Synthesis and optical characterizations of undoped and rare-earth-doped CaF2 nanoparticles

The synthesis of undoped as well as Yb or Er-doped CaF₂ nanocrystals using a reverse micelle method is reported. X-ray powder diffraction and transmission electron microscopy analysis showed that the products were single phased and rather monodispersed with an average particles size around 20 nm. The emission spectra and fluorescence decay times of both Yb³⁺ and Er³⁺ rare earths (RE) ions in CaF₂ nanoparticles are presented. The particles size is increased by heating the as-obtained nanoparticles at different temperatures. The effect of annealing on the optical properties of the two RE ions in CaF₂ is also investigated.     

Zn selective luminescent ‘off-on’ probes derived from diaryl oxadiazole and aza-15-crown-5

New photo-induced electron transfer (PET) probes OMOX and OBOX, carrying an additional binding site in the form of ‘oxadiazole nitrogen’ have been designed to evaluate binding interactions with biologically significant Li⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺, and Zn²⁺ including environmentally toxic Ba²⁺ and Cd²⁺ using optical spectral techniques. While Li⁺, Na⁺, and K⁺ did not appreciably perturb either the absorption or emission spectra, Ba²⁺, Ca²⁺, Mg²⁺, Zn²⁺, and Cd²⁺ induced slight red shifts (2-8 nm) in the UV-visible spectra as well as pronounced chelation induced enhanced fluorescence (CHEF). Both OMOX and OBOX exhibited the highest CHEF in contact with the zinc ion, whereas Ba²⁺, Ca²⁺, Mg²⁺, and Cd²⁺ induced relatively less emission enhancements. OBOX, which is a poorer emitter (Φ_f=0.0062) than OMOX (Φ_f=0.015), showed highly promising 160-fold emission enhancement in the presence of Zn²⁺. Potential, therefore is available in OBOX to function as a selective luminescent ‘off-on’ sensor for Zn²⁺ in the presence of coordinatively competing Ba²⁺, Ca²⁺, Mg²⁺, and Cd²⁺ ions.     

Enhanced quantum yield of yellow photoluminescence of Dy ions in nonlinear optical Ba2TiSi2O8 nanocrystals formed in glass

Transparent crystallized glasses consisting of nonlinear optical Ba₂TiSi₂O₈ nanocrystals (diameter: ∼100 nm) are prepared through the crystallization of 40BaO-20TiO₂-40SiO₂-0.5Dy₂O₃ glass (in the molar ratio), and photoluminescence quantum yields of Dy³⁺ ions in the visible region are evaluated directly by using a photoluminescence spectrometer with an integrating sphere. The incorporation of Dy³⁺ ions into Ba₂TiSi₂O₈ nanocrystals is confirmed from the X-ray diffraction analyses. The total quantum yields of the emissions at the bands of ⁴F_9/2→⁶H_15/2 (blue: 484 nm), ⁴F_9/2→⁶H_13/2 (yellow: 575 nm), and ⁴F_9/2→⁶H_11/2 (red: 669 nm) in the crystallized glasses are ∼15%, being about four times larger compared with the precursor glass. It is found that the intensity of yellow (575 nm) emissions and the branching ratio of the yellow (575 nm)/blue (484 nm) intensity ratio increase largely due to the crystallization. It is suggested from Judd-Ofelt analyses that the site symmetry of Dy³⁺ ions in the crystallized glasses is largely distorted, giving a large increase in the yellow emissions. It is proposed that Dy³⁺ ions substitute Ba²⁺ sites in Ba₂TiSi₂O₈ nanocrystals.     

Tunable photoluminescence of NaYF4:Eu nanocrystals by Sr codoping

NaYF₄:Eu/Sr nanocrystals were synthesized by a hydrothermal method. Tunable photoluminescence of the NaYF₄:Eu nanocrystals was successfully achieved by codoping with Sr²⁺ ions. With increasing Sr²⁺ concentration, not only the X-ray diffraction peaks of the nanocrystals become broader, but also the positions of them shift toward larger lattice parameters. Eu³⁺ and Eu²⁺ have been found to coexist in an NaYF₄:Eu/Sr. The Eu³⁺/Eu²⁺ emission intensity ratio changed with the Sr²⁺ concentration and excitation wavelength. More interestingly, the spectral configurations of Eu²⁺ and Eu³⁺ also varied with the excitation wavelength, indicating that the nanocrystals have multiple luminescence centers or emitting states.     

Uniform Ln (Eu, Tb) doped NaLa(WO4)2 nanocrystals: Synthesis, characterization, and optical properties

Uniform shuttle-like Ln³⁺ (Eu³⁺, Tb³⁺) doped NaLa(WO₄)₂ nanocrystals have been solvothermally synthesized, and the size of the nanocrystals could be easily controlled by adjusting the volume ratio of ethylene glycol (EG) to water. Doped with 5 mol% Eu³⁺ and Tb³⁺ ions, the NaLa(WO₄)₂ nanocrystals showed strong red and green emissions with lifetimes of 0.8 and 1.40 ms, respectively. A high quenching concentration of 15 mol% was observed in Eu³⁺-doped NaLa(WO₄)₂ nanocrystals and 35 mol% in Tb³⁺-doped NaLa(WO₄)₂ nanocrystals. The emission intensity measurements of Eu³⁺-doped NaLa(WO₄)₂ with different sizes indicated that the emission intensity of shuttles with length of 300 nm in average was stronger than that of shuttles with length of 900 nm in average, but was weaker than that of needles with length of 4 and 9 μm in average.     

Luminescence and vibrational spectra of Ba5Li2W3O15

The infrared and Raman spectra of Ba₅Li₂W₃O₁₅ are reported down to 200 cm^?1. From the internal stretching modes of the tungstate octahedra the crystallographic order between lithium and tungsten in the face-sharing octahedra can be derived. The green tungstate luminescence shows a low quenching temperature that is described with the Dexter-Klick-Russell model. The U⁶⁺ ion shows a yellow emission in Ba₅Li₂W₃O₁₅. There is ample evidence for two different U⁶⁺ centers with different decay times (10 and 80 μsec) and different emission and excitation spectra. One of these is located in a single layer of tungstate octahedra, the other in a double layer of octahedra.     

(Ca,Me)La4Si3O13:Eu3+(Me=Sr,Ba)荧光粉的结构和发光特性

采用高温固相法制备了(Ca,Me)La4Si3O13∶Eu3+(Me=Sr,Ba)系列红色荧光体,考察了Eu3+掺杂浓度和Sr2+,Ba2+置换对荧光体结构和发光特性的影响。Eu3+最佳掺杂浓度为nEu3+∶nLa3+=1∶7,5D0-7F2与5D0-7F1跃迁发射强度比为2.55。Eu3+掺杂使晶胞参数a和c呈线性变小,对c的影响大于a,使a/c比增大。Sr2+和Ba2+分别置换基质中的Ca2+可以形成完全固溶体,晶胞参数随Sr2+或Ba2+的置换量增加呈线性增大,使a/c比减小。各发射峰强度在Sr2+置换量为0.4 mol时出现极大值,但随Ba2+置换量的增加而不断增强,全置换后荧光强度最大。荧光体的色坐标为(0.638 5,0.353 0)。     

Crystal structure of Eu-doped M3MgSi2O8 (M: Ba, Sr, Ca) compounds and their emission properties

Emission properties of Eu²⁺-doped M₃MgSi₂O₈ (M: Ba, Sr, Ca) are discussed in terms of the crystal structure. When Ba²⁺ ions account for over one third of M²⁺ ions, M₃MgSi₂O₈ crystallizes in glaserite-type trigonal structure, while Ba-free compounds crystallize in merwinite-type monoclinic structure. Under UV excitation, the Eu²⁺-doped glaserite-type compounds exhibit an intense blue emission assigned to 5d-4f electron transition at about 435 nm, regardless of the molar ratio of Ba²⁺, Sr²⁺ and Ca²⁺ ions. By contrast, the Eu²⁺-doped merwinite-type compounds show an emission color sensitive to the ratio. A detailed analysis of the emission spectra reveals that the emission chromaticity for the Eu²⁺-doped M₃MgSi₂O₈ is composed of two emission peaks reflecting two different sites accommodating M²⁺ ion.     

New PCT probes featuring N-phenylmonoaza-18-crown-6 and aryl/pyridyl oxadiazoles: optical spectral studies of solvent effects and selected metal ions

Aryl/pyridyl oxadiazole chromophores 6, 8 and 10, carrying N-phenyl aza-18-crown-6 have been synthesized as new photo-induced charge transfer (PCT) probes. While, the absorption spectra of the hosts experienced a slight negative solvatochromism, however the emission bands were dramatically red shifted (Stokes shifts up to 178 nm) in solvents of increasing polarity. Among the metal ions tested, Li⁺, Na⁺, K⁺ and Mg²⁺ did not appreciably perturbed the optical properties of the hosts. On the other hand, Ba²⁺ and to a lesser extent Ca²⁺ induced marked blue shifts in both the absorption and emission spectra of the hosts. The magnitude of cation induced spectral blue shifts corresponded with the increasing acceptor strength of the attached aryl/pyridyl groups in the host molecules. The blue shifts and the stability constants were found to follow the order Ba²⁺ > Ca²⁺ ? Mg²⁺ > Na⁺ > Li⁺ > K⁺. Competitive experiments performed with a matrix of ions also revealed superior binding affinity of Ba²⁺ with all the hosts examined. Noteworthily, the deep yellow solution (λ_max, 386 nm) of the host 10 was completely bleached (λ_max, 320 nm), in the company of Ba²⁺ thereby allowing the naked eye detection of this ion.     

Up/downconversion luminescence rare-earth ion-doped Y2O3 1D nanocrystals

Multicolor luminescent rare-earth ion-doped Y2O3 nanocrystals(NCs) were prepared by a solvethermal method.The as-synthesized NCs yielded nanosheets,nanowires(NWs) and nanorods(NRs) with the increase of alkali(NaOH) in oleic acid system.Moreover,Y2O3 nanowires with controllable size have also been obtained.After sintering,the PL intensity of Y2O3:Ln 3+ nanocrystals increased with the changed morphology of the precursor,that is,Y(OH) 3 nanocrystals.Both downconversion(red emission for Y2O3:Eu 3+ and green emission for Y2O3:Tb 3+) and upconversion(red emission for Y2O3:Yb/Er 3+) luminescence of the as-prepared nanocrystals have been demonstrated in this work.We also found that the PL intensity of Y2O3:Ln 3+ NCs dispersed in polar solvent was stronger than that in nonpolar solvent.Their up/downconversion fluorescence and controllable morphology might promise further fundamental research and biochemistry such as nanoscale optoelectronics,nanolasers,and ultrasensitive multicolor biolables.     

Enhanced photoluminescence of Ba2GdNbO6: Eu/Dy phosphors by Li doping

The Ba₂GdNbO₆: Eu³⁺/Dy³⁺ and Li⁺-doped Ba₂GdNbO₆: Eu³⁺/Dy³⁺ phosphors were prepared by solid-state reaction process. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and photoluminescence (PL) as well as lifetimes, was utilized to characterize the resulting phosphors. Under the excitation of ultraviolet light, the Ba₂GdNbO₆: Eu³⁺/Dy³⁺ and Li⁺-doped Ba₂GdNbO₆: Eu³⁺/Dy³⁺ show the characteristic emissions of Eu³⁺ (⁵D₀-⁷F_1,2,3 transitions dominated by ⁵D₀-⁷F₁ at 593 nm) and Dy³⁺ (⁴F_9/2-⁶H_15/2,_13/2 transitions dominated by ⁴F_9/2-⁶H_15/2 at 494 nm), respectively. The incorporation of Li⁺ ions into the Ba₂GdNbO₆: Eu³⁺/Dy³⁺ phosphors has enhanced the PL intensities depending on the doping concentration of Li⁺, and the highest emission was obtained in Ba₂Gd_0.9NbO₆: 0.10Eu³⁺, 0.01Li⁺ and Ba₂Gd_0.95NbO₆: 0.05Dy³⁺, 0.07Li⁺, respectively. An energy level diagram was proposed to explain the luminescence process in the phosphors.     

Controllable Multicolor Upconversion Luminescence by Tuning the NaF Dosage

Multicolor upconversion (UC) luminescence of NaYF₄:Yb³⁺/Er³⁺ nanoparticles (NPs) was successfully tuned by simply controlling the NaF dosage. Unlike UC nanocrystals previously reported in the literature with multicolor emission obtained by varying the rare‐earth dopants, the current work developed a new approach to tune the UC emission color by controlling the NaF concentration without changing the ratio and dosage of rare‐earth ions. TEM and powder XRD were used to characterize the shape, size, and composition of the UC luminescent nanocrystals. The luminescence images, emission spectra, and multicolor emission mechanism of the NPs have also been demonstrated. As a result of the excellent ability of this new method to manipulate color emission, this will open up new avenues in the areas of bioprobes, light‐emitting devices, color displays, lasers, and so forth. To demonstrate their biological applications, the water‐stable, biocompatible, and bioconjugatable NaYF₄:Yb³⁺/Er³⁺@poly(acrylic acid) NPs were synthesized by this developed strategy and applied in targeted‐cell UC luminescence imaging.     

Synthesis and Infrared Multi‐band Absorption Properties of Core‐shell NaYF4:Yb3+, Er3+@SiO2 Nanoparticles

Due to the unique size effects, nanomaterials in infrared absorption have attracted much attention for their strong absorption in the infrared region. To achieve the infrared multi‐band absorption, we propose to synthesize a core‐shell structure nanomaterial consisting of NaYF₄:Yb³⁺, Er³⁺ core and a layer of SiO₂ as shell. A series of NaYF₄:Yb³⁺, Er³⁺ nanocrystals were synthesized through hydrothermal method by adjusting the ratio of citric acid(CA)‐to‐NaOH, and the effects of CA concentration, and NaOH concentration were studied in detail. NaYF₄:Yb³⁺, Er³⁺@SiO₂ nanoparticles were synthesized by sol‐gel method using TEOS as silica source. The results show that the core‐shell NaYF₄:Yb³⁺, Er³⁺@SiO₂ nanoparticles were successfully synthesized. Up‐conversion spectra of these nanoparticles were recorded with 980 nm laser excitation under room temperature. There are no changes of the emission centers of nanoparticles before or after silica coating, but the emission intensities of nanoparticles after silica coating are weakened. Furthermore, the property of infrared multi‐band absorption was tested through ultraviolet‐visible‐near infrared spectrophotometer and infrared absorption spectra. The results illustrate that the multi‐band infrared absorption nanomaterial was successfully synthesized.     

Synthesis of highly fluorescent LaF3:Ln/LaF3 core/shell nanocrystals by a surfactant-free aqueous solution route

A surfactant-free aqueous solution route has been established for the synthesis of LaF₃:Ln³⁺/LaF₃ core/shell nanocrystals (Ln=Ce, Tb, Nd) heated at 75 °C at ambient pressure. All the as-prepared nanocrystals with spherical shape have an average size around 20 nm, and consist of well crystallized hexagonal phases. The X-ray photoelectron spectra was used to confirm that the LaF₃ shells have coated the LaF₃:Ce³⁺, Tb³⁺ cores. Compared with that of the original cores under the same conditions, the emission intensity of the LaF₃:Ce³⁺, Tb³⁺/LaF₃ and LaF₃:Nd³⁺/LaF₃ core/shell nanocrystals increased significantly of 120% and 60%, respectively. The quantum yield of the LaF₃:Ce³⁺, Tb³⁺/LaF₃ core/shell nanocrystals reached about 27% in aqueous solution. These results indicate that a significant reduction of the quenching from the surface of the core nanocrystals can be obtained by the synthesis of the core/shell structures, and this method can provide more desirable lanthanide-doped nanocrystals for potential biological applications.     

明胶溶液中针状纳米HgS的仿生合成

以明胶为模板剂,制备出在明胶水溶液中稳定存在的HgS微晶.通过扫描电镜(SEM)图像表明,生长时间为2d的样品为微晶结构,生长15d的HgS微晶为针状,平均直径约87nm,长度约1.3μm.紫外可见吸收和荧光光谱的测试结果表明,所合成HgS具有量子限域效应.明胶分子的构象变化对HgS纳米颗粒的成核和形貌转化起到非常重要的作用.     

Conductometric and microcalorimetric analysis of the alkaline-earth/alkali-metal ion exchange onto polyacrylic acid

The specificity of the exchange between divalent (Di²⁺ = Ca²⁺ or Ba²⁺) and monovalent (M⁺ = Li⁺, Na⁺ or K⁺) ions onto a polyacrylic chain is examined using conductometric and microcalorimetric techniques. Assuming the formation of a bidentate complex between the Di²⁺ and the carboxylate groups, the conductometric data give the exchange ratio (Di²⁺/M⁺) and the speciation of the acrylic groups. No significant difference is observed between the three alkali-metal ions for a given Di²⁺ ion. Comparisons between Ca²⁺ and Ba²⁺ show a stronger hydrophobicity of the former as it precipitates at a complexation ratio r = 0.33 versus r = 0.45 for the Ba²⁺ salt. Microcalorimetric data show that all Di²⁺/M⁺ exchange energies are positive and depend significantly on the type of cations. The largest displacement energy (the more positive) is found for the binding of Ca²⁺ with sodium polyacrylate (8.13 kJ · mol⁻¹) and the smallest for Ba²⁺ with lithium polyacrylate (1.88 kJ · mol⁻¹). The interpretation of the data leads to the conclusion that specificity of the Di²⁺ binding originates in the dehydration phenomenon and specificity between the three alkali-metal ions is due to the decrease in the electrostatic bond strength with an increase in the ionic radii. The Di²⁺/M⁺ exchange is entropically driven. Received: 28 January 1999 Accepted in revised form: 7 April 1999     

Luminescence enhancement of Eu, Ce co-doped Ba3Si5O13−δNδ phosphors

Host lattice Ba₃Si₅O_13−δN_δ oxonitridosilicates have been synthesized by the traditional solid state reaction method. The lattice structure is based on layers of vertex-linked SiO₄ tetrahedrons and Ba²⁺ ions, where each Ba²⁺ ion is coordinated by eight oxygen atoms forming distorted square antiprisms. Under an excitation wavelength of 365 nm, Ba₃Si₅O_13−δN_δ:Eu²⁺ and Ba₃Si₅O_13−δN_δ:Eu²⁺,Ce³⁺ show broad emission bands from about 400-620 nm, with maxima at about 480 nm and half-peak width of around 130 nm. The emission intensity is strongly enhanced by co-doping Ce³⁺ ions into the Ba₃Si₅O_13−δN_δ:Eu²⁺ phosphor, which could be explained by energy transfer. The excitation band from the near UV to the blue light region confirms the possibility that Ba₃Si₅O_13−δN_δ:Eu²⁺, Ce³⁺ could be used as a phosphor for white LEDs.     

Combinatorial Optimization of Ba/Fe-cordierite Solid Solution (Ba0.05Fe0.1Mg)2Al4Si5O18 for High Infrared Radiance Materials

A combinatorial chemistry method was employed to screen the Ba²⁺ and Fe³⁺ incorporated into cordierite structure (Ba_0.05Fe_0.1Mg)₂Al₄Si₅O₁₈ for exploring of high infrared radiance materials. A series of square-type sample array that consists of 7×7 compositions was syn-thesized by ink-jetting nitrate solutions into micro-reactor wells in a ceramic plate and then heat-treated at high temperatures. X-ray diffraction and infrared thermograph were used to analyze the effects of Ba²⁺/Fe³⁺ incorporating on the lattice distortion of cordierite and resultant changes in infrared radiance properties. Based on the results of X-ray phase analy-sis and radiance measurement of the scale-up prepared samples, the optimal Ba²⁺ and Fe³⁺ co-adding amount was determined to be 5%Ba²⁺ plus 10%Fe³⁺. Moreover, the infrared emissivity of the optimal composition at 100 oC was found to be higher than 0.8 in a wide wavelength range of 5-24 μm. The research work demonstrates a promising application of Ba²⁺/Fe³⁺ cordierite solid solution as a kind of infrared heating materials for energy saving.     

Voltammetric study of metal ions binding by biindolizine heterocyclophanes and their acyclic analogues

The binding of ions Li⁺, Na⁺, K⁺, (group I), Mg²⁺, Al³⁺, Ga³⁺ (group II), Ca²⁺, Pb²⁺ (group III) ions, Ba²⁺ and paraquat by heterocyclophanes containing biindolizine and quinoxaline fragments connected by 3,6,9-trioxaundecane and 5,8,11,14,17-pentaoxageneicosane spacers, and also their acyclic analogues, in the acetonitrile-0.1 M Bu₄NBF₄ is studied by cyclic voltammetry. A conclusion is drawn that the ions of the group I are not bound by these compounds; the paraquat is not bound by heterocyclophane with the 5,8,11,14,17-pentaoxageneicosan spacers. For ions of the group II, reversible redox-switchable binding by the macrocycles with the 3,6,9-trioxaundecane and 5,8,11,14,17-pentaoxageneicosan spacers is observed: the initial compounds show the binding; their radical cations and dications do not. The binding of the ions of the group III and Ba²⁺ is determined by the macrocycles’ size. In particular, these ions are bound not only by the heterocyclophane with 3,6,9-trioxaundecane spacers but also by its radical cation or dication. The binding results in the corresponding dication stabilization. The heterocyclophane with the 5,8,11,14,17-pentaoxageneicosan spacers demonstrates the redox-switchable binding of Ca²⁺ and Pb²⁺ ions; no effect of Ba²⁺ ions on the cyclic voltammograms of this heterocyclophane was observed. In the ternary system “heterocyclophane with 3,6,9-trioxaundecane spacers + ions of the group II (Al³⁺, Ga³⁺) + ions of the group III (Ca²⁺, Pb²⁺)” either primary binding of the group III ion Pb2+ or concurrent binding of the ions of the group II and the group III, with the system’s reversible redox-switching from one metal complex to another, was observed.     

Diethyl (biscyclohexano)BODIPY dicarboxylates. Chelation of alkaline-earth metal ions and sensor properties

meso-Aryl-substituted (biscyclohexano)bis(ethoxycarbonyl)BODIPY [aryl = phenyl, 3,4-dimethoxyphenyl, and 2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13-benzopentaoxacyclopentadecin-15-yl-(m-{benzo-15-crown-5}-yl)] were synthesized. The effect of alkaline-earth metals on the absorption and fluorescence spectra of these compounds was investigated. In all compounds along with the mechanism of the photoinduced electron transfer (PET), well-known for the crown-containing BODIPY-based sensors, one more response pattern is observed. The large excess of Ca²⁺ and Ba²⁺ ions in the system leads to the changes both in the UV-Vis and emission spectra. The complex formation results in the decrease of emission intensity and in its red shift. Besides, a new longwave absorption band appears in the UV-Vis spectrum of the BODIPY-metal ion complex. The formation constants of the complexes corresponding to this response pattern is about 100 times less than the formation constant of Ca²⁺-crown ether complex. ¹H, ¹³C, ¹¹B, and ¹⁹F NMR spectra, the results of quantum-chemical calculations, and their comparison with the literature data of X-ray diffraction study suggest that the binding of Ca²⁺ and Ba²⁺ ions occurs in the cavity formed by the fluorine atoms and the carbonyl oxygen atoms of the ester groups.