燃烧法合成Ln2O2 S:RE3+(Ln=Gd,La;RE=Eu,Tb) X射线荧光粉及发光性能

采用燃烧合成法,以稀土硝酸盐和二硫代乙二酰胺为反应物,通过控制两者的摩尔比例,在点燃温度为300—350℃时,制备了掺杂不同浓度稀土激活剂离子的硫氧化物X射线荧光粉。分别以X射线衍射(XRD)、扫描电子显微镜(SEM)、光致发光(PL)光谱及X射线激发的发光(XEL)光谱对样品进行了表征。XRD分析表明,当热处理温度低于500℃时,可得到单一相的硫氧化物X射线荧光粉,这就避免了高温烧结的缺点;而当烧结温度较高时,开始有硫酸氧化物出现。从SEM图像中可以看到荧光粉粉末具有疏松和多孔连续的三维的网络块状结构,但其初级粒子尺寸较小,均小于50nm,这在一定程度上,可以提高成像系统的空间分辨率。PL光谱分析表明,所制备的荧光粉样品分别呈现出Eu^3 ,Tb^3 离子的特征发射。XEL光谱结果表明,尽管它与光致发光的激发原理不一样,但同样呈现出Eu^3 ,TB^3 离子的特征发射;这些样品本身对X射线的吸收系数及掺杂浓度不一样,因此它们的光发射效率也有所差别。     

Thermo-optical properties of uniaxial NaT(XO4)2 laser host crystals (where T = Y, La, Gd or Bi, and X = W or Mo)

Thermo-optic coefficients dn _o/dT and dn _e/dT were measured in tetragonal double tungstate and double molybdate crystals NaT(XO₄)₂ (where T = Y, La, Gd or Bi and X = W or Mo) by a laser beam deviation method in the spectral range 0.4–1.1 μm. Thermal expansion coefficients in the directions of a and c crystallographic axes were also measured. Analytical expressions for thermo-optic dispersion formulas were derived as series in 1/λ ². All dn/dT values for NaT(XO₄)₂ crystals were found to be negative. Their absolute values satisfy the relation |dn _e/dT| > |dn _o/dT| for crystals without Bi and |dn _o/dT| > |dn _e/dT| for crystals with Bi. A clear tendency for dn/dT values to decrease with the increase of the volumetric thermal expansion coefficient α _vol of the crystal was observed. This is related with dominant contribution of volumetric thermal expansion effect to the temperature dependence of the refractive index. Thermal coefficients of the optical path W = dn/dT + (n ? 1)α _T governing thermal lensing effect were calculated for different light propagation directions and polarizations as well as crystal athermal directions.     

Initial suppression of Tc in optimally-doped Bi2Sr1.6RE0.4Cu1−xZnxO6+δ (RE = La,Pr, Nd,Sm, and Eu)

We have investigated the initial suppression of the superconducting transition temperature, T_c, by Zn substitution in Bi₂Sr_1.6RE_0.4CuO_6+δ (Bi(RE)-2201) with a single CuO₂ plane. We propose a phase diagram of Bi(RE)-2201 as a function of the degree of disorder outside the CuO₂ plane. Upon increasing the degree of disorder, while T_c decreased gradually, the pseudogap is significantly strengthened as a quadratic function of the degree of disorder. The initial suppression rate of T_c is well described by considering the enhancement of the pseudogap by the out-of-plane disorder.     

Half-metallic behavior of Co2YZ (Y = V,Cr; Z = Al,Ga) under pressure: a DFT study

The structural, electronic and magnetic properties of Co-based Heusler compounds Co₂YZ (Y = V, Cr; Z = Al, Ga) under pressure are studied using first principles density functional theory. The calculations are performed within generalized gradient approximation. The total magnetic moment decreases slightly on compression. Under application of external pressure, the valence band and conduction band are shifted downward which leads to the modification of electronic structure. There exists an indirect band gap along Г–X for all the alloys studied. Co₂CrAl shows half-metallic nature up to 85 GPa. After this pressure transition from true half-metallic behavior to nearly half-metallic behavior is observed and at 90 GPa it shows metallic behavior. Co₂CrGa shows nearly half-metallic behavior at ambient pressure, but true half-metallic behavior is observed as pressure is increased to 100 GPa. For Co₂VGa, true half-metallic to nearly half-metallic transition is observed at 40 GPa and around 100 GPa, Co₂VGa shows metallic behavior. For Co₂VAl, true half-metallic behavior is not observed at ambient as well as higher pressures. The half metal-to-metal transition in Co₂VAl and Co₂CrAl is accompanied by quenching of magnetic moment.     

Nonlinear refractive index of RECOB (RE = Gd and La) crystals

The Z-scan technique is employed to obtain the nonlinear refractive index (n ₂) of the Ca₄REO(BO₃)₃ (RECOB, where RE = Gd and La) single crystals using 30 fs laser pulses centered at 780 nm for the two orthogonal orientations determined by the optical axes (X and Z) relative to the direction of propagation of the laser beam (k//Y// crystallographic b-axis). The large values of n ₂ indicate that both GdCOB and LaCOB are potential hosts for Yb:RECOB lasers operating in the Kerr-lens mode locking (KLM) regime.     

Sr4Al14O25:RE3+(RE=Eu,Ce,Tb)中稀土离子的发光性质

采用高温固相反应合成了Sr4Al14O25：RE^3 (RE＝Eu，Ce，Tb)样品，研究了其中Eu^3 ，Ce^3 和Tb^3 的光谱性质，以及Ce^3 与Tb^3 共掺时的能量传递现象；发现Eu^3 ，Ce^3 和Tb^3 占有两个格位，与Eu^2 在此基质中的情况相似；在Tb^3 的发射光谱中同时观察到了来自^5D3与^5D4的发射，表明两能级间无辐射跃迁过程不显著；Ce^3 对Tb^3 有敏化作用。     

热解法制备KY3F10: Yb, RE(RE=Er, Ho, Tm)纳米晶及其特性研究

有机染料和量子点等荧光标记材料存在发射光谱宽、 光热稳定性差和细胞毒性等缺陷, 限制了其在生物学研究中的应用. 镧系掺杂上转换发光材料不存在"自发荧光"和"光漂白"现象, 灵敏度高, 长期稳定性好, 利于活体检测. 论文首次采用热解法, 以油酸和十八烯为表面活性剂和溶剂, 制备了KY₃F₁₀: Yb, RE(RE=Er, Ho, Tm) 纳米晶. 研究了油酸含量对产物形貌和粒径尺寸的影响, 当油酸与十八烯的比例为3:1时, 为制备类球形单分散纳米晶体的最佳工艺条件, 在980 nm半导体激光器激发下, 样品KY₃F₁₀: Yb, RE(RE=Er, Ho, Tm) 分别发射出较强的黄绿、 绿色和蓝色光, 这些结果显示KY₃F₁₀: Yb, RE(RE=Er, Ho, Tm) 纳米粒子作为生物探针在多重荧光标记方面具有优异的特性.     

The generalized planar fault energy,ductility, and twinnability of Al and Al–RE( RE= Sc,Y, Dy,Tb, Nd) at different temperatures:A first-principles study

The genearlized planar fault energies of Al and Al–RE(RE = Sc, Y, Dy, Tb, Nd) alloys have been investigated using first-principles methods combined with a quasiharmonic approach. The stacking fault energies, unstable stacking fault energies, and unstable twinning energies decrease slightly with increasing temperature. The ductility parameter D,the relative barrier difference utδus, and the twinnability τa of Al and Al–RE alloys at different temperatures have been determined. It is found that the ductilities of Al and Al alloys are nearly the same and the ductilities increase slightly with increasing temperature. The RE alloying elements make twinning more likely and the twinnabilities of Al and Al alloys decrease with increasing temperature.     

La在La:PWO闪烁晶体中的作用机制探讨

根据掺La的PWO晶体(LaPWO晶体)的透射光谱和发射光谱随La浓度的变化特性及其电子顺磁共振(EPR)谱,作者认为,掺La使晶体产生了新的以(LaPb)2/3(VPb)1/3WO4为主的缺陷,LaPWO晶体的透光性能的改善主要是由于Pb空位(VPb)"的增加.而发光性能的降低则主要是(LaPb)和(VPb)"的共同作用.     

One-pot synthesis of oleic acid-capped cadmium chalcogenides (CdE: E = Se,Te) nano-crystals

Surface-capped CdSe and CdTe nano-crystals (NCs) have been synthesized using cadmium acetate, oleic acid and respective tri-octylphosphine chalcogenide (TOPE; E = Se/Te) in diphenyl ether (DPE). Well-dispersed CdSe particles showed two absorption bands at the region of 431–34 and 458–60 nm in optical absorption study. A band-edge emission resulted at 515 nm with an excitation energy of 400 nm, in its photoluminescence (PL) spectrum. Similarly, UV–visible absorption study of CdTe revealed an absorption band at <700 nm. The broadened X-ray diffraction (XRD) pattern showed that at higher reaction temperature cubic CdSe but hexagonal CdTe can be obtained with crystallite size of <10 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that agglomerated particles are of spherical nature. The inter-planar spacing in CdTe was measured to be 0.406 nm, a characteristic of (100) lattice plane in hexagonal CdTe. X-ray photoelectron spectroscopy (XPS) showed that CdSe NCs have better air stability stable than CdTe. Presence of organic moiety around the semiconductor particles was confirmed by infra-red (IR) spectroscopy.     

Structural characterization,magnetic properties and magnetocaloric effects of La0.75Sr0.25Mn1–x Cr x O3 (x = 0.15, 0.20, and 0.25)

The effect of Cr doping on the structural, magnetic and magnetocaloric properties of perovskite manganites La_0.75Sr_0.25Mn_1–x Cr _x O₃ (x = 0.15, 0.20, and 0.25) has been investigated. Crystalline structure and magnetic properties are investigated by using X-ray powder diffraction and magnetization measurements, respectively. All samples show a single phase and are found to crystallize in the distorted rhombohedral system with \( R\overline{3} \,c \) space group. A monotonous change of Curie temperature (T _C), from 314 to 253 K, is observed when content doping increases. Substantial magnetic entropy change reaching 4.20 J/kg K is revealed. Relative cooling power was estimated as well. It was found to reach 289, 323, and 386 J/kg for x = 0.15, 0.20, and 0.25, respectively. Field dependence of the magnetic entropy change showing the power law dependence \( \Delta S_{\rm M} \propto \,\,\left( {\mu_{ 0} \rm H} \right)^{n} \) is also analyzed and discussed.     

非晶态RE—TM(RE=Nd,Pr,TM=Fe,Co,Ni)薄膜的磁性和Pr的变价行为

本文通过对非晶态轻稀土Pr,Nd和过渡族金属Fe,Co,Ni薄膜合金的低温磁性研究,分别得到了(Pr,Nd)_x-(Fe,Co,Ni)_1-x合金中Pr,Nd和Fe,Co,Ni金属磁矩随成份x的变化,并且通过对磁矩的研究得到Pr离子的4f电子可能有退局域化的结论。 关键词：     

RE2O3 (RE = Lu, Y, Sc)的氧空位第一性原理计算研究

本研究选择三个电子结构类似的稀土倍半氧化物RE₂O₃(RE=Lu, Y,Sc),建立适当的模型通过第一性原理计算,研究氧空位对体系的电子结构的影响.本研究以密度泛函理论(DFT)为基础,利用PBE泛函加U值修正计算了纯稀土倍半氧化物的能带结构.计算结果表明三种基体材料RE₂O₃的能带结构相似.在引入氧空位后,其增加的缺陷能级数目不同,依次为:Sc₂O₃2O₃2O₃.     

РАДИАЦИОННЫЙ ЗАХВАТ НЕЙТРОНА ЯДРАМИ Sc,Fe, Cu,Mo, Cd и La

, . 20–1000 keV Sc, Fe, Cu, Mo, Cd La.

---

The radiative capture of a neutron on Sc, Fe, Cu, Mo, Cd and La nuclei

The energies and intensities of the transitions of a compound nucleus, produced by the capture of a neutron, were measured by means of a single-crystal scintillation spectrometer. The region of energies 20–1000 keV was measured on Sc, Fe, Cu, Mo, Cd and L a nuclei.

     

LaGaO3:RE3+(RE3+=Eu3+,Ho3+)的光谱

本文用固态反应合成了钙钛矿型的LaGaO3和LaGaO3:RE3+(RE3+=Eu3+,Ho3+)荧光体,并观察了物相随不同的激活离子浓度的变化。测量了化合物在室温下的反射光谱,激发光谱和荧光光谱。研究了Eu3+的D0→7F2和Ho3+的5S2→5I8的荧光强度与激活离子浓度的关系,发现了浓度猝灭,并得到了最大荧光强度的浓度值。     

(Sr,Ba)Al12O19:RE3+(RE=Ce,Tb)的VUV发光及Ce3+→Tb3+的能量传递

采用高温固相反应合成磁铅矿型(Sr,Ba)Al12O19:RE3 (RE=Ce,Tb)发光材料,X射线衍射结果证明生成单一磁铅矿型结构.Ce3 产生302 nm的发射峰和340 am左右的不太明显的肩,分别对应于5d→2F5/2和5d→2F7/2跃迁;激发光谱显示两个宽带峰,158 nm峰对应于基质吸收,260 nm峰是由4f-5d跃迁引起的.Tb3 的发射光谱显示特征的.D3→1Fi(i=2,3,4,5)和5D4→7Fi(i=4,5,6)跃迁;在激发光谱中,160 nm左右的峰是由基质吸收和Tb -O2-电荷迁移带交迭产生的,193 nm峰是Tb3 的4f-5d自旋允许跃迁引起的,233 nm弱的峰是自旋禁戒4f-5d跃迁产生的.Ce3 的发射和Tb3 的f-f跃迁吸收(～320 nm)完全交迭,并且Tb3 的发光强度随Ce3 的浓度增加而增强,从激发光谱看出,Tb3 发光部分来自于Ce3 的0吸收,具有Cd →Tb3 能量传递.     

纳米发光材料LnVO4:Eu(Ln=La,Gd,Y)的光谱研究

采用络合溶胶 凝胶法制备了系列纳米发光材料LnVO4:Eu(Ln =La ,Gd ,Y) ,并采用X射线衍射(XRD)、红外光谱 (FTIR)、荧光光谱以及紫外 可见光谱 (UV Vis)对三种发光材料的结构以及发光性质进行研究。结果表明 :YVO4与GdVO4具有相同的结构 ,均属于四方晶系 ,二者具有相似的光谱性质 ;而LaVO4属于单斜晶系 ,受对称性的影响其光谱也相应的发生了变化 ,红外光谱和发射光谱的特征峰发生明显的宽化 ,紫外光谱峰的数目增多     

CaAl3BO7：RE(RE=Ce,Gd,Tb)中稀土离子的光谱特性

采用固相反应法合成了CaAl₃BO₇RE(RE=Ce,Gd,Tb),研究了Ce³⁺,Gd³⁺和Tb³⁺的光谱特性。发现铈离子周围存在较强的晶场,使基态的4f能级劈裂较大,从而导致铈离子的特征发射峰重叠较大;Ce³⁺的5d能级明显低于Gd³⁺的⁶I、⁶P能级;Ce³⁺和Tb³⁺之间存在有效的能量传递。     

燃烧法合成Ln_2O_2S∶RE~(3+)(Ln=Gd,La;RE=Eu,Tb)X射线荧光粉及发光性能

采用燃烧合成法,以稀土硝酸盐和二硫代乙二酰胺为反应物,通过控制两者的摩尔比例,在点燃温度为300 ~350℃时,制备了掺杂不同浓度稀土激活剂离子的硫氧化物X射线荧光粉。分别以X射线衍射(XRD)、扫描电子显微镜(SEM)、光致发光(PL)光谱及X射线激发的发光(XEL)光谱对样品进行了表征。XRD分析表明,当热处理温度低于500℃时,可得到单一相的硫氧化物X射线荧光粉,这就避免了高温烧结的缺点;而当烧结温度较高时,开始有硫酸氧化物出现。从SEM图像中可以看到荧光粉粉末具有疏松和多孔连续的三维的网络块状结构,但其初级粒子尺寸较小,均小于50nm,这在一定程度上,可以提高成像系统的空间分辨率。PL光谱分析表明,所制备的荧光粉样品分别呈现出Eu3+,Tb3+离子的特征发射。XEL光谱结果表明,尽管它与光致发光的激发原理不一样,但同样呈现出Eu3+,Tb3+离子的特征发射;这些样品本身对X射线的吸收系数及掺杂浓度不一样,因此它们的光发射效率也有所差别。     

红外激发的高效绿色磷光体—NaLnF:Yb~(3 )Er~(3 )(Ln:Y,Gd,La)

发现六角型的NaLnF_4∶Yr~(3 ),Er~(3 )在红外激发下,是一种高效的发绿光的磷光体。它是由NaSiF_6和共沉淀的Ln_(1-Y-Z)Yb_yEr_2F_3的混合物在630℃于氩气氛中灼烧而制备的。实验表明,NaYF_4∶Yb~(3 ),Er~(3 )的最佳灼烧条件如下:(a)NaSiF_6→2NaF SiF_4的分介反应是完全的。(b)液体的NaF—NaY_(1-Y-Z)Yb_YEr_ZF_4和六角型的NaY_(1-Y-Z)Yb_YEr_ZF_4是共存的。以及(c)NaY_(1-Y-Z)Yb_YEr_ZE_4从六角到立方的相变不出现。当用Si掺杂GaAs二极管激励时,适当制备后的NaY_(0.57)Yb_(0.39)Er_(0.04)E_4的发光亮度是市场出售的LaF_3∶Yb~(3 )Er的4—5倍。