Molecular assembly,luminescence and morphology of novel zinc/inorganic/organic nanohybrid material with covalent linkage

Polyethylene glycol (PEG) was first modified by an inorganic component of 3-(triethoxysilyl)-propyl isocyanate (TEPIC) to form the inorganic/organic polymeric functional precursor. The modified reagent with a functional group (–NHCOO–) further behaves as a bridge which can coordinate to Zn²⁺ through oxygen atom and further formed Si–O backbones after hydrolysis and polycondensation processes. Subsequently, the corresponding organic/inorganic molecular-based hybrids were assembled to behave as the structural polymeric ligands with the two components equipped with covalent bonds. Finally, ternary zinc/inorganic/organic polymeric hybrid materials with chemical bond (covalent bonds of –CO–NH– and Si–O, coordination bond of Zn–O–C) have been assembled. The resulting hybrids exhibit blue luminescence and nanometer morphology.     

Novel polymer–inorganic hybrid materials fabricated with in situ composition and luminescent properties

A new polymer–inorganic material was synthesized from terephthalic acid (TPA) and rare-earth ion (Tb³⁺, Eu³⁺) complex, which rare-earth ions connect with polymer by covalent bands. The luminescent europium and terbium coordination polymers, PET–Tb and PET–Eu, were produced in situ through low temperature solution polycondensation (PET = polyethyl terephthate ester). FTIR spectroscopy, ultraviolet absorption and scanning electron microscopy were applied to characterize the structure of obtained hybrid material. Phosphorescence and fluorescence spectra were applied to characterize the photophysical properties of the obtained hybrid material. The experimental result shows that the strong luminescence of rare-earth ions substantiates optimum energy match and effective intramolecular energy transfer between the triplet state energy of coordination complex and the emissive energy level of the rare-earth ions. The hybrid material systems can be expected to have potential applications in photophysical sensors.     

Tb3+ luminescence enhancement of YAG:Tb3+ nanocrystals embedded in silica xerogel

The luminescence behavior of composite materials consisting of nanocrystals of Y_3?xAl₅O₁₂:Tb (YAG:Tb³⁺) embedded into silica xerogel has been studied. Blue and green luminescence of the materials is due to a cross-relaxation effect in Tb³⁺ ions doped into a YAG lattice. The materials with YAG:Tb³⁺ nanocrystals immobilized in silica exhibit enhancement of Tb³⁺ luminescence in comparison with the macrocrystalline YAG:Tb³⁺ powder. The Tb³⁺ luminescence intensity of a composite material dried at room temperature can be improved when higher aliphatic alcohols are applied in a one-pot procedure during a sol–gel synthesis. On the other hand, the Tb³⁺ luminescence is quenched in the presence of Ag nanoparticles in the material. The composite material (YAG:Tb³⁺ in silica) exhibits thermal stability at higher temperatures and achieves the highest emission intensity after having been annealed at 700 °C.     

Liquid Crystalline and Luminescent Behavior of Lanthanide Complexes Composed of Terbium or Europium and Dendritic Amphiphile

Luminescent lanthanide (Tb³⁺, Eu³⁺) complexes were prepared by reaction of Tb³⁺ or Eu³⁺ with dendritic amphiphile (3,4,5-tris(dodecyloxy)benzoate), then their liquid crystalline and luminescent behavior were studied. The complexes exhibited thermotropic liquid crystalline mesophases with columnar hexagonal structure. The complexes emitted the characteristic luminescence of the core metals. Additionally, in the Eu³⁺ complex, the ratio of the intensity of 614 nm to the intensity of 585 nm (I₆₁₄/I₅₈₅) remarkably decreased around the transition temperature from crystal to mesophase, suggesting that the coordination environment of Eu³⁺ gets more symmetrical due to the phase transition.     

Synthesis and luminescent properties of novel RENbO4:Ln3+ (RE = Y, Gd, Lu; Ln = Eu, Tb) micro-crystalline phosphors

Using rare earth coordination polymers with aromatic carboxylic acids as the precursors of rare earth oxide components, with polyethylene glycol (PEG) as the dispersing media, micro-crystalline phosphors RENbO₄:Ln³⁺ (RE = Y, Gd, Lu; Ln = Eu, Tb) have been synthesized by an in situ co-precipitation method. Both X-ray diffraction and scanning electron microscopy have shown that the resultant samples present are crystalline with ‘rice glue ball’ micro-morphology and crystalline grain sizes in the range of 1–2 μm. The luminescent properties of these phosphors have been studied, which show that the best photoluminescent performance is achieved for GdNbO₄:Tb³⁺ or Eu³⁺. This was because Gd³⁺ plays an important role to enhance the luminescence of Tb³⁺ or Eu³⁺ in an energy transfer process. In addition, the influence of the doping concentration on the fluorescence behaviors has been examined. With increase of the doping concentration from 1 mol% to 5 mol%, both the red emission intensity of Eu³⁺ and the green emission intensity of Tb³⁺ increase.     

Sol–gel synthesis and photoluminescence of RE3BO6: Eu3+/Tb3+ (RE = Y, Gd) microcrystalline phosphors from hybrid precursors

Novel phosphors of Eu³⁺/Tb³⁺ doped RE₃BO₆ (RE = Y, Gd) have been prepared using an original modified in situ sol–gel synthesis route. Different optimized organic media were mixed with rare earth coordination polymers, and tri-n-butyl borate was added to assemble inorganic/organic multi-component hybrid precursors. After calcinations of the resulting precursors at 1000 °C, target phosphors were obtained. The microstructure and morphology information of the phosphors were investigated via the technique of X-ray powder diffraction (XRD) and scanning electronic microscopy, and it has been shown that these phosphors present symmetrical distribution and high packing density, whose grain sizes were around 200 nm. Analyzed by luminescent spectra, these phosphor particles show narrow lines of emissions respectively originating from their characteristic transitions, and the dominating emission peak is due to the hypersensitive transition. The RE₃BO₆: Eu³⁺/Tb³⁺ (RE = Y, Gd) phosphors can be expected to gain more practical applications in commercial phosphors and other luminescent materials used in advanced devices.     

Radiation damage of silicate glasses doped with Tb and Eu

In this work, we studied a set of Tb³⁺ (or Eu³⁺) doped silicate glasses in which some amounts of BaO were added to increase glass density. The irradiation-induced damage was investigated by absorbance measurements performed before and after each irradiation with doses ranging from 3 to 237 Gy. Analysed glasses underwent also light yield measurements investigated in terms of light production. The results showed that radiation damage and light yield depend on glass composition and are very low for the Eu³⁺ containing glass and for the Tb³⁺ activated glass which contains also lead. A possible explanation could be that lead and europium favour in the glass matrix the formation of a higher concentration of defects with respect to Tb³⁺ doping ions.     

Luminescence and energy transfer in Dy3+/Tb3+ co-doped CaO–Al2O3–B2O3–RE2O3 glass

The new calcium aluminoborate glasses with the composition of CaO–Al₂O₃–B₂O₃–RE₂O₃ (RE = Dy and Tb) were synthesized and the luminescence of Dy³⁺ and Tb³⁺ was investigated. The results show that the emission intensity of Tb³⁺ ion was enhanced when introducing Dy³⁺ ion into CaO–Al₂O₃–B₂O₃–Tb₂O₃ glass due to the energy transfer processes between Dy³⁺ and Tb³⁺. The energy transfer efficiencies, transfer probabilities as well as donor–acceptor critical distances were also calculated. The energy transfer mechanism between Dy³⁺ and Tb³⁺ ions is electric dipole–dipole interaction, which can be concluded by both fluorescence decay and emission intensity ratio varieties.     

Chemical co-precipitation synthesis of luminescent BixY1−xVO4: RE (RE = Eu3+, Dy3+, Er3+) phosphors from hybrid precursors

Using novel synthesis technology, novel luminescent materials of Bi_zY_0.95−xEu_0.05VO₄, Bi_xY_0.97−zDy_0.03VO₄ and Bi_xY_0.98−xEr_0.02VO₄ were prepared. An in situ co-precipitation technology was used to assemble the hybrid precursors. Rare earth coordination polymers with aromatic carboxylic acids were used as the precursors of rare earth oxide components, and polyethylene glycol (PEG) and ammonium vanadate (NH₄VO₃) were composed to assemble inorganic/organic hybrid polymeric dispersing media. Their microstructure and micromorphology have been analyzed by X-ray powder diffraction (XRD) and scanning electronic microscope (SEM). All the emission spectra showed the characteristic absorption of Eu³⁺, Dy³⁺ and Er³⁺, respectively, in the host of YVO₄–BiVO₄.     

Attractive sulfonamide bridging bonds constructing lanthanide centered photoactive covalent hybrids

A new kind of sol–gel derived organic–inorganic hybrid material was prepared for the first time.In this case the organic portion of an acylamine derivation grafted by 3-aminopropyl trimethoxysilane and covalently linked together via sulfonamide linkages. Fourier transform infrared (FTIR), in ultraviolet absorption (UV) spectra and ¹H nuclear magnetic resonance (NMR) spectra were used to confirm these modifications and the X-ray diffraction (XRD) spectra were used to determine the framework. The material’s phosphorescent spectra and luminescence spectra were recorded. An efficient intramolecular energy transfer process between acylamine and lanthanide ions took place within these molecular-based hybrids. Strong green and red emissions were achieved for Tb³⁺ and Sm³⁺ ions, respectively.     

Eu2+/Dy3+ co-doped white light emission glass ceramics under UV light excitation

In the present work, transparent Eu²⁺/Dy³⁺ co-doped white light-emitting glass ceramics containing CaF₂ were successfully prepared under reducing atmosphere. Their luminescence properties have been studied by excitation and emission spectra. A combination of blue, yellow and red emissions has emerged in Eu²⁺/Dy³⁺ co-doped glass and glass ceramics, which allows the observation of bright white light when the samples are excited by the ultraviolet light. Energy transfer (ET) from Eu²⁺ to Dy³⁺ is discovered by directly observing the luminescence intensity of Dy³⁺ in the Eu²⁺/Dy³⁺ co-doped glass which is much stronger than that in the Dy³⁺-doped glass. ET from Eu²⁺ to Dy³⁺ in glass is further confirmed by fluorescence studies performed on the samples with various activator (Dy³⁺) concentrations. The color of luminescence could be adjusted by varying the proportions of europium and dysprosium. The optimal composition generates white light with chromaticity coordinates (0.296, 0.311). The results indicate that Eu²⁺/Dy³⁺ co-doped glass ceramics containing CaF₂ nano-crystals is a potential material for white LED.     

Construction and photoluminescence of amorphous silicone resins containing lanthanide ions as luminescent center

Three series of luminescent silicone resins have been synthesized. This ternary resin (SiPy-La-L, La = Eu, Tb or Dy; L = 1, 10-phenanthroline or acetylacetone) is composed from the precursor, the second ligand and lanthanide ions using a sol–gel method. The precursor is derived from the hydrosilylation reaction of methyldichlorsilane and 4-vinylpyrodine. Lanthanide ions (Eu³⁺, Tb³⁺ and Dy³⁺) act as luminescent center. Structure and texture of silicone resins are characterized by the X-ray diffraction (XRD) and scanning electron microscopy (SEM). The luminescence of silicone resins are monitored and studied in detail. Red and green luminescences are checked when silicone resins are exposed to ultraviolet light, suggesting that the intra-molecular energy-transfer processes take place within these silicone resins.     

Luminescence properties and energy transfer of Eu/Tb ions codoped aluminoborosilicate glasses

Eu/Tb codoped aluminoborosilicate glasses were fabricated by high temperature melting-quenched technique and their luminescence properties were investigated by excitation and emission spectra. Under 376 nm excitation, blue, green and red emission bands were simultaneously observed at 425 nm, 485 nm, 540 nm and 611 nm, respectively. The broad blue emission band centered at 425 nm was originated from the reduced Eu²⁺ ions, which were reduced from Eu³⁺ ions at high temperature in an ambient atmosphere and the reduction process may be related with the optical basicity of glass matrix. A complex bright white light emission was obtained for 0.5 mol% Eu₂O₃, 0.5 mol% Tb₂O₃ codoped aluminoborosilicate glass with CIE-X = 0.31 and CIE-Y = 0.33. The energy transfer among Eu³⁺, Eu²⁺ and Tb³⁺ ions was also discussed.     

Energy transfer from Bi3+ sensitizing the luminescence of Eu3+ in clusters embedded into sol–gel silica glasses

Y³⁺(La³⁺), Eu³⁺ and Bi³⁺ ions co-doped sol–gel silica glasses were synthesized. Photoluminescence spectra show that there is energy transfer from Bi³⁺ ions to the emission band of Eu³⁺ ions. The co-dopants Y³⁺ or La³⁺ have strong effects on the local structure and luminescence of Eu³⁺ ions. For 0.5 mol% Eu³⁺ ions doped glasses, the co-doping of 1 mol% Bi³⁺ and 1 mol% Y³⁺ is the most appropriate for the sensitization from Bi³⁺ to Eu³⁺. The sensitization effectiveness from Bi³⁺ ions to Eu³⁺ ions was studied by changing the amount of Bi³⁺ and Y³⁺, and clusters containing rare earth ions and Bi³⁺ ions dominate the energy transfer processes. The comparison of luminescent R-values (the intensity ratio of ⁵D₀ → ⁷F₂/⁵D₀ → ⁷F₁ in Eu³⁺ ions) between glasses containing La³⁺ and containing Y³⁺ verifies the formation of clusters in sol–gel glasses. As a favorable configuration for energy transfer, the accurate design and synthesis of clusters-contained glasses may provide a new kind of luminescent materials.     

Lanthanide molecular-based hybrids covalently bonded with silica: Photoluminescence and control of micromorphology

The syntheses of modified 5-bromonicotinic acid by (3-aminopropyl)triethoxysilane and the preparation of their corresponding organic–inorganic molecular-based hybrid material with the two components equipped with covalent bonds are described. The organic moiety is a derivative of 5-bromonicotinic acid which is applied to coordinate to RE³⁺ and further introduced into silica matrices by Si–O bonds after hydrolysis and polycondensation processes. Judd–Ofelt theory proves that covalency increases along with increasing reciprocal energy difference between the 4fN and 4fN-15d1configurations. Ultraviolet absorption, phosphorescence and luminescence spectra were utilized to characterize the photophysical properties of the obtained hybrid material and the above spectroscopic data reveal that the triplet energy of modified 5-bromonicotinic acid matches with the emissive energy level of RE³⁺. In this way, the intramolecular energy transfer process took place within these molecular-based hybrids and strong green, red or blue emissions of RE³⁺ have been acquired. Scanning electronic microscope presents no phase separation phenomenon appear and the different crystal structures of lanthanide complex precursor molecules have influence on the microstructure and micromorphology of corresponding molecular hybrids.     

Novel luminescence behaviors of Ce3+/Tb3+ co-doped phosphate glasses

In the present work, Ce³⁺/Tb³⁺ co-doped 60P₂O₅-30BaO-10B₂O₃ phosphate glasses are prepared and their luminescence properties are presented. Under excitation at 303 nm, the Ce³⁺ ions singly doped sample show a novel red emission besides the UV one. The co-doped samples show enhanced Tb³⁺ ions emission with the increasing of Tb³⁺ ions concentration at the cost of Ce³⁺ emission. The mechanism of this luminescent behavior is discussed with respect to the relevant energy transfer process.     

Intense luminescence of amorphous Eu2O3 prepared by aqueous sol–gel method

Amorphous Eu₂O₃ was prepared by an aqueous sol–gel method. Emission due to the ⁵D₀ → ⁷F_J (J = 0, 1, 2) transitions of Eu³⁺ ions were observed. The dominant transition was the ⁵D₀ → ⁷F₂ red emission of Eu³⁺. The properties of the as-prepared samples were different with changes in the annealing temperature. To investigate the luminescence properties of the amorphous Eu₂O₃, the temperature-dependent photoluminescence (PL) spectra of samples annealed at 600 °C were measured in the temperature range 77–300 K. PL peak positions were unchanged with the change of temperature.     

White light emission from Eu3 +/Tb3 +/Tm3 + triply-doped aluminoborate glass excited by UV light

The Eu^3 +/Tb^3 +/Tm^3 + triply-doped glasses with the composition of CaO―Al₂O₃―B₂O₃―RE₂O₃ (RE = Eu,Tb,Tm) have been synthesized by melt quenching method. The photoluminescence of these Eu^3 +/Tb^3 +/Tm^3 + triply-doped glasses (CaAlB:RE^3 +) were studied and the emission spectra combining with blue, green and reddish orange bands were observed. Under 360 nm wavelength excitation the white light emission is achieved when the concentration (x) of Tm^3 + in Ca_0.931 ?xAlB:Eu^3 +_0.038,Tb^3 +_0.031,Tm^3 +_x glass is in the range of 0.0013-0.011 per mol matrix. In addition, the energy transfer (ET) between Tb^3 + and Eu^3 + ions in Eu^3 +/Tb^3 +/Tm^3 + triply-doped glasses was validated and the electric dipole–dipole interaction is responsible for the ET process of Tb^3 + → Eu^3 + at low concentrations. Hence, the Eu^3 +/Tb^3 +/Tm^3 + triply-doped aluminoborate glass could be a potential candidate for white LEDs.     

Synthesis and Luminescence Characteristics of LiMgAlF6:Ln3+ (Ln = Ce,Eu, Tb)

By solid state reaction, LiMgAlF₆ and LiMgAlF₆: Ln³⁺ are synthetized with the ratio 120/100/110 of LiF/MgF₂/AlF₃, at 1008 K, in high-purity Ar stream. Their crystal structure which belongs to hexagonal system are determined by X-Ray-Diffraction (XRD). Luminescence characteristics of Ce³⁺, Eu³⁺, Tb³⁺ and sensitization of Ce³⁺ to Tb³⁺ in LiMgAlF₆ are studied. It is shown that the sensitization of Ce³⁺ to Tb³⁺ is efficient and a bright green emission is observed.     

Impurity-trapped excitons: Experimental evidence and theoretical concept

The paper summarizes experimental evidence of anomalous luminescence in RE-doped dielectric materials. Special attention is paid to Pr³⁺-doped LiNbO₃ and LiTaO₃, and Eu²⁺-doped XF_2, where X = Ba, Sr. Luminescence, luminescence excitation spectra and luminescence kinetics results are discussed obtained at ambient and high hydrostatic pressure at various temperatures. Hydrostatic pressure has been shown to cause a red shift of anomalous luminescence. The experimental data show the existence of temperature- and pressure-induced spectral transformation where anomalous luminescence is replaced with normal d–f emission in Eu²⁺ centers. The model predicts strong electron-lattice coupling of bound excitons and relaxation in the system’s excited states, as well as the pressure effect of spectral transformation from anomalous to normal emission.