用光谱和EPR谱确定CsMgBr3:Ni2+的局域结构

本文采用半自洽场(semi-SCF)自由Ni2 的3d轨道波函数、点电荷—偶极子模型和Ni2 -6X-(X=F,Cl,Br,I)络合物的μ-κ-α模型,建立了结构参数与光谱、EPR谱之间的定量关系,利用完全对角化方法,由光谱和电子顺磁共振(EPR)谱,确定了CsMgBr3:Ni2 晶体在77K温度时的局域结构参数,统一解释了CsMgBr3:Ni2 晶体的局域结构、光谱和EPR谱。所得理论结果与实验值符合得很好。此外,还讨论了晶体局域结构发生畸变的原因。     

Contrasting physical properties of the trilayer nickelates Nd_4Ni_3O_(10) and Nd_4Ni_3O_8

We report the crystal structures and physical properties of trilayer nickelates Nd4Ni3O10and Nd4Ni3O8.Measurements of magnetization and electrical resistivity display contrasting behaviors in the two compounds.Nd4Ni3O10shows a paramagnetic metallic behavior with a metal-to-metal phase transition(T^*)at about 162 K,as revealed by both magnetic susceptibility and resistivity.Further magnetoresistance and Hall coefficient results show a negative magnetoresistance at low temperatures and the carrier type of Nd4Ni3O10is dominated by hole-type charge carriers.The significant enhancement of Hall coefficient and resistivity below T*suggests that effective charge carrier density decreases when cooling through the transition temperature.In contrast,Nd4Ni3O8 shows an insulating behavior.In addition,this compound shows a paramagnetic behavior with the similar magnetic moment as that of Nd4Ni3O10derived from the Curie-Weiss fitting.This may suggest that the magnetic moments in both systems are contributed by Nd^3+ ions.By applying pressures up to about 49 GPa,the insulating behavior is still present and becomes even stronger under a high pressure.Our results suggest that the different Ni configurations(Ni^1+/2+ or Ni^2+/3+)and the changes of coordination environment of Ni sites may account for the contrasting behaviors in trilayer nickelates Nd4Ni3O10and Nd4Ni3O8.     

(Sr,Ca)4Si3O8Cl4基质中Eu2+的发光特性研究

采用高温固相法合成Sr4-xCaxSi3O8Cl4：Eu^2＋荧光材料,利用Van Uitert公式讨论Sr4-xCaxSi3O8Cl4：Eu^2＋中yEu^2＋的晶格环境和发光特性,确定晶体中有蓝色和黄绿色两种发光中心,并讨论了它们与光谱结构的对应关系。当0〈x〈0．5,Ca^2＋固溶入Sr4Si3O8Cl4基质晶格,Eu^2＋占据八配位Si^2＋格位,晶体主要产生蓝色中心的蓝绿色发射;当0．5〈x〈2,较大的Ca^2＋掺杂使晶胞参数变小,品格中的杂质束缚激子态的束缚增强,Eu^2＋处于杂质束缚激子中心所形成的激发态能量进一步降低,发射位于长波段方向并具有较大的Stokes位移,Sr4-xCaxSi3O8Cl4：yEu^2＋主要产生黄绿色中心的黄绿色发射光。     

Yb,Na:PbF(2): a potential new high-power laser material

Yb:PbF(2) and Yb,Na:PbF(2) laser crystals are grown by the Bridgman method. Room-temperature absorption, photoluminescence spectra, and fluorescence lifetimes of Yb(3+) ions in the crystals have been investigated. Experimental results show that Na(+) ions codoping with Yb(3+) as charge compensators can suppress the deoxidization of Yb(3+) to Yb(2+). The result of diode-pumped laser operation of a Yb,Na:PbF(2) single crystal is reported for the first time to the best of our knowledge . With a 1mol.%Yb(3+)-doped sample, we obtained 2.37W output power at 1056nm for 17.9W of incident power at 978nm.     

Variable-frequency EPR study of Mn(2+)-doped NH(4)Cl(0.9)I(0.1) single crystal at 9.6, 36, and 249.9 GHz: structural phase transition

Multifrequency electron paramagnetic resonance studies on the Mn(2+) impurity ion in a mixed single crystal NH(4)Cl(0.9)I(0.1) were carried out at 9.62 (X-band) in the range 120-295 K, at 35.87 (Q-band) at 77 and 295 K, and at 249.9 GHz (far-infrared band) at 253 K. The high-field EPR spectra at 249.9 GHz are well into the high-field limit leading to a considerable simplification of the spectra and their interpretation. Three magnetically inequivalent, but physically equivalent, Mn(2+) ions with their respective magnetic Z-axes oriented along the crystallographic [100], [010], [001] axes were observed. Simultaneous fitting of EPR line positions observed at X-, Q-, and far infra-red bands was performed using a least-squares procedure and matrix diagonalization to estimate accurately the Mn(2+) spin-Hamiltonian parameters. The temperature variation of the linewidth and peak-to-peak intensities of the EPR lines indicate the presence of lambda-transitions in the mixed NH(4)Cl(0.9)I(0.1) crystal at 242 and 228 K consistent with those observed in the pure NH(4)Cl and NH(4)I crystals, respectively. A superposition-model analysis of the spin-Hamiltonian parameters reveals that the local environment of the Mn(2+) ion is considerably reorganized to produce axially symmetric crystal fields about the respective Z-axes of the three magnetically inequivalent ions as a consequence of the vacancy created due to charge-compensation when the divalent Mn(2+) ion substitutes for a monovalent NH(4)(+) ion in the NH(4)Cl(0.9)I(0.1) crystal. This reorganization is almost the same as that observed in NH(4)Cl and NH(4)I single crystals, although the latter two are characterized by different, simple cubic and face-centered cubic, structures.     

纳米固体超强酸的制备及表征

本文采用不同的金属离子(Sn2+,Sn4+,Al3+,Ag+,Ni2+)和SO2-4浸渍ZrO(OH)2的方法制备了一系列金属改性的SO2-4/ZrO2的纳米固体超强酸。并通过指示剂法测定其酸强度,用IR、BET、XRD、TEM及化学分析等多种试验手段对催化剂进行表征,并通过正己烷裂解反应考察了该类固体超强酸催化剂的催化活性。结果发现:不同的金属离子掺杂制得的改性SO2-4/ZrO2催化剂具有不同的性能。Sn2+、Sn4+和Al3+掺杂的超强酸有较强的酸性,但只有Ni2+、Sn2+掺杂的SO2-4/ZrO2样品具有正己烷裂解反应活性,Ag+、Sn4+掺杂改性的SO2-4/ZrO2样品不具有正己烷裂解活性。     

Fast Liquid Phase Epitaxial Growth for Perovskite Single Crystals

Semiconductors grown by the solution-processed method have shown low-cost,facile fabrication process and comparable performance.However,there are many reasons why it is difficult to achieve high quality films.For example,lattice constant mismatch is one of the problems when photovoltaic devices made of organ metallic perovskites.In this work,MAPbBr^{MA=CH3NH3^+}perovskites single crystals grown on the surface of MAPbBr2.5 CI0.5 perovskites single crystals via liquid epitaxial growth method is demonstrated.It is found that when the lattice constants of the two perovskite single crystals are matched,another crystal can be grown on the surface of one crystal by epitaxial growth.The whole epitaxy growth process does not require high heating temperature and long heating time.X-ray diffraction method is used to prove the lattice plane of the substrate and the epitaxial grown layer.A scanning electron microscope is used to measure the thickness of the epitaxial layer.Compared with perovskite-based photodetectors without epitaxial growth layer,perovskite-based photodetectors with epitaxial growth layer have lower dark current density and higher optical responsibility.     

NiSO4·6H2O晶体的结构、光学和磁学性质的理论研究

采用半自洽场(semi-SCF)3d波函数、Ballhausen的自洽场(SCF)O2-波函数和点电荷模型,通过能量完全对角化方法(CDP),对NiSO4·6H2O晶体在常温下的局部对称结构、吸收光谱,电子顺磁共振谱(EPR)以及磁化率x作出了统一解释.将计算结果与实验值进行了比较.讨论了微扰方法、分子轨道方法(LCAO-MO)、参量拟合方法、Clementi单Zeta波函数等问题.     

Local spin density in the Cr(7)Ni antiferromagnetic molecular ring and (53)Cr-NMR

We present (53)Cr-NMR spectra collected at low temperature in a single crystal of the heterometallic antiferromagnetic (AF) ring Cr(7)Ni in the S?=?1/2 ground state with the aim of establishing the distribution of the local electronic moment in the ring. Due to the poor S/N we observed only one signal which is ascribed to three almost equivalent (53)Cr nuclei in the ring. The calculated spin density in Cr(7)Ni in the ground state, with the applied magnetic field both parallel and perpendicular to the plane of the ring, turns out to be AF staggered with the greatest component of the local spin ?s? for the Cr(3+) ions next to the Ni(2+) ion. The (53)Cr-NMR frequency was found to be in good agreement with the local spin density calculated theoretically by assuming a core polarization field of H(cp)?=-?11?T/μ(B) for both orientations, close to the value found previously in Cr(7)Cd. The observed orientation dependence of the local spin moments is well reproduced by the theoretical calculation and evidences the importance of single-ion and dipolar anisotropies.     

Ni2+掺杂近化学计量比铌酸锂晶体的生长及光谱特性

以K2O为助熔剂,在较大的固液界面温度梯度条件下,应用坩埚下降法技术生长了初始Ni2 掺杂摩尔分数为0.5%的近化学计量比铌酸锂晶体。测定了晶体的吸收光谱,观测到由Ni2 离子在八面体中3A2g(F)→3T1g(P)、3A2g(F)→3T1g(F)、3A2g(F)→3T2g(F)能级的正常自旋允许跃迁所产生的381 nm,733 nm,1280 nm吸收峰和3A2g(F)→1T2g(D)和3A2g(F)→1E(D)能级的自旋禁戒跃迁产生的430 nm与840 nm吸收峰。从晶体紫外吸收边的位置初步估算其摩尔分数比x(Li )/x(Nb5 )为0.981。根据晶体分裂场理论和吸收光谱,计算了Ni2 在该铌酸锂晶体中的晶格场分裂参量Dq=781 cm-1、Racah参量B=1096 cm-1与C=4353 cm-1。研究了在不同激发波长下晶体在可见光波段的荧光特征,观察到500~630 nm的绿色与800~850 nm的红色荧光发射带,它们归结为1T2g(D)→3A2g(F)与1T2g(D)→3T2g(F)的能级跃迁所致。     

Optical properties of Mg~(2+),Yb~(3+),and Ho~(3+) tri-doped LiNbO_3 crystals

A series of LiNbO_3 crystals tri-doped with Mg~(2+),Yb~(3+),and Ho~(3+) are grown by the conventional Czochraski technique.The concentrations of Mg~(2+),Yb~(3+),and Ho~(3+) ions in Mg:Yb:Ho:LiNbO_3 crystals are measured by using an inductively coupled plasma atomic emission spectrometry.The x-ray diffraction is proposed to determine the lattice constant and analyze the internal structure of the crystal.The light-induced scattering of Mg:Yb:Ho:LiNbO_3 crystal is quantitatively described via the threshold effect of incident exposure energy flux.The exposure energy(E_r) is calculated to discuss the optical damage resistance ability.The exposure energy of Mg(7 mol):Yb:Ho:LiNbO3 crystal is 709.17 J/cm~2,approximately 425 times higher than that of the Mg(l mol):Yb:Ho:LiNbO_3 crystal in magnitude.The blue,red,and very intense green bands of Mg:Yb:Ho:LiNbO_3 crystal are observed under the 980-nm laser excitation to evaluate the up-conversion emission properties.The dependence of the emission intensity on pumping power indicates that the up-conversion emission is a two-photon process.The up-conversion emission mechanism is discussed in detail.This study indicates that Mg:Yb:Ho:LiNbO_3 crystal can be applied to the fabrication of new multifunctional photoluminescence devices.     

Tracer impurity diffusion in single-crystal rutile (TiO2−x)

By means of the radioactive-tracer sectioning technique, the tracer diffusion of the impurity ions, ⁴⁶Sc, ⁵¹Cr, ⁵⁴Mn, ⁵⁹Fe, ⁶⁰Co, ⁶³Ni and ⁹⁵Zr, in rutile single crystals was measured as functions of crystal orientation, temperature, oxygen partial pressure and Al impurity content. The diffusion coefficients are very sensitive to the electric charge of the impurity ions. Divalent impurities (e.g., Co and Ni) diffuse extremely rapidly in TiO₂, compared to cation self-diffusion, and exhibit an extreme anisotropy in diffusion behavior, divalent-impurity diffusion parallel to the c-axis is much larger than it is perpendicular to the c-axis. Trivalent impurity ions (Sc and Cr) and tetravalent impurity ions (Zr) diffuse similar to cation self-diffusion, both as functions of temperature and oxygen partial pressure. The divalent impurity ions Co and Ni apparently diffuse as interstitial ions along open channels parallel to the c-axis. The results suggest that Sc, Cr and Zr ions diffuse by an interstitialcy mechanism involving the simultaneous and cooperative migration of tetravalent interstitial titanium ions and the tracer-impurity ions. Iron ions diffuse both as divalent and as trivalent ions. The impurity diffusion as functions of oxygen partial pressure and Al-impurity content are consistent with calculations of point-defect concentrations in rutile.     

ZnO对EU:LiNbO3晶体的性能及光谱性质影响

应用坩埚下降法技术，以同成份化学摩尔分数[x（Li2O）=48．6％,x（Nb2O3）=51．4％]为原料，生长出了以不同Zn，Eu双掺杂的LiNbO3晶体。测定了晶体下部与上部的X射线衍射图（XRD）、激发光谱、荧光光谱以及声子边带谱。Zn的掺杂量对Eu^3＋离子在晶体中的分布产生很大的影响。Zn掺杂摩尔分数为3％时．Eu^3＋离子在进入品格时受到有效的压制。随着Zn掺杂摩尔分数提高，达到6％时，压制作用减弱。从Zn^2＋离子在LiNbO3中随浓度变化的分凝情况以及对Eu^3＋离子的排斥作用解释了Eu^3＋离子分布的原因。同时测定了Zn掺杂样品的声子边带谱。     

掺铋BaF2晶体的制备及其近红外发光研究

通过温度梯度法制备了Bi₂O₃:BaF₂以及BiF₃:BaF₂晶体.在Bi₂O₃:BaF₂晶体中观察到了发光峰位于961 nm,半高宽202 nm的超宽带红外发光.在BiF₃:BaF₂晶体中检测到Bi²⁺和Bi³⁺可见区的发光,但是没有观察到红外发光.通过γ射线辐照实现了BiF₃:BaF₂晶体的近红外发光, 发光峰位于1135 nm,半高宽192 nm.讨论了Bi₂O₃和BiF₃掺杂BaF₂晶体的红外发光的机理. 关键词： 近红外发光 铋 氟化钡晶体 γ辐照     

Low-symmetry spin hamiltonian and crystal field tensors analysis: Fe(3+) in natrolite

Electron paramagnetic resonance study of a natural single crystal of natrolite was carried out at the frequency nu=36.772 GHz at room temperature. The angular dependence of the four symmetry-related spectra of Fe(3+) in the three crystallographic planes was fitted to a spin Hamiltonian (S=5/2) of symmetry C(i). The rank 4 crystal field tensors at tetrahedral sites were calculated using the point-charge model to determine the principal axes orientations of their cubic and trigonal components. The analysis of zero-field splitting tensors and comparison with crystal field ones suggests that Fe(3+) substitutes for Al(3+) with no significant distortion of the coordination tetrahedron in natrolite. Comparison of data for several natural and synthetic crystals reveals that the 4-rank zero-field splitting tensor invariants for Fe(3+) at the tetrahedral oxygen-coordinated sites are distinguishably smaller than those for Fe(3+) at octahedral sites. Such comparative analysis may help to determine the substitutional sites in other crystals.     

Production of high circular polarization by ion surface scattering of ferromagnets

From a theoretical analysis we predict large fractions of circular polarization of light emitted by ions scattered from surfaces of ferromagnetic single crystals. Maximum enhancement of circular polarization as compared to surface ion scattering from non-magnetic materials is again expected at grazing incidence. A circular polarization of 89% was estimated for the case of Ar⁺ ions scattered from the (110) plane of a Ni single crystal.     

两种国产新型掺Yb氟化物激光晶体的光谱特性研究

掺Yb氟化物激光材料是继掺Yb氧化物激光材料之后的另一类重要的掺Yb激光材料,已经成为可调谐激光和超快激光领域中研究的热点之一。针对两种国产新型掺Yb的氟化物激光材料：混晶材料Yb∶CaF₂-SrF₂和共掺离子型的单晶材料Yb, Y∶CaF₂,进行了详细的光谱特性比对实验研究。通过荧光比对实验,发现这两类激光材料的荧光光谱完全不同,并分析了不同荧光产生的物理机制。通过吸收率比对实验,讨论了两类材料中的激活离子Yb或共掺离子Y的掺杂浓度对晶体吸收特性的影响,得到了最佳掺Yb离子或共掺Y离子的浓度。利用激光二极管作为泵浦源,实现了这两类新型材料在折叠腔型下的连续激光输出运转,其中对于共掺离子型Yb, Y∶CaF₂晶体是首次实现连续激光运转。通过激光对比实验,获得了两类激光材料(四种样品)的激光输入—输出关系曲线,测量了各自的斜效率和激光光谱特征。通过系统地比较两类激光晶体的吸收率、荧光光谱特性、激光光谱特性以及连续激光运转的阈值功率和斜效率等参数得出以下结论：在四种实验样品中,共掺离子型单晶材料中的3at%Yb, 6at% Y∶CaF₂晶体具有最好的光谱和激光特性,具有良好的应用前景。这些实验结果为进一步提升此类激光材料的性能提供了有益的参考。     

铬、钕双掺钆镓石榴石(Cr~(4+),Nd~(3+))∶Gd_3Ga_5O_(12)激光晶体光学性能的研究

用提拉法生长了掺铬、钕的钆镓石榴石(Cr4+,Nd3+∶GGG)自调Q激光晶体。报道了室温下的吸收光谱和荧光光谱特性。分析了Cr离子浓度对光谱性质的影响。比较了Cr4+∶GGG,Nd3+∶GGG和(Cr4+,Nd3+)∶GGG晶体吸收光谱的关系。测量了(Cr4+,Nd3+)∶GGG晶体和Nd3+∶GGG晶体的荧光寿命,它们分别是33μs和250μs。实验表明,(Cr4+,Nd3+)∶GGG晶体是一种非常有潜力的自调Q激光晶体,可以实现大功率激光器的小型化和全固态化。     

Effect of 100 keV N+ ion irradiation on the organic single crystal of hippuric acid for nonlinear optical applications

The potential organic nonlinear optical material of hippuric acid (HA) single crystal has been grown by the slow evaporation solution growth technique using N, N-dimethylformamide as the solvent. Single crystals of pure HA were irradiated at room temperature with 100 keV Nitrogen (N⁺) ions at fluence 1×10¹⁶ and 5×10¹⁶ ions/cm². The pure and irradiated HA single crystals were characterized by different characterization technique. The photoluminescence and UV–visible absorption were performed at room temperature. The crystalline perfection of the pure and irradiated single crystals has been examined by high-resolution X-ray diffraction. Vickers microhardness technique was used to study the effect on the mechanical strength of the crystal at different ion fluences. The structural changes were analyzed by powder X-ray diffraction analysis. The functional groups of the synthesized compound have been identified by Fourier transform infrared spectroscopy. The dielectric constant and dielectric loss as a function of frequency were analyzed at room temperature.     

Efficient neodymium-doped glass-ceramic fiber laser and amplifier

We report an efficient glass-ceramic fiber laser and show that its slope efficiency (~30%) is not compromised by the presence of Nd-doped fluoride crystals embedded within the core of the single-mode optical fiber. In contrast, the spectroscopy (fluorescence and gain spectrum) of the Nd(3+) ions is dramatically changed by the ceramming process, an indication of strong partitioning of the rare-earth ions into the CdF(2):PbF(2):YF(3) crystal environment. The enormous potential for a new range of optical devices based on transparent glass-ceramic materials is highlighted.