Dissociation pathways of doubly and triply charged gold clusters

Collision induced dissociation is applied to study the fragmentation channels of multiply charged gold clusters, Au N2⁺, size N= 7 –35, and Au> _N3+}, N = 19–35, stored in an ion cyclotron resonance (Penning) trap. The main dissociation pathways are neutral monomer evaporation, Au> _NZ+to Au> _N-1Z+} + Au, for the larger and fission into a charged trimer plus the remaining cluster, Au> _NZ+to{}Au> _N-3(Z-1)+} +{}Au> ₃₊}, for the smaller clusters. In the intermediate cluster size region an odd–even alternation of the two competing decay pathways is observed. In addition, for some specific cluster sizes there are indications of neutral dimer evaporation, Au> _NZ+to{}Au> _N-2Z++Au> ₂}, and of extremely asymmetric fission of the form Au> _NZ+to Au> _N-1(Z-1)+} + Au⁺. This revised version was published online in July 2006 with corrections to the Cover Date.     

Defect Structure and Up-conversion Luminescence Properties of ZrO<Subscript>2</Subscript>:Yb<Superscript>3+</Superscript>,Er<Superscript>3+</Superscript> Nanomaterials

The up-converting ZrO₂:Yb³⁺,Er³⁺ nanomaterials were prepared with the combustion and sol–gel methods. FT-IR spectroscopy was used for analyzing the impurities. The crystal structures were characterized with X-ray powder diffraction and the mean crystallite sizes were estimated with the Scherrer formula. Up-conversion luminescence measurements were made at room temperature with IR-laser excitation at 977 nm. The IR spectra revealed the conventional and OH⁻ impurities for the combustion synthesis products. The structure of the ZrO₂:Yb³⁺, Er³⁺ nanomaterials was cubic except for the minor monoclinic and tetragonal impurities obtained with the sol–gel method. The materials showed red (650–700 nm) and green (520–560 nm) up-conversion luminescence due to the ⁴F_9/2→⁴I_15/2 and (²H_11/2, ⁴S_3/2)→⁴I_15/2 transitions of Er³⁺, respectively. The products obtained with the combustion synthesis exhibited the most intense luminescence intensity and showed considerable afterglow.     

A Novel Hg<Superscript>2+</Superscript> Selective Ratiometric Fluorescent Chemodosimeter Based on an Intramolecular FRET Mechanism

A irreversible Hg²⁺ selective ratiometric fluorescence probe FR, a fluorescein fluorophore linked to a rhodamine B hydrazide by a thiourea spacer, was designed and synthesized. The developed probe FR exhibited great ratiometric fluorescence enhancement and remarkable yellow-magenta color change toward Hg²⁺ with excellent selectivity in aqueous acetone solution, and the ratiometric fluorescence response to Hg²⁺ was not interfered by other metal cations including Fe³⁺, Co²⁺, Ni²⁺, Cr³⁺, Zn²⁺, Pb²⁺, Cd²⁺, Ca²⁺, Mg²⁺, Ba²⁺ and Mn²⁺. The linear range and the detection limit of this supposed ratiometric fluorescence method for Hg²⁺ were 0.0–10.0 × 10⁻⁶ and 5 × 10⁻⁸ M, respectively.     

Ferromagnetic Interaction between Copper and Terbium Ions in Pentanuclear Cluster [Cu3Tb2(ClCH2COO)12(H2O)8] · 2H2O

For the first time the exchange interaction between copper and non-Kramers Tb³⁺ ions was studied by means of electron paramagnetic resonance (EPR). Features of the manifestation of this interaction in the EPR spectra of dimer fragments Cu–Tb and pentanuclear fragments Cu–Tb–Cu–Tb–Cu are analyzed. The possibility to determine the sign and value of this interaction from EPR spectra for the case when the lowest states of Tb³⁺ are the states |0〉, | ± 1〉 is shown. The exchange interaction between copper and trivalent terbium ions in the studied pentanuclear complex is ferromagnetic. Authors' address: Violeta K. Voronkova, Kazan Physical-Technical Institute, Russian Academy of Sciences, Sibirsky trakt 10/7, Kazan 420029, Russian Federation     

Design and Synthesis of Highly Photostable Yellow–Green Emitting 1,8-Naphthalimides as Fluorescent Sensors for Metal Cations and Protons

Two highly photostable yellow–green emitting 1,8-naphthalimides 5 and 6, containing both N-linked hindered amine moiety and a secondary or tertiary cation receptor, were synthesized for the first time. Novel compounds were configured as “fluorophore–spacer–receptor” systems based on photoinduced electron transfer. Photophysical characteristics of the dyes were investigated in DMF and water/DMF (4:1, v/v) solution. The ability of the new compounds to detect cations was evaluated by the changes in their fluorescence intensity in the presence of metal ions (Cu²⁺, Pb²⁺, Zn²⁺, Ni²⁺, Co²⁺) and protons. The presence of metal ions and protons was found to disallow a photoinduced electron transfer leading to an enhancement in the dye fluorescence intensity. Compound 5, containing secondary amine receptor, displayed a good sensor activity towards metal ions and protons. However the sensor activity of dye 6, containing a tertiary amine receptor and a shorter hydrocarbon spacer, was substantially higher. The results obtained indicate the potential of the novel compounds as highly photostable and efficient “off–on” pH switchers and fluorescent detectors for metal ions with pronounced selectivity towards Cu²⁺ ions.     

Energy transfer from the host to Er<Superscript>3+</Superscript> dopants in semiconductor SnO<Subscript>2</Subscript> nanocrystals segregated in sol–gel silica glasses

Undoped and Er³⁺-doped glass–ceramics of composition (100−x)SiO₂–xSnO₂, with x = 5 or 10 and with 0.4 or 0.8 mol% of Er³⁺ ions, were synthesised by thermal treatment of precursor sol–gel glasses. Structural studies were developed by X-Ray Diffraction. Wide band gap SnO₂ semiconductor quantum-dots embedded in the insulator SiO₂ glass are obtained. The mean radius of the SnO₂ nanocrystals, ranging from 2 to 3.2 nm, is comparable to the exciton Bohr radius. The luminescence properties have been analysed as a function of sample composition and thermal treatment. The results show that Er³⁺ ions are partially partitioned into the nanocrystalline phase. An efficient UV excitation of the Er³⁺ ions by energy transfer from the SnO₂ nanocrystal host is observed. The Er³⁺ ions located in the SnO₂ nanocrystals are selectively excited by this energy transfer mechanism. On the other hand, emission from the Er³⁺ ions remaining in the silica glassy phase is obtained by direct excitation of these ions.     

Magnetic properties of LiNi<Subscript>0.5</Subscript>Mn<Subscript>0.47</Subscript>Al<Subscript>0.03</Subscript>O<Subscript>2</Subscript> as positive electrode for Li-ion batteries

The layered LiNi_0.5Mn_0.47Al_0.03O₂ was synthesized by wet chemical method and characterized by X-ray diffraction and analysis of magnetic measurements. The powders adopted the α-NaFeO₂ structure. This substitution of Al for Mn promotes the formation of Li(Ni_0.47²⁺Ni_0.03³⁺Mn_0.47⁴⁺Al_0.03³⁺)O₂ structures and induces an increase in the average oxidation state of Ni, thereby leading to the shrinkage of the lattice unit cell. The concentration of antisite defects in which Ni²⁺ occupies the (3a) Li lattice sites in the Wyckoff notation has been estimated from the ferromagnetic Ni²⁺(3a)–Mn⁴⁺(3b) pairing observed below 140 K. The substitution of 3% Al for Mn reduces the amount of antisite defects from 7% to 6.4–6.5%. The analysis of the magnetic properties in the paramagnetic phase in the framework of the Curie–Weiss law agrees well with the combination of Ni²⁺ (S = 1), Ni³⁺ (S = 1/2) and Mn⁴⁺ (S = 3/2) spin-only values. Delithiation has been made by the use of K₂S₂O₈. According to this process, known to be softer than the electrochemical one, the nickel ions in the (3b) sites are converted into Ni⁴⁺ in the high spin configuration, while Ni²⁺(3a)–Mn⁴⁺(3b) ferromagnetic pairs remain, as the Li⁺(3b) ions linked to the Ni²⁺(3a) ions in the antisite defects are not removed. The results show that the antisite defect is surrounded by Mn⁴⁺ ions, implying the nonuniform distribution of the cations in agreement with previous NMR and neutron experiments.     

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.     

Luminescence characteristics of energy transfer between Ce<Superscript>3+</Superscript> and Eu<Superscript>2+</Superscript> in NaMgPO<Subscript>4</Subscript> phosphor

Powder samples of NaMgPO₄ doped with Eu²⁺ and Ce³⁺ were prepared and their photoluminescence spectra were systemically studied. Energy transfer from Ce³⁺ to Eu²⁺ in NaMgPO₄ phosphor was observed by investigating the optical properties from photoluminescence spectra in Eu²⁺ or Ce³⁺ singly doped and Eu²⁺–Ce³⁺ codoped sodium magnesium orthophosphates, NaMgPO₄. The enhancement of UV excitation is attributed to energy transfer from Ce³⁺ to Eu²⁺, and Ce³⁺ plays a role as a sensitizer. Ce³⁺–Eu²⁺ codoped NaMgPO₄ phosphors in which Eu²⁺ can be efficiently excited by 390 nm are potential candidates for phosphor-converted LEDs.     

The rate constants of singlet oxygen collision-induced emission at 634 and 703 nm wavelengths

Absolute spectral luminosity from an O₂–O₂(a)-H₂O gas flow formed by a chemical singlet oxygen generator was measured at 600–800 and 1230–1310 nm wavelengths. The results were used to determine the rate constants for O₂(a, 0) + O₂(a, 0) → O₂(X, 0) + O₂(X, 0) + hν (λ = 634 nm) and O₂(a, 0) + O₂(a, 0) → O₂(X, 1) + O₂(X, 0) + hν (λ = 703 nm) collision-induced emission ((6.72 ± 0.8) × 10⁻²³ and (7.17 ± 0.8) × 10⁻²³ cm³/s, respectively).     

Polarized spectral properties of Er<Superscript>3+</Superscript> ions in NaGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystal

Polarized spectral properties of Er³⁺:NaGd(WO₄)₂ single crystal are reported. The crystal was grown by the Czochralski method. The Judd–Ofelt theory was applied to analyze the polarized absorption spectra and then calculate the spontaneous emission probabilities, radiative lifetimes, and branching ratios. Fluorescence decay curves of the ⁴ I _13/2, ⁴ I _11/2, and ⁴ S _3/2 multiplets for the Er³⁺ ions were measured. Stimulated emission cross-sections of the ⁴ I _13/2→⁴ I _15/2 transition obtained by the Fuchtbauer–Ladenberg formula and the reciprocity method were compared. Multi-phonon relaxation rates of the crystal were estimated. Green up-conversion fluorescence around 531 and 552 nm was observed, and the possible up-conversion mechanisms were proposed. PACS 78.20.-e; 42.70.Hj     

Synthesis and photoluminescence characteristics of doped ZnS nanoparticles

Free-standing powders of doped ZnS nanoparticles have been synthesized by using a chemical co-precipitation of Zn²⁺, Mn²⁺, Cu²⁺ and Cd²⁺ with sulfur ions in aqueous solution. X-ray diffraction analysis shows that the diameter of the particles is ∼2–3 nm. The unique luminescence properties, such as the strength (its intensity is about 12 times that of ZnS nanoparticles) and stability of the visible-light emission, were observed from ZnS nanoparticles co-doped with Cu²⁺ and Mn²⁺. The nanoparticles could be doped with copper and manganese during the synthesis without altering the X-ray diffraction pattern. However, doping shifts the luminescence to 520–540 nm in the case of co-doping with Cu²⁺ and Mn²⁺. Doping also results in a blue shift on the excitation wavelength. In Cd²⁺-doped ZnS nanometer-scale particles, the fluorescence spectra show a red shift in the emission wavelength (ranging from 450 nm to 620 nm). Also a relatively broad emission (ranging from blue to yellow) has been observed. The results strongly suggest that doped ZnS nanocrystals, especially two kinds of transition metal-activated ZnS nanoparticles, form a new class of luminescent materials. Received: 16 October 2000 / Accepted: 17 October 2000 / Published online: 23 May 2001     

Phase transition and electrical properties of (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)(Nb<Subscript>1-x</Subscript>Ta<Subscript>x</Subscript>)O<Subscript>3</Subscript> lead-free piezoelectric ceramics

(K_0.5Na_0.5)(Nb_1-xTa_x)O₃ lead-free piezoelectric ceramics have been prepared by an ordinary sintering technique. The results of X-ray diffraction reveal that Ta⁵⁺ diffuses into the K_0.5Na_0.5NbO₃ lattices to form a solid solution with an orthorhombic perovskite structure. Because of the high melting temperature of KTaO₃, the (K_0.5Na_0.5)(Nb_1-xTa_x)O₃ ceramics can be sintered at higher temperatures. The partial substitution of Ta⁵⁺ for the B-site ion Nb⁵⁺ decreases both paraelectric/cubic–ferroelectric/tetragonal and ferroelectric/tetragonal–ferroelectric/orthorhombic phase transition temperatures, T_C and T_O-T. It also induces a relaxor phase transition and weakens the ferroelectricity of the ceramics. The ceramics become ‘softened’, leading to improvements in d₃₃, k_p, k_t and ε_r and a decease in E_c, Q_m and N_p. The ceramics with x=0.075–0.15 become optimum, having d₃₃=127–151 pC/N, k_p=0.43–0.44, k_t=0.43–0.44, ε_r=541–712, tanδ=1.75–2.48% and T_C=378–329 °C. PACS 77.65.-j; 77.84.Dy; 77.84.-s     

Studies on Interaction of Norfloxacin,Cu<Superscript>2+</Superscript>, and DNA by Spectral Methods

The interactions of norfloxacin (NFA), DNA, and Cu²⁺ are studied by fluorescence and UV-spectra method. According to the experimental results, it can be concluded that NFA can form a steady binary complex with Cu²⁺. There is a linear relationship between the Fluorescence intensity of the norfloxacin–Cu²⁺–DNA system and the concentration of DNA. And when the concentration of the NFA is 1.95×10⁻⁵ mol L⁻¹, they possess a good linearity in the concentration of DNA ranged from 4.7×10⁻⁶ to 2.8×10⁻⁵ mol L⁻¹.It is a good method due to the high sensitivity and selectivity.     

Silver Nanoparticle-Enhanced Chemiluminescence Method for Determining Naproxen Based on Europium(III)-Sensitized Ce(IV)-Na<Subscript>2</Subscript>S<Subscript>2</Subscript>O<Subscript>4</Subscript> Reaction

A simple and sensitive chemiluminescence (CL) method coupled with flow-injection technique is proposed to determine naproxen (NAP). The method is based upon the enhancement of the weak CL signal arising from the reaction of Ce(IV) and Na₂S₂O₄ with Eu³⁺ to form the Eu³⁺-Ce(IV)-Na₂S₂O₄ system. The CL intensity was significantly increased by the introduction of NAP into this system in the presence of silver nanoparticles (Ag NPs). Examination of the recorded UV–vis spectra and fluorescence spectra indicated that the energy of the intermediate SO₂*, which originated from the redox reaction of Ce(IV) and Na₂S₂O₄, was transferred to Eu³⁺ via NAP and that the process was accelerated by Ag NPs due to their catalytic activity. Under the optimum conditions, the CL intensity was increased with increasing NAP concentration and the correlation was linear (r = 0.9992) over the NAP concentration range of 1–420 ng mL⁻¹. The limit of detection (LOD) was 0.11 ng mL⁻¹ with a relative standard deviation (RSD) of 1.15% for 5 replicate determinations of 200 ng mL⁻¹ NAP. The method was successfully applied to determine NAP in pharmaceutical and biological samples.     

Thermoluminescence and thermal properties of rare-earth-ion-activated YAG crystals

The paper contains results of studies of repeated thermoluminescence of yttrium-aluminum garnet (YAG) crystals (Y_3−xLn_xAl₅O₁₂, x=0, 2) activated by rare earth ions (Pr³⁺, Nd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺) previously exposed to⁶⁰Co γ-radiation at 77 K and subjected to many cooling-heating cycles. A possible mechanism of repeated thermoluminescence is considered from the viewpoint of a dynamic evolutionary approach. The thermal conductivity of YAG-TR³⁺ crystals (TR³⁺: Gd³⁺, Tb³⁺, Dy³⁺, Er³⁺, Tm³⁺, and Lu³⁺) is studied to establish its relation with repeated thermoluminescence. Presented at the National Conference on Molecular Spectroscopy, Samarkand (Uzbekistan), September 25–27, 1996. Samarkand State University, 15, University Blvd., 703004, Samarkand, Republic of Uzbekistan. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 137–140, January–February, 1998.     

Spectroscopic properties of Er<Superscript>3+</Superscript> in Sc:LiNbO<Subscript>3</Subscript> crystal

The results of Er³⁺ ion spectroscopic analysis in Sc:LiNbO₃ crystals were reported. The line strengths from the ground state to the excited state were evaluated from the measured unpolarized absorption spectrum and analyzed by using standard Judd–Ofelt theory. For Sc(3 mol. %):Er (1 mol. %):LiNbO₃ crystal, the obtained intensity parameters are: Ω₂=3.72×10^-20 cm², Ω₄=1.07×10^-20 cm², and Ω₆=0.98×10^-20 cm². The fluorescence spectra and microsecond time-resolved spectra were investigated in the visible region. The excited state absorption transition strengths at 800 nm excitation were evaluated based on Judd–Ofelt theory. The results obtained here were compared to results from other research on Er:LiNbO₃ crystals. PACS 71.20.Eh; 77.84.Dy; 42.70.Hj; 42.62.Fi; 42.65.Ky     

Broadband infrared luminescence from transparent glass–ceramics containing Ni<Superscript>2+</Superscript>-doped <Emphasis Type="BoldItalic">β</Emphasis> -Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocrystals

Transparent Ni²⁺-doped β-Ga₂O₃ glass–ceramics were synthesized. The nanocrystal phase in the glass–ceramics was identified to be β-Ga₂O₃ and its size was about 3.6 nm. It was confirmed from the absorption spectra that the ligand environment of Ni²⁺ ions changed from the trigonal bi-pyramid fivefold sites in the as-cast glass to the octahedral sites in the glass–ceramics. The broadband infrared emission centering at 1270 nm with full width at half maximum (FWHM) of more than 250 nm was observed. The fluorescence lifetime was about 1.1 μs at room temperature. The observed infrared emission could be attributed to the ³ T _2g (³ F )→³ A _2g (³ F ) transition of octahedral Ni²⁺ ions. It is suggested that the Ni²⁺-doped transparent β-Ga₂O₃ glass–ceramics with broad bandwidth and long lifetime have a potential as a broadband amplification medium. PACS 42.70.-a; 42.70.Ce; 81.40.Tv     

The Formation of Dimeric Centers of Copper,Iron and Gadolinium in Modified Pb<Subscript>5</Subscript>Ge<Subscript>3</Subscript>O<Subscript>11</Subscript>

It is discovered that the electron paramagnetic resonance (EPR) spectrum of the doubly charged copper centers occurs in single crystals of Pb₅Ge₃O₁₁ doped with gadolinium or iron after annealing in an atmosphere containing chlorine and bromine. Similar annealing of the crystals doped with copper in a chlorine and fluorine atmosphere leads to redistribution of the intensities of the EPR spectra of two types of Cu²⁺ centers. The influence of annealing on the ongoing intensity of spectra of the dimeric triclinic centers Fe³⁺–A, Gd³⁺–A (where A represent Cl^?, Br^?, O^2?, F^?) was the subject of this research. Consideration is given to the mechanisms for changing the charge state and association of copper center with defects.     

Facile patterning of luminescent GdVO4:Ln (Ln?=?Eu3+, Dy3+, Sm3+) thin films by microcontact printing process

Ordered arrays of luminescent GdVO₄:Ln (Ln = Eu³⁺, Dy³⁺, Sm³⁺) films with dot patterns have been successfully fabricated via microcontact printing method. The soft-lithography process utilizes a PDMS elastomeric mold as the stamp combined with a Pechini-type sol–gel process to produce luminescent patterns on quartz plates, in which a GdVO₄:Ln (Ln = Eu³⁺, Dy³⁺, Sm³⁺) precursor solution was employed as ink. The ordered luminescent GdVO₄:Ln patterns were revealed by optical microscopy and their microstructure, consisting of nanometer-scale particles, as demonstrated by scanning electronic microscopy observations. In addition, photoluminescence and cathodoluminescence were carried out to characterize the patterned GdVO₄:Ln (Ln = Eu³⁺, Dy³⁺, Sm³⁺) samples. Upon UV-light or electron-beam irradiation, the rare earth ions Eu³⁺, Dy³⁺, and Sm³⁺ in the crystalline GdVO₄ host show their characteristic transitions dominated by ⁵D₀–⁷F₂, ⁴F_9/2–⁶H_13/2 ,and ⁴G_5/2–⁶H_7/2, respectively. These results make the combining soft lithography with a Pechini-type sol–gel route have potential applications as rare-earth luminescent pixels for next-generation field-emission display devices.