Photoluminescence of sol–gel-derived Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> thin-film phosphors with Mg<Superscript>2+</Superscript> and Al<Superscript>3+</Superscript> co-doping

Red-light-emitting Y₂O₃:Eu³⁺ thin-film phosphors were synthesized using a sol–gel process. The effect of Mg²⁺ and Al³⁺ co-dopants on the Y₂O₃:Eu³⁺ thin-film phosphor photoluminescence (PL) property was investigated. At a certain concentration, both Mg²⁺ and Al³⁺ co-dopants were found to further enhance the PL emission intensity of Y₂O₃:Eu³⁺ thin-film phosphors. The optimum PL emission intensity was observed in Y₂O₃:12%Eu³⁺, 7%Mg²⁺ and Y₂O₃:12%Eu³⁺, 2%Al³⁺ phosphor films. From our results, the enhancement of the emission intensity by the Mg²⁺ and Al³⁺ co-dopants is explained in terms of the creation of defect states near the Y(4d+5s) conduction band, which overlap with the Eu³⁺ charge-transfer state (CTS). The overlapping leads to CTS broadening and consequently induces higher absorption and hence an increase of the emission intensity. From X-ray diffraction results, we have found that there is no additional phase formed in the co-doped phosphor films. PACS 68.55.Ln; 78.55.-m; 81.20.Fw     

Visualization of 2-μm radiation by BiF<Subscript>3</Subscript>:Ho<Superscript>3+</Superscript> and BiF<Subscript>3</Subscript>:Ho<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> ceramics

A series of ceramic samples of the compositions BiF₃:1%Ho³⁺, BiF₃:4%Ho³⁺, BiF₃:1%Ho³⁺ + 1%Yb³⁺, and BiF₃:1%Ho³⁺ + 3%Yb³⁺ is synthesized and the conversion of Tm:YLF laser radiation (λ = 1908 nm) is studied. The luminescence spectra exhibit bands in the regions of 490, 545, and 650 nm. The kinetic measurements of the afterglow of the green and red bands show that the population of the ⁵S₂ and ⁵F₄ states in the BiF₃:1%Ho³⁺ samples occurs due to successive absorption of excitation photons, while the ⁵F₅ level of Ho³⁺ is populated due to the ion–ion interaction. Codoping with Yb³⁺ leads to a decrease in the visualization threshold power density to 2 W/cm².     

O<Subscript>2</Subscript> photodesorption from AuO<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> and Au<Subscript>2</Subscript>O<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack>

Using time-resolved photoelectron spectroscopy, the decay channels of AuO₂⁻ and Au₂O₂⁻ following photoexcitation with 3.1-eV photons have been studied. For AuO₂⁻, a state with a rather long lifetime of 30 ps has been identified. Its decay path could not be determined but photodesorption can be excluded. For Au₂O₂⁻, the spectra indicate O₂ desorption after 3.1-eV photoexcitation on a time scale of 1 ps. While comparing these results on Au _n O₂⁻ with analogous data on Ag _n O₂⁻ clusters, a discernible pattern emerges: for dissociatively bound O₂(AuO₂⁻, Ag₃O₂⁻), there are long-living excited states which do not decay by oxygen desorption, while for molecular chemisorption (Au₂O₂⁻, Ag₂O₂⁻, Ag₄O₂⁻, Ag₈O₂⁻), the 3.1-eV photoexcitation triggers fast O₂ desorption with a high quantum yield.     

Hydrothermal synthesis,characterization, and luminescence of Ca<Subscript>2</Subscript>B<Subscript>2</Subscript>O<Subscript>5</Subscript>:RE (RE = Eu<Superscript>3+</Superscript>, Tb<Superscript>3+</Superscript>, Dy<Superscript>3+</Superscript>) nanofibers

Ca₂B₂O₅:RE (RE = Eu³⁺, Tb³⁺, Dy³⁺) nanofibers were synthesized by the hydrothermal reaction method. The structural refinement was conducted on the base of the X-ray powder diffraction (XRD) measurements. The surface properties of the Ca₂B₂O₅:RE (RE = Eu³⁺, Tb³⁺, Dy³⁺) nanofibers were investigated by the measurements such as the scanning electron microscope (SEM), transmission electron microscope (TEM), and the energy dispersive spectrum (EDS). The nanofiber has a diameter of about 100 nm and a length of several micrometers. The luminescence properties such as photoluminescence excitation (PLE) and emission spectra (PL), decay lifetime, color coordinates, and the absolute internal quantum efficiency (QE) were reported. Ca₂B₂O₅:Eu³⁺ nanofibers show the red luminescence with CIE coordinates of (x = 0.41, y = 0.51) and the luminescence lifetime of 0.63 ms. The luminescence of Ca₂B₂O₅:Tb³⁺ nanofibers is green color (x = 0.29, y = 0.53) with the lifetime of 2.13 ms. However, Dy³⁺-doped Ca₂B₂O₅ nanofibers present a single-phase white-color phosphor with the fluorescence decay of 3.05 ms. Upon near-UV excitation, the absolute quantum efficiency is measured to be 65, 35, and 37 % for Eu³⁺-, Tb³⁺-, Dy³⁺-doped Ca₂B₂O₅ nanofibers, respectively. It is suggested that Ca₂B₂O₅:RE (RE = Eu³⁺, Tb³⁺, Dy³⁺) nanofibers could be an efficient phosphor for lighting and display.     

Calix[4]arene Based Dual Fluorescent Sensor for Al<Superscript>3+</Superscript> and S<Subscript>2</Subscript>O<Subscript>7</Subscript><Superscript>2−</Superscript>

Specific functionalized calix[4]arene based fluorescent chemosensor was synthesized for cations and anions binding efficiency examination. Receptor C4MA displayed strong affinity for Al³⁺and S₂O₇ ^2? with enhanced fluorescence intensity. The selective response of C4MA was investigated in the presence of different co-existing competing ions. The limit of detection (LOD) of Al³⁺and S₂O₇ ^2? was calculated as 2.8?×?10^?6 M and 2.6?×?10^?7 M respectively. Sensor C4MA forms (1:1) stoichiometric complex with both Al³⁺ and S₂O₇ ^2? and their binding constants were calculated as 12.1?×?10⁴ and 8.3?×?10³ respectively. Complexes were also characterized through FT-IR spectroscopy.

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Synthesis and electrochemical performance of amorphous nickel hydroxide codoped with Fe<Superscript>3+</Superscript> and CO<Stack><Subscript>3</Subscript><Superscript>2−</Superscript></Stack>

Amorphous nickel hydroxide codoped with Fe³⁺ and CO₃²⁻ was synthesized by micro-emulsion precipitation method combined with rapid freezing technique. The microstructure and composition of the sample were characterized by X-ray diffraction and IR analysis. The electrochemical performance of the sample was analyzed by cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge tests. The results showed that the Fe³⁺ and CO₃²⁻ codoping enhances the amorphous feature of the prepared nickel hydroxide. Moreover, the Fe³⁺ and CO₃²⁻ codoping could increase the specific capacity and improve the electrochemical reversibility of the amorphous nickel hydroxide electrode.     

Visible up-conversion and NIR luminescence studies of LiAl<Subscript>5</Subscript>O<Subscript>8</Subscript>:Er phosphor co-doped with Yb<Superscript>3+</Superscript> and Zn<Superscript>2+</Superscript>

The frequency up-conversion, an efficient laser emission and amplification in Er³⁺:LiAl₅O₈ phosphors co-doped with Yb³⁺ and Zn²⁺ phosphor powders in the 520–560, 640–680 nm regions and at ∼1.5 μm, respectively, have been reported. The emission corresponds to the ²H_11/2, ⁴S_3/2→⁴I_15/2, ⁴F_9/2→⁴I_15/2 and ⁴I_13/2→⁴I_15/2 transitions upon direct excitation into the intermediated ⁴I_11/2 level using ∼980 nm radiation from a CW laser. Possible mechanisms involved for the up-conversion processes based on the energy level matching scheme, the pump-power dependence and the dynamical behaviour have been discussed. The effect of the addition of Yb³⁺ and Zn²⁺ for the amplification in the 1.5 μm eye-safe telecommunication window has been elaborated and characterized in detail.     

Optimizing after-glow luminescent parameters of Sr<Subscript>4</Subscript>Al<Subscript>14</Subscript>O<Subscript>25</Subscript>:Eu<Superscript>2+</Superscript>, Dy<Superscript>3+</Superscript>, by sol–gel method and combustion process

Strontium aluminates are viewed as a promising persistent luminescent materials. There are many researches on strontium aluminates, including SrAl₂O₄, Sr₄Al₁₄O₂₅. Between these two phases, Sr₄Al₁₄O₂₅ shows much better properties than SrAl₂O₄. The traditional way to synthesize Sr₄Al₁₄O₂₅ is the solid state reaction. However, it exists few problems, especially non-homogeneous product. As a result, there are two methods chosen to make homogeneous precursor. One is sol–gel method, the other is combustion with Urea as a fuel. Boric acid is added as a flux in both method. In this study, combustion process is found to be a better way for synthesizing Sr₄Al₁₄O₂₅. We change the temperature, synthetic method. The samples are finely grinded and used for XRD analysis, photoluminescence measurement, and after-glow decay curve to figure out the optimizing luminescent parameters.     

Frequency upconversion properties of Ag: TeO<Subscript>2</Subscript>–ZnO nanocomposites codoped with Yb<Superscript>3+</Superscript> and Tm<Superscript>3+</Superscript> ions

Yb³⁺–Tm³⁺ codoped tellurite glasses containing silver nanoparticles (NPs) were synthesized and characterized using transmission electron microscopy and optical techniques. The samples’ composition and the nucleation of NPs were investigated using electron diffraction and energy dispersive spectroscopy. For the optical experiments, the samples were excited using a diode laser operating at 980 nm, in resonance with the Yb³⁺ transition ²F_7/2→²F_5/2. Photoluminescence (PL) bands corresponding to Tm³⁺ transitions were observed at 480, 650, and 800 nm due to the Yb³⁺→ Tm³⁺ energy transfer. PL enhancement was achieved by heat-treatment of the samples at 325°C during different time intervals. The growth of the PL bands correlates with the increase of the silver NPs concentration. The relevant mechanisms contributing for the PL characteristics are discussed.     

Spectroscopic analysis of Pr<Superscript>3+</Superscript> crystal-field transitions in YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>

Yttrium aluminium borate single crystals, doped with 1 and 4 mol% of Pr³⁺, were analyzed in the wave number range 500–25000 cm⁻¹ and temperature range 9–300 K by means of high-resolution Fourier transform spectroscopy. In spite of the complex spectra, exhibiting broad and split lines, the energy level scheme was obtained for several excited manifolds. The careful analysis of the spectra as a function of the temperature allowed us to identify most of the sublevels of the ground manifold. The thermally induced line shift, well described by a single-phonon coupling model, could be exploited to provide information about the energy of the phonons involved. The orientation of the dielectric ellipsoid and of the dipole moments associated to a few transitions was also determined from linear dichroism measurements. The experimental data were fitted in the framework of the crystal-field theory, but the agreement was not satisfactory, as already reported for Pr³⁺ ion in other matrices. Additional discrepancies came from the dichroic spectra analysis and the line splitting, possibly associated to hyperfine interaction. Some causes which might be responsible for the difficulties encountered in the Pr³⁺ ion theoretical modelling are discussed.     

Hyperfine Interactions in Pb<Superscript>3+</Superscript>F<Stack><Subscript>8</Subscript><Superscript>−</Superscript></Stack>F<Stack><Subscript>a</Subscript><Superscript>−</Superscript></Stack> clusters in fluorite crystals

The parameters of hyperfine interactions in Pb³⁺F ₈ ^? F _a ^? tetragonal clusters of MeF₂ crystals (Me=Ca, Sr, Ba) are interpreted. The contributions of the spin polarization to the parameters of the proper hyperfine interaction and additional (ligand) hyperfine interactions are calculated in the approximation of weak binding between a charge-compensating ion F _a ^? and a cubic fragment in the tetragonal cluster. It is demonstrated that correct inclusion of the contributions from the spin polarization to the ligand isotropic hyperfine interaction for the F _a ^? ion leads to anomalously large parameters of this interaction for MeF₂ crystals. These results are in agreement with experimental data.     

Concentration quenching of Eu<Superscript>2+</Superscript> in a novel blue–green emitting phosphor: Ba<Subscript>2</Subscript>ZnSi<Subscript>2</Subscript>O<Subscript>7</Subscript>:Eu<Superscript>2+</Superscript>

A novel blue–green emitting phosphor Ba₂ZnSi₂O₇: Eu²⁺ was prepared by a combustion synthesis (CS) method. An efficient green emission under conditions ranging from ultraviolet to visible light was observed. The emission spectrum shows a single intensive band centered at 503 nm, which corresponds to the 4f ⁶5d ¹→4f ⁷ transition of Eu²⁺. The excitation spectrum is a broad band extending from 260 to 465 nm, which matches the emission of ultraviolet light-emitting diodes (UV-LEDs). The critical quenching concentration of Eu²⁺ in Ba₂ZnSi₂O₇:Eu²⁺ phosphor is about 0.05 mol. The corresponding concentration quenching mechanism is verified to be a dipole–dipole interaction. The value of the critical transfer distance is calculated as 19 Å, which is in good agreement with the value (20 Å) derived from the experimental data.     

Potential energy of <Superscript>∞</Superscript>H<Stack><Subscript>2</Subscript><Superscript>-</Superscript></Stack>(<Superscript>2</Superscript>∑<Stack><Subscript>u</Subscript><Superscript>+</Superscript></Stack> in the bound-state region

An accurate calculation of the lowest negative electronic state of H ₂ ^- (fixed nuclei) is reported using the CCSD(T) method and doubly augmented cc-pv5z basis set. Comparison has been made with the reference data by Senekowitsch et al. [Chem. Phys. Lett. 111 (1984) 211]. Owing to larger size of the basisset and inclusion of triple excitations, no vertical shift in this work is necessary to reproduce the asymptotics of H + H ^-. In addition, the effect of basis-set truncation is estimated, based on the complete-basis-set extrapolation method. The contribution of correlated electron-proton motion to the electron-energy curve for H₂ ^– dynamics is pointed out.Dedicated to Prof. Jií Horáek on the occasion of his 60th birthday.     

110 W ceramic Nd<Superscript>3+</Superscript> : Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> laser

A high-power, continuous-wave 0.6% Nd³⁺-doped ceramic Y₃Al₅O₁₂ (Nd:YAG) laser has been developed. 110 W laser output at 1064 nm was obtained, with a slope efficiency of about 41%. The M² factor was found to be around 6. The laser performance of the ceramic laser material was found to compare favorably with that obtained with single crystal Nd:YAG. PACS 42.55.-f; 42.55.Xi; 42.70.Hj     

Electron paramagnetic resonance of Er<Superscript>3+</Superscript> ions in a polycrystalline α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The EPR spectra of rare-earth Er³⁺ ions in a polycrystalline corundum α-Al₂O₃ synthesized by the sol-gel technology were revealed. It is shown that the EPR spectra belong to the Er³⁺ ions in the ground state corresponding to the lower Stark sublevel of the ⁴ I _15/2 term and can be described by the spin Hamiltonian of axial symmetry with an effective spin S = 1/2 and the g tensor with components g _‖ = 12.176 and g _⊥ = 4.14. The average value of the g tensor (〈g〉 = 6.82) corresponds to the Γ₇ state in a cubic field. Erbium is assumed to substitute for aluminum in the Al₂O₃ corundum crystal. The local symmetry C ₃ of the Al³⁺ ion remains despite the pronounced expansion of the lattice around the Er³⁺ ion.     

Luminescence properties of Nd<Superscript>3+</Superscript>-doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in organic media

Nd³⁺-doped yttrium oxide nanoparticles (Y₂O₃:Nd) with cubic phase were obtained successfully by a glycine-nitrate solution combustion method. The results of Fourier transform infrared spectra (FTIR) showed that the –OH groups residing on the nanoparticles surfaces were reduced effectively by modifying with capping agent. The modified Y₂O₃:Nd nanoparticles displayed good monodispersity and excellent luminescence in N,N-dimethylformamide (DMF) solvent. Some optical parameters were calculated by Judd–Ofelt analysis based on absorption and fluorescence spectra. A relative large stimulated emission cross section, 1.7×10⁻²⁰ cm², of the ⁴F_3/2→⁴I_11/2 transition was calculated. Theses results show that the modified Y₂O₃:Nd nanoparticles display good luminescence behavior in organic media.     

Enhancing up conversion luminescence effect of β-NaYF<Subscript>4</Subscript>: Yb<Superscript>3+</Superscript> and Tm<Superscript>3+</Superscript> by Li<Superscript>+</Superscript> ion doped approach

Up-conversion (UC) is a photoluminescence process which converts few low energy photons to a higher energy photon. This process has more potential usages in many different fields like bioimaging, solar spectrum tuning, and security encoding. Nowadays, researches about UC mostly focusing on biomedical signory and synthesis of nanoparticles. The synthesis of NaYF₄ nanoparticles executed under series of pH value condition results in different morphology and photoluminescence effect. Samples in low pH value created better consequent and quality than the specimen which had higher pH value. In addition, we observed NaYF₄ samples of doping Li⁺, realizing that the action of distorting in the local symmetry around rare-earth ions is caused by Li⁺ doping. The NaYF₄ microparticles which doped higher concentration of Li⁺ has strong fluorescence properties and intensities compared with their corresponding group of Li⁺-free, the blue emission 479 nm luminescence intensities and 454 nm luminescence intensities in NaYF₄:Yb³⁺, Tm³⁺ microparticles doped 20 mol% Li⁺ are enhanced 3 and 8 times, separately. And violet emission luminescence intensities around 345 and 360 nm are about 10 and 7 times, respectively. The result indicated that the improved UC luminescence of NaYF₄:Yb³⁺. Tm³⁺ microparticles with Li⁺ doping have potentially applications.     

Temperature dependence of the quenching of N<Subscript>2</Subscript> (C <Superscript>3</Superscript>Π<Subscript>u</Subscript>) by N<Subscript>2</Subscript> (X) and O<Subscript>2</Subscript> (X)

The temperature dependences of the quenching rate constants of the states N₂ (${\rm C} \ {^{3}{ \rm \Pi }_{u}}${\rm C} \ {^{3}{ \rm \Pi }_{u}} v^′=0,1) by N₂ (X) and of the state N₂ (${\rm C} \ {^{3}{ \rm \Pi }_{u}} \ v^{\prime}=0${\rm C} \ {^{3}{ \rm \Pi }_{u}} \ v^{\prime}=0) by O₂ (X) are studied. Time-resolved light emission from the gas was analyzed in the temperature range from 300 K to 210 K keeping the gas at constant density. In case of quenching by N₂ (X), the quenching rate constant for the vibrational level v^′= 0 increases by (13 ±3)% with gas cooling whereas the quenching rate constant for v^′= 1 decreases by (5.0 ±2.5)% in this temperature range. For quenching by O₂ (X), the quenching rate constant decreases by (3 ±2)% with gas cooling. The temperature variation of the N₂ (C ³Π_u v^′=0) emission intensity for pure nitrogen and dry air are calculated using the obtained quenching rate constants and is compared with the experimental data available in the literature.     

Analysis of the vector form factors f<Superscript>+</Superscript><Subscript>Kπ</Subscript>(Q<Superscript>2</Superscript>) and f<Superscript>-</Superscript><Subscript>Kπ</Subscript>(Q<Superscript>2</Superscript>) with light-cone QCD sum rules

In this article, we calculate the vector form factors f⁺ _Kπ(Q²) and f^- _Kπ(Q²) within the framework of the light-cone QCD sum rule approach. The numerical values of f⁺ _Kπ(Q²) are compatible with existing theoretical calculations, and the central value of f⁺ _Kπ(0) (f⁺ _Kπ(0)=0.97) is in excellent agreement with the values from chiral perturbation theory and lattice QCD. The values of |f^- _Kπ(0)| are very large compared to the theoretical calculations and experimental data, and they cannot give any reliable prediction. At large momentum transfer with Q² > 5 GeV², the form factors f⁺ _Kπ(Q²) and |f^- _Kπ(Q²)| can either show the asymptotic behavior of or decrease more quickly than ; more experimental data are needed to select the ideal sum rules. PACS 12.38.Lg; 12.38.Bx; 12.15.Hh     

EIT Ground State Cooling Scheme of <Superscript>171</Superscript>Yb<Superscript>+</Superscript> Based on the <Superscript>2</Superscript>S<Subscript>1/2</Subscript>→<Superscript>2</Superscript>P<Subscript>1/2</Subscript> Cooling Transition

We propose a method for EIT ground state cooling of ¹⁷¹Yb+ ion, which involves three light fields with detuning on a MHz scale. The steady-state mean vibrational quantum number is calculated to be less than 0.005. Efficient cooling is achievable in a motional-mode frequency range of 2π · (1.5 ± 0.5 MHz).