Rare Earth Centered Hybrid Materials: Tb<Superscript>3+</Superscript> Covalently Bonded with La<Superscript>3+</Superscript>, Gd<Superscript>3+</Superscript>, Y<Superscript>3+</Superscript> Through Sulfonamide Bridge and Luminescence Enhancement

The organic ligand 5-sulfosalicylic acid (SSA) is grafted by (3-aminopropyl) triethoxysilane (APTES) to achieve functionalized sulfonamide bridge (SSA-Si) which can both coordinate to Ln³⁺ to form luminescent center and link inorganic Si-O network through hydrolysis and condensation reaction with tetraethoxysilane (TEOS). Thus the organic–inorganic hybrid is obtained with sol-gel method. The organic polymer poly-methyl methacrylate (PMMA) acts as another precursor is prepared through the direct addition polymerization of MMA monomer in the presence of the initiator BPO (benzoyl peroxide). The two kinds of precursors are coordinated to the Ln³⁺ simultaneously to form organic–inorganic-polymeric hybrids which contain both inorganic Si-O-Si net and organic periodic C–C chains. In these complicated compounds we intercalate different ratios of Tb³⁺ and inert lanthanide ion (La³⁺, Gd³⁺, Y³⁺) and find that the introduction of the inert lanthanide ions can enhance the luminescence intensity. This enhancement phenomenon is called co-luminescence effect which is studied by emission spectra in this paper.     

Luminescent molecular hybrid system derived from 2-furancarboxylic acid and silylated monomer coordinated to rare earth ions

In this study, silica-based organic-inorganic hybrids were prepared by the sol-gel method. Tetraethoxysilane (abbreviated as TEOS) and a kind of monomer (abbreviated as FA-APES) derived from modified 2-furancarboxylic acid (abbreviated as FA) with (3-aminopropyl)triethoxysilane (abbreviated as APES) were used as the inorganic and organic fragments, respectively. Coordination reaction between lanthanides (europium and terbium ions) and CO group of the monomer happened simultaneously. And after days of aging process the resultant materials showed characteristic luminescence of lanthanides. The enhancement of luminescence can be seen by the comparison with simply doped lanthanide hybrid systems. And it can be explained by the coordination ability of the organic counterpart. IR, NMR, UV-vis absorption, low-temperature phosphorescence spectroscopy and fluorescence spectroscopy were applied to characterize and the above spectroscopic data revealed that the triplet state energy of organic ligand matches with the emissive energy level of lanthanides (especially of Tb³⁺).     

Luminescence properties of Tb and Eu-doped alumina films prepared by sol-gel method under various conditions and sensitized luminescence

Rare earth ion (Tb³⁺ and Eu³⁺)-doped alumina films were prepared by the aqueous sol-gel method under various conditions. The influences of the OH groups (phonon relaxation) and rare earth ion concentration (cross-relaxation) on luminescence were examined. In regard to the former relaxation, at treatment temperature above 600°C, reciprocal lifetime decreased with OH concentration, and below 500°C, decreased markedly and nonlinearly. On the other hand, in regard to the latter relaxation, there was negligible effect on luminescence for these doped films. The quantitative treatment was tried to lifetime considering these influences. Tb³⁺ and Eu³⁺ co-doped alumina films showed enhanced Eu³⁺ luminescence by the energy transfer from Tb³⁺ to Eu³⁺. Eu³⁺ luminescence intensity increased with a greater Tb³⁺ concentration.     

Lanthanide-Containing 2,2′-Bipyridine Bridged Urea Cross-Linked Polysilsesquioxanes

Urea-based bis-silylated 2,2′–Bipyridine (bpy) organic–inorganic hybrids incorporating different lanthanide (Ln³⁺) ions (Eu³⁺, Gd³⁺, Tb³⁺ or Eu³⁺/Tb³⁺) were obtained by the sol–gel process. The structure and the emission characteristics of the hybrids were ascertained using X-ray diffraction, nuclear magnetic resonance, Fourier transform infrared spectroscopy, photoluminescence, and quantum yield measurements. The hybrids feature both the emission of the host and the Eu³⁺ and/or Tb³⁺ transitions allowing a fine-tuning of the color from the blue to the red, orange, or green spectral regions. Bpy-to-Ln³⁺ and Tb³⁺-to-Eu³⁺ energy transfer mechanisms are demonstrated and the hybrids present slightly distinct Ln³⁺ coordination spheres due to the different bpy/Ln³⁺ ratios.     

Low temperature quenching and high efficiency Tm, La or Tb co-doped CaSc2O4:Ce phosphors for light-emitting diodes

Low temperature quenching and high efficiency CaSc₂O₄:Ce³⁺ (CSO:Ce³⁺) phosphors co-doped with Tm³⁺, La³⁺ and Tb³⁺ ions were prepared by a solid state method and the phase-forming, morphology, luminescence and application properties of these phosphors were investigated. The results showed that co-doping of Tm³⁺, La³⁺ and Tb³⁺ ions can improve the luminescence properties and decrease temperature quenching of CSO:Ce³⁺ phosphor remarkably. High efficiency green-light-emitting diodes were fabricated with the prepared phosphors and InGaN blue-emitting (∼460 nm) chips. The good performances of the green-light-emitting LEDs made from co-doped CSO:Ce³⁺ phosphors confirm the luminescence enhancement and indicate that Tm³⁺, La³⁺ and Tb³⁺ co-doped CSO:Ce³⁺ phosphors are suitable candidates for the fabrication of high efficiency white LEDs.     

Molecular Design and Fluorescent Whitening Emission from Novel Lanthanide Activated Organic–Inorganic Covalently Hybrid Micro-particles

A series of potential lanthanide activated fluorescent-whitening hybrid micro-particles has been prepared by sol-gel method. The precursor derived from 2,2′-dipyridylamine derivative modified though hydrogen transfer addition exhibited a self-organization under the coordination to RE³⁺ (Eu³⁺, Tb³⁺, Sm³⁺, Dy³⁺, respectively) evaluated by SEM (micrometric scale) and X-ray diffraction studies (nanometric scale). The adapting traditional routes used in this paper affected the shape of the materials and can be taken as a new method to control the hydrolysis-polycondensation process. Fourier transform infrared (FTIR), Diffuse reflectance ultraviolet-visible spectra (DRUVS) and ¹H NMR spectra were used to confirm the modifications. These activated phosphors with lanthanide ions represent a novel way to produce fluorescent whitening agents.     

Spin-glass like behaviors in La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Tb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> perovskite

A series of samples of La_1−x Tb _x MnO₃ (0⩽x⩽0.15) are prepared. The static and dynamic magnetizations of La_1−x Tb _x MnO₃ have been investigated. The results indicate that the spins with the short-range order are frozen into random direction at low enough temperatures which leads to the samples exhibiting the spin-glass like behavior. It is considered that the spin-glass like behavior originates from the competition between ferromagnetic double exchange among Mn³⁺ and Mn²⁺ and antiferromagnetic superexchange among Mn³⁺ and Mn³⁺, as well as Tb³⁺ and Tb³⁺.     

Excitation process and photoluminescence properties of Tb and Eu ions in SnO2 and in SnO2: Porous silicon hosts

Tin oxide (SnO₂)-layers-doped terbium and europium ions are elaborated by the sol-gel method on silicon substrates. After annealing at 500 °C, the transmission electron microscopy revealed a crystallization of tin oxide.The emission properties of rare-earth in SnO₂ are studied systematically against temperature annealing and Tb³⁺ concentration. The PL spectrum is optimal after annealing at 900 °C and the corresponding photoluminescence (PL) decay is nearly exponential, showing that the sample is homogenous and the PL process can be described by two levels system.The concentration effect shows a quenching of the PL intensity for Tb³⁺ concentration above 4%. From the investigation of the decay rate from the ⁷F₅ state within terbium concentration, we show that self-quenching is insured by dipole - dipole interaction. The evolutions of both PL intensity and PL lifetime versus temperature are studied. The PL intensity and PL lifetime are enhanced by deposing SnO₂:Tb³⁺ and SnO₂:Eu³⁺ in porous silicon. We show that an efficient excitation transfer from Si nanocrystallites to RE ions can occur.     

In situ sol-gel composition of multicomponent hybrid precursor to hexagon-like Zn2SiO4:Tb microcrystalline phosphors with different silicate sources

Zn₂SiO₄ doped with Tb³⁺ were in situ synthesized by a modified sol-gel technology with the assembly hybrid precursor employed four different silicate sources, i.e. 3-aminopropyl-trimethoxysilane (APMS), 3-aminopropyl-triethoxysilane (APES), 3-aminopropyl-methyl-diethoxysilane (APMES) and tetraethoxysilane (TEOS), respectively. The SEM result shows that there exist some novel unexpected micromorphological structures of hexagon-like with the dimension of 0.5-1.0 μm. The photoluminescent properties of Zn₂SiO₄:Tb³⁺ phosphors have been studied as a function of Tb³⁺ doping concentration. Cross-relaxation process between identical Tb³⁺ ions results in the quenching of the ⁵D₃ emission for high concentration sample.     

NMR studies of singlet-ground-state rare-earth ions in high-T c superconductors

Many of presently known high-T _c superconductors contain rare-earth (RE) ions with an even number of electrons in an unfilled 4f-shell (Pr³⁺, Tb³⁺, Ho³⁺, Tm³⁺). If the ground state of 4f-electrons is non-degenerate and separated from excited states by high enough energy intervals, one can observe the so-called “enhanced NMR” of RE nuclei at low temperatures. In the present paper some aspects of the enhanced NMR are analyzed in applications to the crystal and electron structure of high-T _c superconductors.     

Post annealing immersion: A new technique for studying rare earth ions in porous materials

A novel technique is introduced for studying how rare earth ions are incorporated into the matrix of porous materials. Tb³⁺-doped silica sol-gel is annealed to form porous glass and immersed in an aqueous Gd(NO₃)₃ solution. Re-heating removes the liquid and deposits Gd³⁺ ions on the internal pore surfaces. Spectroscopic investigation of Gd³⁺→Tb³⁺ energy transfer yields information about the location of Tb³⁺ dopant ions relative to pore surfaces. Results from post-annealing immersion experiments indicate that most Tb³⁺ dopant ions are close to pore surfaces when sol-gel glass is annealed to 700 °C. The observed energy transfer decreases with higher annealing temperatures, indicating that Tb³⁺ dopants in densified regions are isolated from Gd³⁺ ions deposited on pore surfaces. Al³⁺ co-doping affects both the overall sample density and the degree of Gd³⁺→Tb³⁺ interaction in post-annealing immersion samples.     

Synthesis and luminescence properties of Eu, Ce and Tb-activated Sr3La2(BO3)4 under UV excitation

The spectroscopic properties in UV-excitable range for the phosphors of Sr₃La₂(BO₃)₄:RE³⁺ (RE³⁺=Eu³⁺, Ce³⁺, Tb³⁺) were investigated. The phosphors were synthesized by conventional solid-state reactions. The photoluminescence (PL) spectra and commission international de I'Eclairage (CIE) coordinates of Sr₃La₂(BO₃)₄:RE³⁺ were investigated. The f-d transitions of Eu³⁺, Ce³⁺ and Tb³⁺ in the host lattices are assumed and corroborated. The PL and PL excitation (PLE) spectra indicate that the main emission wavelength of Sr₃La₂(BO₃)₄:Eu³⁺ is 611 nm, and Sr₃La₂(BO₃)₄:Ce³⁺ shows dominating emission peak at 425 nm, while Sr₃La₂(BO₃)₄:Tb³⁺ displays green emission at 487, 542, 582 and 620 nm. These phosphors were prepared by simple solid-state reaction at 1000 °C. There are lower reactive temperature and more convenient than commercial phosphors. The Sr₃La₂(BO₃)₄:Tb³⁺ applied to cold cathode fluorescent lamp was found to emit green light and have a major peak wavelength at around 542 nm. These phosphors may provide a new kind of luminescent materials under ultraviolet excitation.     

The specific heat jump of superconducting La1-xTbxAl2 related to crystal electric field splitting of the Tb3+ levels

Measurements of the specific heat jump Δc(Tinc) were performed on superconducting La_1-xTb_xAl₂ compounds in order to investigate the pairbreaking effect of Tb³⁺ ions in the LaAl₂ host. The results deviate from the Abrikosov-Gorkov theory for superconductors with magnetic impurities. Taking into account the crystal field level structure of Tb³⁺ in LaAl₂ the results can be qualitatively understood within the model of Fulde, Keller and Peschel. According to calculations published by Müller-Hartmann and Zittartz an influence of the Kondo effect can be ruled out.     

Effect of Tb3+ concentration on luminescence properties of Ce/Tb/Eu co-doped borosilicate glasses for white LEDs

Ce, Tb and Eu single and ternary doped borosilicate glasses were prepared and effect of Tb³⁺ concentration on luminescence properties of ternary co-doped glasses were analyzed by utilizing emission spectra, excitation spectra, the Commission International de I’Eclairage (CIE) colorimetric system and fluorescence decay curves. The results show that Tb³⁺ concentration significantly affects spectral intensities of ternary co-doped glasses when excited by near ultraviolet (NUV). With the increasing of Tb³⁺ concentration, the blue emission of Ce³⁺ is weakened and the red emission of Eu³⁺ is slightly enhanced. Both the color coordinates and correlated color temperatures (CCTs) can be adjusted by Tb³⁺ concentration. Besides, the energy transfers from Ce³⁺ to Tb³⁺ and from Tb³⁺ to Eu³⁺ were observed. Measured characteristic lifetimes of Tb³⁺ indicate that the energy transfer from Ce³⁺ to Tb³⁺ tends to predominate in whole process. The studies show that Ce/Tb/Eu ternary doped borosilicate glasses might be promising luminescence materials for NUV pumped white LEDs.     

用溶胶-凝胶方法制备Tb3+掺杂的硅基发光材料

报道了用溶胶-凝胶方法制备Tb³⁺掺杂的硅基发光材料.并用荧光光谱、傅里叶变换红外光谱、原子力显微镜、差热分析和热重测定等方法研究了材料的制备规律.实验结果表明该制备方法在500℃的退火条件下即可以使Tb³⁺掺杂到硅基发光材料产生室温下的545nm荧光;稀土离子的掺杂浓度可任意调节,最佳浓度为5×10¹⁹/cm³;薄膜在微米量级上有较好的平整度.用该方法在改善材料的掺杂浓度、发光性能及降低材料的退火温度方面有特殊的优越 关键词：     

The influence of crystal field split impurities (Tb) on the superconducting properties of LaAl2

The superconducting transition temperatures of the system La_1-xTbxAl₂ have been measured. By making use of the theory of Keller and Fulde the energy splitting between the ground state and the first excited state of Tb³⁺ is found to be 5 ± 1 K. Furthermore, we have determined the upper critical field H_c2(T) of these alloys and compared the results with those found for La_1-xGd_xAl₂. In this way the influence of the crystal field splitting of Tb³⁺ on the critical field data is clearly demonstrated.     

Sensitized luminescence through nanoscopic effects of ZnO encapsulated in SiO2:Tb sol gel derived phosphor

Terbium (1 mol%) doped ZnO-SiO₂ binary system was prepared by a sol-gel process. Nanoscopic effects of ZnO on the photoluminescence (PL) and the cathodoluminescence (CL) properties were studied. Defects emission from ZnO nanoparticles was measured at 560 nm and the line emission from Tb³⁺ ions in SiO₂:Tb³⁺ and ZnO-SiO₂:Tb³⁺ with a major peak at 542 nm was measured. The PL excitation wavelength for 542 nm Tb³⁺ emission was measured at ∼320 nm in both SiO₂:Tb³⁺ and ZnO-SiO₂:Tb³⁺. The CL data showed quenched luminescence of the ZnO nanoparticles at 560 nm from a composite of ZnO-SiO₂:Tb³⁺ and a subsequent increase in 542 nm emission from the Tb³⁺ ions. This suggests that energy was transferred from the ZnO nanoparticles to enhance the green emission of the Tb³⁺ ions. The PL and CL properties of ZnO-SiO₂:Tb³⁺ binary system and possible mechanism for energy transfer from the ZnO nanoparticles to Tb³⁺ ions are discussed.     

Ca₂BO₃Cl:Ce³⁺,Tb³⁺:A novel tunable emitting phosphor for white light-emitting diode

<正>Ca₂BO₃Cl:Ce³⁺,Ca₂BO₃Cl:Tb³⁺,and Ca₂BO₃Cl:Ce³⁺,Tb³⁺ phosphors are synthesized by a high temperature solid-state reaction.The emission intensity of Ce³⁺ or Tb³⁺ in Ca₂BO₃Cl is influenced by the Ce³⁺ or Tb³⁺ doping content,and the optimum concentrations of Ce³⁺ and Tb³⁺ are 0.03 mol and 0.05 mol,respectively.The concentration quenching effect of Ce³⁺ or Tb³⁺ in Ca₂BO₃Cl occurs,and the concentration quenching mechanism is d-d interaction for either Ce³⁺ or Tb³⁺.The Ca₂BO₃Cl:Ce³⁺,Tb³⁺ can produce colour emission from blue to green by properly tuning the relative ratio between Ce³⁺ and Tb³⁺,and the emission intensity of Tb³⁺ in Ca₂BO₃Cl can be enhanced by the energy transfer from Ce³⁺ to Tb³⁺.The results indicate that Ca₂BO₃Cl:Ce³⁺,Tb³⁺ may be a promising double emission phosphor for UV-based white light emitting diodes.     

Preparation and luminescence properties of terbium-doped lanthanum oxide nanofibers by electrospinning

Terbium-doped lanthanum oxide (La₂O₃:Tb³⁺) nanofibers were prepared by electrospinning followed by calcination at high temperature. Thermogravimetric analyzer (TGA), field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and photoluminescence (PL) were used to characterize the obtained fibers. The results reveal that the nanofibers have an average diameter of ca. 95±25 nm and are composed of pure La₂O₃ phase. Under the excitation of 274 nm light, the La₂O₃:Tb³⁺ nanofibers exhibit the characteristic emission resulting from the ⁵D₄→⁷F_J (J=3, 4, 5, 6) transitions of Tb³⁺ ions. And the PL emission intensity is stronger than that of their nanoparticle counterparts.     

Magnetic ordering in the T* phase La1.2Tb0.8CuO4

We report a muon spin relaxation study of the magnetic properties of the La_1.2Tb_0.8CuO₄ phase with the T^* structure. Random magnetic order is revealed between 280 and 170 K by the zero field data. A spontaneous muon precession then appears below 170 K, arising from antiferromagnetic long range order of the Cu²⁺ spins. Evidence exists below 20 K for ordering of the Tb³⁺ ions. We find that the T^* phase adopts the same magnetic structure as the (T/O) phase La₂CuO₄.