystal grown by the flux method is a sub-step mechanism, unlike the screw dislocation growth mechanism.     

Large-size β-Ga2O3 single crystals and wafers

Large-size single crystals of β-Ga₂O₃ with 1 inc in diameter have been grown by the floating zone technique. The stable growth conditions have been determined by the examination of the crystal structure. Wafers have been cut and fine polished in the (1 0 0), (0 1 0) and (0 0 1) planes. These were highly transparent in the visible and near UV, as well as electrically conductive, indicating the potential use of β-Ga₂O₃ as a substrate for optoelectic devices operating in the visible/near UV and with vertical current flow.     

Growth of NaBi(WO4)2 crystal by modified-Bridgman method

NaBi(WO₄)₂ (NBW) crystals have been grown for the first time by modified-Bridgman method. Influences of some factors on the crystal growth process are discussed. X-ray powder diffraction experiments show that the unit cell parameters of NBW crystal are a=b=0.5284 nm, c=1.1517 nm, and V=0.3215 nm³. The differential thermal analysis shows that the NBW crystal melts at 923°C.