Au-modified silicon nanowires for surface-enhanced fluorescence of Ln3+ (Ln = Pr, Nd, Ho, and Er)

The interaction of the surface plasmons of gold nanoparticles on silicon nanowires with fluorophores, lanthanide ions (praseodymium ions, Pr³⁺, neodymium ions Nd³⁺, holmium ions Ho³⁺, and erbium ions Er³⁺) was investigated. In the presence of Au/Si nanomaterials, the fluorescence peaks were significantly enhanced, which resulted in about 2 orders of magnitude enhancement. The photoluminescence studies revealed that the enhanced fluorescence originates from the local field enhancement around Ln³⁺ ions, caused by the electronic plasmons resonance of the gold nanoparticles. Results showed that this Au/Si nanostructure had larger enhancement factor than that caused by unsupported Au nanoparticles. These results might be explained by the local field overlap originated from the closed and fixed gold nanoparticles on silicon nanowires.     

Order–Disorder Transformations in Ln2Ti2O7(Ln = Lu, Yb, Tm, Gd)

The ordering processes in the rare-earth titanates Ln₂Ti₂O₇ with Ln = Lu, Yb, Tm, and Gd are studied by x-ray diffraction, thermal analysis, IR spectroscopy, electron microscopy, and electrical conductivity measurements. The compounds are prepared via hydroxide coprecipitation, followed by freeze-drying and heat treatment in the temperature range 350–1700°C. The compounds Ln₂Ti₂O₇ with Ln = Lu, Yb, and Tm are found to have the fluorite structure between 600 and 800°C. Above 800°C, they undergo a fluorite-to-pyrochlore transformation, with cation disordering and the formation of Ln_Ti + Ti_Ln antistructure pairs. Gd₂Ti₂O₇ has the pyrochlore structure over the entire temperature range studied and contains no antistructure defects. In contrast to Gd₂Ti₂O₇, the compounds Ln₂Ti₂O₇ with Ln = Lu, Yb, and Tm undergo a high-temperature pyrochlore-to-fluorite phase transition around 1700°C. The 750°C conductivity of Ln₂Ti₂O₇ (Ln = Lu, Yb, Tm) samples sintered at 1700°C is 5 × 10^–3 to 10^–2 S/cm, which is two orders of magnitude higher than that of ceramics of the same composition prepared at lower temperatures (950 or 1400°C). The conductivity of the Gd₂Ti₂O₇ ceramic prepared at 1500°C is two orders of magnitude lower than that of Ln₂Ti₂O₇ with Ln = Lu, Yb, and Tm.     

Preparation and thermophysical properties of nano-sized Ln2Zr2O7 (Ln?=?La, Nd, Sm, and Gd) ceramics with pyrochlore structure

Rare earth zirconates (Ln₂Zr₂O₇, Ln = La, Nd, Sm, and Gd) with pyrochlore structure were prepared by hydrothermal method with polyethylene glycol as surfactant. X-ray diffraction, thermogravimetric analysis/differential scanning calorimetry, Fourier transform infrared spectroscopy, Raman spectroscopy, and field emission scanning electron microscopy were utilized to characterize the phase structure, thermal decomposition, and morphology of the products. Qualitative analysis indicates that the as-prepared zirconates are pyrochlore-type structures. The specific surface area, lattice parameter, and average crystallite size of the as-prepared products are closely related to the ionic radius. The activation energy of crystal growth shows an increasing trend with the decrease in ionic radii. The sintering behavior of compacted body was also investigated, revealing that the sintering-resistance properties of Ln₂Zr₂O₇ are descending as the order of La₂Zr₂O₇, Nd₂Zr₂O₇, Sm₂Zr₂O₇, and Gd₂Zr₂O₇.     

Interdiffusion of rare-earth cations in Ln1−x ′Ln x ″ Ba2Cu3O7 − δ (Ln′, Ln″ = Y, Dy, Ho) High-T c superconductors

The Y³⁺/Ho³⁺, Y³⁺/Dy³⁺, and Dy³⁺/Ho³⁺ interdiffusion coefficients in the YBa₂Cu₃O_{7 ? δ}-HoBa₂Cu₃O_{7 ? δ}, YBa₂Cu₃O_{7 ? δ}-DyBa₂Cu₃O_{7 ? δ}, and DyBa₂Cu₃O_{7 ? δ}-HoBa₂Cu₃O_{7 ? δ} systems have been determined in air at a temperature of 1233 K by the Boltzmann-Matano method from the yttrium/holmium, yttrium/dysprosium, and dysprosium/holmium concentration profiles across the diffusion zone between two pellets of the high-T _c superconductors. The composition dependences of the interdiffusion coefficients in the solid-solution systems are presented.     

Transport Properties of TlInSe2〈Ln〉 (Ln = Eu, Sm, Yb)

The electrical conductivity and Hall coefficient of TlInSe₂Ln (Ln = Eu, Yb, Sm) were measured between 300 and 900 K. The results were used to determine the band gap, ionization energy of impurities, conductivity type, and Hall mobility of charge carriers in TlInSe₂Ln. The temperature at which the Hall coefficient changes sign is shown to increase with doping level.     

Synthesis and properties of LnBaFeCoO5 + δ (Ln = Nd, Sm, Gd)

LnBaFeCoO_{5 + δ} (Ln = Nd, Sm, Gd) layered oxides have been synthesized and their crystal structure, thermal stability, thermal expansion, electrical conductivity, thermoelectric power, and magnetic susceptibility have been studied. The oxides have a tetragonal structure (sp. gr. P4/mmm) with unit-cell parameters a = 0.3909(2) nm and c = 0.7695(6) nm for Ln = Nd (δ = 0.65), a = 0.3908(3) nm and c = 0.7662(6) nm for Ln = Sm (δ = 0.37), and a = 0.3908(2) nm and c = 0.7613(6) nm for Ln = Gd (δ = 0.37). The LnBaFeCoO_{5 + δ} compounds are antiferromagnetic p-type semiconductors. With decreasing Ln³⁺ ionic radius, their electrical conductivity and linear thermal expansion coefficient decrease and their thermoelectric power and antiferromagnetic ordering temperature increase. Near 518–653 K, the linear thermal expansion coefficient of the LnBaFeCoO_{5 + δ} oxides increases from (12.9–16.6) × 10^?6 to (19.3–26.5) × 10^?6 K^?1, which is due to the release of weakly bound oxygen from the oxides. We have determined parameters of charge transport in the [Fe(Co)O₂] layers in the crystal structure of the LnBaFeCoO_{5 + δ} phases.     

The influence of ionic radii on the grain growth and sintering-resistance of Ln2Ce2O7 (Ln = La, Nd, Sm, Gd)

Rare earth cerium oxides (Ln₂Ce₂O₇, Ln = La, Nd, Sm, and Gd) with cubic-fluorite structure were prepared by hydrothermal method using cetyltrimethyl ammonium bromide as surfactant. X-ray diffraction (XRD), thermogravimetric analysis/differential scanning calorimetry (TG/DSC), Raman spectroscopy, and field emission scanning electron microscopy (FESEM) were utilized to characterize the phase structure, thermal decomposition, and morphology of the products, respectively. Qualitative analyses indicate that the as-prepared products are fluorite-type structures. The lattice parameter and average crystallite size of the products are closely related to the ionic radii. The activation energy of crystal growth shows an increasing trend with the decrease in ionic radii. The sintering behavior of compacted body was also investigated, revealing that the sintering-resistance properties of Ln₂Ce₂O₇ are descending as the order of La₂Ce₂O₇, Nd₂Ce₂O₇, Sm₂Ce₂O₇, and Gd₂Ce₂O₇.     

Lattice Effect on Magnetic and Electrical Properties of Ln2/3Pb1/3MnO3 （Ln=La,Pr, Nd） Films

Lattice effect on magnetic and electrical transport properties of Ln2/3Pb1/3MnO3 （Ln=La, Pr, Nd） films prepared by RF magnetron sputtering technique were investigated. With the decrease of the average ions radius 〈rA〉, the structure of Ln2/3Pb1/3MnO3 （Ln=La, Pr, Nd） targets transit from the rhombohedral phase to the orthorhombic phase, and the Curie temperature reduces rapidly with the decrease of 〈rA〉. The electrical properties show that films are the metallic state which can be fitted to the formula： ρ（T）=ρ0 ＋ ρ1T^2 ＋ ρ2T^4.5 at low temperatures. The temperature range of the ferromagnetic metallic state becomes narrow with the decrease of 〈rA〉. The phenomenon can be explained by the lattice effect.     

Facile synthesis of β-NaYF4:Ln3+ (Ln = Eu, Tb, Yb/Er, Yb/Tm) microcrystals with down- and up-conversion luminescence

β-NaYF₄:Ln³⁺ (Ln = Eu, Tb, Yb/Er, Yb/Tm) hexagonal microrods have been successfully synthesized through a facile molten salt method without any surfactant. X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy, high-resolution transmission electron microscopy, and photoluminescence spectra were used to characterize the samples. It is found that at a preferred reaction temperature of 400 °C, the structure of β-NaYF₄ can gradually transform from microtubes to microrods as reaction time extends from 0.5 to 4 h. Furthermore, as the molar ratio of NaF:RE³⁺ (RE represents the total amount of Y³⁺ and the doped rare earth elements such as Eu³⁺, Tb³⁺, Yb³⁺/Er³⁺, or Yb³⁺/Tm³⁺) increased, the phase of sample transforms from YF₃ into NaYF₄. Under the excitation of 395 nm ultraviolet light, β-NaYF₄:5 %Eu³⁺ shows the emission lines of Eu³⁺ corresponding to ⁵D_0-3 → ⁷F _J (J = 1–4) transitions from 400 to 700 nm, resulting in red down-conversion (DC) light emission. When doped with 5 % Tb³⁺ ions, the strong DC fluorescence corresponding to ⁵D₄ → ⁷F _J (J = 6, 5, 4, 3) transitions with ⁵D₄ → ⁷F _J (green emission at 544 nm) being the most prominent group that has been observed. Moreover, upon 980 nm laser diode excitation, the Yb³⁺/Er³⁺- and Yb³⁺,Tm³⁺- co-doped β-NaYF₄ samples exhibit bright yellow and blue upconversion (UC) luminescence, respectively, by two- or three-photon UC process. The luminescence mechanisms for the doped lanthanide ions were thoroughly analyzed.     

复合氧化物Ln0.67Sr0.33MnO3（Ln=La,Pr,Nd,Sm）的制备,结构与电性

本语文通过共沉淀工艺合成了复合氧化物Ｌｎ０．６７Ｓｒ０．３３ＭｎＯ３（Ｌｎ＝Ｌａ、Ｐｒ、Ｎｄ、Ｓｍ）与传统陶瓷制备方法相比，成相温度降低约４５０℃，经Ｘ射线衍射分析表明，所得复合氧化物为立方钙钛矿结构，晶胞参数随稀土离子半径变化而呈规律性变化，样品的四极法电阻率测试结果表明；样品中的稀土离子Ｌｎ的离子半径对其本身的地电性起决定性的作用，应用双交换理论，样品中的稀土离子Ｌｎ的离子半径对其本身的导电性     

Sol–gel auto-combustion synthesis and luminescence properties of RVO4: Ln3+ (R=La,Gd; Ln=Sm,Er, Ho,Yb/Er) microcrystals

RVO₄: Ln³⁺ (R=La, Gd; Ln=Sm, Er, Ho, Yb/Er) microcrystals were successfully synthesized by a facile and rapid sol-gel method using glycine as the chelating agent. The crystalline structure, morphology and luminescence properties of obtained products were investigated in detail. The peaks of X-ray diffraction (XRD) patterns were well-indexed to the standard RVO₄ patterns, indicating that the Ln³⁺ ions were well doped into the crystalline lattices and had not changed the crystalline structure. The luminescence properties of the samples are systematically studied. The typical peaks of the emission spectra were sharp and intense, revealing energy was transferred efficiently from VO₄ ^3- to Ln³⁺ after excitation. The schematic diagram for energy transfer between the host matrix and doped lanthanide ions were also discussed. The chromaticity coordinates of RVO₄: Ln³⁺ microcrystals were calculated. This work reveals that the rare-earth vanadates are potential candidates as excellent host matrices of phosphors.     

燃烧法合成YVO_4∶Ln(Ln=Eu,Sm)荧光粉及其发光特性

采用柠檬酸和尿素作为燃料,通过燃烧法分别制备了Eu3+和Sm3+单掺的YVO4荧光粉.采用差示扫描量热仪对样品前驱体的热分解特性进行分析,并采用X射线衍射仪、扫描电子显微镜和荧光分光光度计对所得样品的物相、表面形貌、激发光谱和发射光谱进行表征.实验结果表明,所得样品的晶相为YVO4,四方晶系.并讨论了该荧光粉发光性能的影响因素.     

Synthesis and luminescence of BiPO4:Ln3+ (Ln = Ce3+, Tb3+) phosphors

BiPO₄:Ce³⁺ and BiPO₄:(Ce³⁺, Tb³⁺) powders were synthesized by the method of precipitation. The X-ray diffraction patterns show that BiPO₄:Ce³⁺ and BiPO₄:(Ce³⁺, Tb³⁺) samples have pure hexagonal phases. The transmission electron microscopy results show that the synthesized samples are nanoparticles. Ethylene glycol plays an important role in the formation of nanoparticles. The excitation spectrum of BiPO₄:Ce³⁺ sample shows the transition from the ground ² F _5/2 state to the excited 5d states of the Ce³⁺ ions. The emission spectrum exhibits a strong band centered at 352 nm originating from the 5d → 4f transitions of the Ce³⁺ ions. The emission spectrum of the BiPO₄:(Ce³⁺, Tb³⁺) sample contains both a weak emission band of the Ce³⁺ ions and strong green emission bands of the Tb³⁺ ions. The excitation and emission spectra show that there are energy transfers between Ce³⁺ and Tb³⁺ ions in the BiPO₄:(Ce³⁺, Tb³⁺) sample. The energy transfers between Ce³⁺ and Tb³⁺ ions improve the emission efficiency of BiPO₄:(Ce³⁺, Tb³⁺) sample.     

Synthesis and Study of Uranates of Rare-Earth Elements of Compositions LnU3O10.5·6H2O (Ln = La,Ce, Pr,Nd, Sm), LnU6O19.5·10H2O (Ln = Nd,Sm, Eu,Gd, Tb,Dy), and LnU2O7.5 (Ln = Dy,Ho, Er,Tm, Yb,Lu)

Radiochemistry - The interaction of synthetic skupite UO3·2.25H2O with aqueous solutions of La, Ce, Pr, Nd, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu nitrates under hydrothermal conditions at a...     

Synthesis of Ln0.6Sr0.4Co0.8Fe0.2O3 – δ (Ln = La, Pr, Nd, Sm) Perovskite-like Phases

Ln_0.6Sr_0.4Co_0.8Fe_0.2O_{3 –} (Ln = La, Pr, Nd, Sm) solid solutions are prepared by a procedure which makes it possible to markedly reduce the synthesis temperature and duration. X-ray diffraction, microstructural analysis, and density measurements are used to optimize conditions for the fabrication of dense substituted-cobaltite ceramics.     

Phase Relations in the Systems Ln1 – x Ba x CoO3 – δ(0 < x ≤ 0.66; Ln = Nd, Sm)

Data are presented on the structural and magnetic properties of Ln_{1 – x} Ba _x CoO_{3 –} (Ln = Nd, Sm; 0 < x 0.66) samples slowly cooled in air after synthesis. The composition stability limits of the intermediate phases Ln_{1 – y} Ba_{1 + y} Co₂O_{5 +} and solid solutions are determined. The magnetic phase diagram of the Nd_{1 – x} Ba _x CoO_{3 –} system is constructed.     

Photoluminescence and thermal properties of a red-emitting LnNbO4:Pr3+ (Ln = La,Gd, and Y) phosphor for warm WLEDs

Journal of Materials Science: Materials in Electronics - Efficiently red-emitting Pr3+-doped LnNbO4 (Ln?=?La, Gd, and Y) phosphors have been successfully prepared by the traditional...     

LuTaO4:Ln3+(Ln=Eu,Tb)透明薄膜制备改进与其发光性能研究

LuTaO₄是一种新型的辐射探测材料, 但是制备高质量的透明薄膜面临着巨大挑战。为了在保证薄膜不开裂与高透明度的前提下提高薄膜的厚度, 通过大量摸索选用聚乙烯吡咯烷酮(PVP)为胶黏剂并优化溶胶中固含量及PVP含量成功制备出单层厚度达到100 nm的LuTaO₄:Ln³⁺(Ln=Eu,Tb)薄膜, 保证了薄膜的透明度同时大大提高了发光性能。该方法为高质量LuTaO₄:Ln³⁺(Ln=Eu,Tb)厚膜的制备和应用奠定了基础。