Specific features of the luminescence of silicate glasses with silver introduced by ion exchange

The luminescence spectra of silicate glasses with silver introduced by ion exchange have been investigated. It is shown that silver introduced into glass by ion exchange exists not only in the form of ions, but also as neutral atoms and charged and neutral molecular clusters, which provide intense luminescence in the visible spectral range. Cerium ions in glass facilitate the formation of neutral molecular silver clusters, due to which the luminescence intensity increases. It is shown that Ag _n -Ce ^x+ complexes can be formed in glass containing cerium ions and neutral molecular silver clusters.     

Influence of UV irradiation and heat treatment on the luminescence of molecular silver clusters in photo-thermo-refractive glasses

The luminescence spectra of photo-thermo-refractive (PTR) glasses containing cerium, silver, and antimony ions before and after UV irradiation and after heat treatment have been thoroughly investigated for the first time. It is shown that silver is present in the initial PTR glass in the form of ions and positively charged molecular clusters. After UV irradiation into the absorption band of cerium ions, silver partially passes to the neutral state in the form of atoms and neutral molecular clusters Ag₂, Ag₃, and Ag₄, which exhibit bright luminescence in the visible spectral range. Subsequent heat treatment at a temperature below the glassformation temperature leads to an increase in the luminescence intensity due to the increase in the concentration of neutral molecular clusters. Heat treatment at a temperature above the glass-formation temperature leads to the formation of silver nanocrystals and luminescence quenching. It is proposed to use PTR glasses with molecular silver clusters as phosphors for converting UV radiation into the visible range for solar power engineering and white LEDs.     

Broadband copper luminescence in potassium-aluminum borate glasses

Broadband luminescence in the visible spectral range has been investigated for copper-containing potassium-aluminum borate glasses. It is shown that the luminescence in initial glasses (before their heat treatment) is due to the presence of molecular clusters Cu _n (n < 10) in them. Chemical reactions during heat treatment lead to the formation of Cu _n Cl _x and Cu _n O _x clusters with luminescence bands lying in the spectral range of 450–600 nm.     

Spectral luminescence properties of bee glue (propolis)

The photoluminescence intensity of an alcoholic solution of propolis at room temperature is studied as a function of the propolis concentration. It is found that, unlike in most organic substances and complex compounds (including natural bee honey), where luminescence is maximal at a certain solute-to-solvent ratio, the luminescence intensity increases with the concentration of propolis and is maximal in elastic solid films. Variation of the film’s temperature in the range from 520 to 570 K causes neither a shift of the fundamental absorption edge nor a qualitative change in the photoluminescence spectrum (E _max = 2.9 eV at T = 300 K) but leads to a decrease in the luminescence intensity. This effect may be due to the disturbance of molecular order in the films under study. It is inferred that propolis deserves attention as a promising optoelectronic material.     

A Mechanism of the influence of Gd(III) and other Ln(III) ions on sensitized luminescence of Eu(III) and Tb(III) ions in aqueous and ethanol solutions: The role of hydroxyl bridges

We studied sensitization of Eu(III) and Tb(III) ions by molecules of 1,10-phenanthroline and 2,2-bipyridil in D₂O and d ₆-ethanol and the influence of Nd(III), Pr(III), Sm(III), Gd(III), and Ho(III) ions on the luminescence intensity I _lum and lifetime τ_lum of Eu(III) and Tb(III) in solutions. The stability constants of complexes of Eu(III) and Gd(III) with 2,2′-bipyridil are measured by spectrophotometric and luminescence methods. It is shown that luminescence of Eu(III) is quenched by Gd(III) ions at the ion concentration equal to 10^?2–10^?1 M, which is caused by competing between these ions for a sensitizer. At the concentration of Ln(III) ions equal to 10^?6?10^?3 M, the sensitized luminescence of Eu(III) and Tb(III) was quenched and τ_lum decreased in the presence of Nd(III) ions, whereas in the presence of Gd(III) the luminescence intensity increased. It is proved that a bridge that connects the two ions upon energy transfer is formed by hydroxyl groups. The intensity of luminescence of Eu(III) and Tb(III) in aqueous solutions and its lifetime decreased in the presence of hydroxyl groups, while upon addition of Gd(III) to these solutions these quantities were restored. We also found that the addition of Gd(III) to deoxygenated ethanol solutions of 2,2′-bipyridil and Eu(III) slows down photochemical and thermal reactions between bipyridil and Eu(III), resulting in the increase in the luminescence intensity of Eu(III).     

Lyoluminescence mechanism of additively and gamma coloured alkali halides in fluorescent and chemiluminescent solutions

Lyoluminescence of gamma irradiated and additively coloured NaCl, NaBr, KCl and KBr crystals when dissolved in fluorescent and chemiluminescent aqueous solutions is investigated. Spectral analysis of the emitted light has shown that lyoluminescence spectra are similar to the fluorescence spectra of these solutions. Luminescence takes place when a fluorescent acceptor is directly excited by a liberated F-centre (hydrated electron e^-_aq) or indirectly by an energy transfer from a released excited halide ion ∥X^-∥¹ (solvated hole after recombination with hydrated electron). Oxygen, in general, has a marked quenching effect on luminescence. In chemiluminescent systems, its presence is essential to provoke luminescence in a sequence of events leading to a fluorescent end product.     

Visible luminescence of the fluoride glass ZBLAN with thulium and ytterbium under IR diode laser pumping

Visible luminescence of thulium in the fluorozirconate glass ZBLAN sensitized with ytterbium is studied experimentally under IR diode laser pumping. Variation of the blue luminescence intensity at a wavelength of 472 nm (the ¹ G ₄ → ³ H ₆ transition) with the pump power and ytterbium concentration is analyzed. The effect of the host-matrix composition on the luminescence characteristics is studied. A strong enhancement of the upconversion efficiency at low temperatures is found.     

碱金属卤化物气相团簇的质谱与密度泛函理论研究

利用自制的电喷雾电离源与大气压力接口飞行时间质谱相结合,成功观察到了一系列的Cl^-(NaCl)_n和Br^-(NaBr)_m阴离子团簇．研究发现,Cl^-(NaCl)_n体系中n=4和7时质谱的相对丰度较高,被认为是幻数团簇,而其同系物Br^-(NaBr)_m,则发现了不同的质谱峰形,反映了这两种盐溶液在液相成核当中具有细微的差异．基于密度泛函理论的全局最小值搜索程序进一步验证了实验上的发现,显示出n=4和7时是最稳定的结构．另外对这类体系的能量计算发现它们的垂直解离能非常的高,即所谓的超级卤素     

Luminescence properties of LaBr<Subscript>3</Subscript>:Ce microcrystals dispersed in NaBr matrix

The formation of LaBr₃-Ce microcrystals 1–10 μm in size dispersed in a NaBr matrix has been revealed in a NaBr-LaBr₃(1%)-CeBr₃(0.05%) crystal by electron microprobe analysis and luminescence spectroscopy. The spectral-luminescence and luminescence-kinetic characteristics of the NaBr-LaBr₃(1%)-CeBr₃(0.05%) crystal under optical and X-ray excitations have been investigated. The spectral-luminescence properties of LaBr₃:Ce microcrystals dispersed in an NaBr matrix are identical to those in the bulk analogs. The mechanisms of energy transfer to Ce³⁺ ions during crystal excitation in the ranges of transparency and fundamental absorption of NaBr and LaBr₃ matrices are discussed.     

Photostimulated luminescence flash: from scientific photography to photonics of nanostructured materials

We have analyzed the possibilities of using the phenomenon of photostimulated luminescence flash for optical diagnosing of energy levels of structural and impurity defects of semiconductor crystals and nanostructures. New data on the spectra of deep localized states associated with adsorbed few-atom clusters Zn _n on the surface of ZnS; clusters Cd _n , Cu _n , and Ag _n on the surface of CdS; and clusters Ag _n on the surface of AgBr(I) have been presented, as well as results of investigation of photostimulated assembling processes of few-atom clusters on the surface of crystals using this phenomenon. We are the first to show the potential of the luminescence flash technique for studying the mutual arrangement of the levels of dye molecules and the bands of the crystal on the surface of which they are adsorbed, as well as of the spectra of localized states in colloidal CdS semiconductor quantum dots.     

Nonlinear light absorption and luminescence in silicate glasses

The study of luminescence of high-purity multicomponent silicate glasses excited by radiation of a N₂ laser (λ=337 nm, P≈12kW) showed darkening of a sample and a monotone decrease in luminescence intensity and the transmitted radiation intensity from pulse to pulse. Additional illumination with radiation of an Ar⁺ laser (λ=514.5 nm) caused an increase in luminescence intensity. An increase in absorption and a decrease in luminescence intensity were found to be caused by two-photon absorption and electron-hole pair production.     

An investigation on visible luminescence of Ho activated LBTAF glasses

Different concentrations of Ho³⁺-doped lead borate titanate aluminum fluoride (LBTAFHo) glasses with chemical composition of PbO-H₃BO₃-TiO₂-AlF₃-Ho₂O₃ were prepared by the melt quenching method. The spectral properties were investigated using the absorption, emission and decay measurements. The experimental oscillator strengths were calculated from the area under the absorption bands. Applying Judd-Ofelt theory, the intensity parameters (Ω_{λ=2, 4, 6}) were calculated, by the least square fit approach from which the radiative transition rates, luminescence branching ratios and radiative decay times were determined. The photoluminescence spectra revealed the quenching of luminescence intensity beyond 1.0 mol% of Ho³⁺ ion concentration. To investigate the luminescence potentiality of ⁵F₄→⁵I₈ emission level, the effective bandwidth and the stimulated emission cross-section were determined. The quenching in experimental decay time is attributed to the resonance energy transfer among the excited Ho³⁺ ions.     

The influence of Mn content on luminescence properties in Mn-doped ZnO films deposited by ultrasonic spray assisted chemical vapor deposition

Mn-doped ZnO (Zn_1−xMn_xO, 0 ≤ x ≤ 0.1) films are prepared by an ultrasonic spray assisted chemical vapor deposition method. X-ray diffraction and Raman scattering show that all the Zn_1−xMn_xO films are good wurtzite structures without any impurity phases. Cathodoluminescence spectra show that ultraviolet emission and green luminescence can be observed. The intensity of ultraviolet emission decreases with the increment of x, while the intensity of green luminescence increases with the increment of x when x ≤ 0.02. However, when x (x > 0.02) is further increased, the intensity of green luminescence decreases gradually, and the green luminescence disappears when x is above 0.075. We consider that the change of the luminescence is related to the competition between the radiative recombination and the non-radiative recombination.     

Lattice model calculation of hugoniot curves and the grüneisen parameter at high pressure for the alkali halides

A seven parameter shell model of the interatomic forces in the NaCl lattice is used to make a detailed lattice dynamics calculation at arbitrary volume, for fourteen alkali halides. The calculated normal mode spectrum gives an explicit vibrational contribution to the pressure and the elastic constants in the quasiharmonic approximation. The seven parameters are chosen to fit low pressure ultrasonic data and the low and high frequency dielectric constants. Prediction of the Grüneisen parameter γ, (?lnγ/?lnV), and δ_s = (?1/βB_s)(dB_s/dT) are in reasonable agreement with experiment. The calculated γ decreases monotonically with volume. Calculated Hugoniots are in good agreement with experiment for NaCl, NaBr and NaI, and in fair agreement for LiBr, LiI and NaF.     

The hopping motion of the self-trapped exciton in NaCl

The decay kinetics and the yield of the π luminescence from the lowest triplet state of the self-trapped exciton have been studied in NaCl containing Li⁺ ions. It is found that the π luminescence band which is observed at 6K is replaced by a luminescence band peaked at 3.34 eV above 77K. The 3.34 eV luminescence band is ascribed to the recombination of the relaxed exciton trapped by a Li⁺ ion, (V_ke)_Li. The decay of the π luminescence induced by an electron pulse and the time change of the luminescence from (V_ke)_Li are explained in terms of the characteristic equation of the diffusion-limited reaction of the lowest triplet self-trapped excitons with the Li⁺ ions. From the analysis of the dependence of the decay rate of the π luminescence on temperature and on the Li⁺ concentration, we found the diffusion constant D of the lowest triplet self-trapped exciton in NaCl to be given by with $\text{D}{}_0\text{= 2.13 × 10}{}^{\mathrm{?3}}\text{cm}{}^2\text{s}$ and E₀ = 0.13 eV. The present result can be regarded as the first clear experimental evidence for the hopping diffusion of the self-trapped exciton in alkali halides. The obtained values of E_a and D₀ are discussed using the small polaron theory. The effect of the anharmonicity on the hopping of the self-trapped excitons is suggested to be significant.     

Self-diffusion coefficients and orientational correlation times in aqueous NaCl solutions: Complementarity with structural investigations

The dynamical properties of pure water and aqueous NaCl solutions over a wide range of salt concentrations (0-6 m) at ambient conditions are characterized by molecular dynamics (MD) simulations. MD simulations are performed with a flexible SPC water model as a solvent, while the ions are treated as charged Lennard-Jones particles. In this paper, attention has been focused on the self-diffusion coefficients (D_i) of ions and water molecules and on orientational correlation time of water molecules. It is found that the self-diffusion coefficients decrease with ion concentration. Moreover, the self diffusion coefficients of sodium and chloride at higher salt concentrations are very comparable which may be due to the formation of clusters of these ions. The deduced rotational dynamics speeds up as the salt concentration increases. Some complementarities between dynamical properties and structural ones, recently obtained, are carried out.     

ESR studies of europium ions in alkali chlorides and bromides

ESR studies of europium ions in alkali chlorides and bromides were performed at room and liquid nitrogen temperatures. There were first reported spin Hamiltonian parameters for NaBr: Eu²⁺ and RbBr: Eu²⁺ crystals and also for coagulated europium ions in NaCl, KCl, KBr and RbBr crystals. The dependence of b₂⁰ and b₂² on the lattice constant, a, of host crystals was discussed; a single relation b₂⁰αa^?2.6 was obtained, while relations for b₂² were treated seperately for Na, K and Rb halide series, respectively. From the relative values of b₂² and b₂⁰, displacements of the nearest neighbor anions surrounding the Eu²⁺-vacancy pair were estimated to be 0.083a for NaCl and NaBr, 0.081a for KC1, 0.080a for KBr, 0.074a for RbCl and 0.078a for RbBr.     

Synthesis, characterization, and oxygen sensing properties of Ru(II) complex covalently grafted to mesoporous MCM-41

Novel oxygen sensing materials consisting of [Ru(Bphen)₂bpy]²⁺ (Bphen=4,7-diphenyl-1,10-phenanthroline, bpy=2,2′-bipyridyl) portion covalently grafted to the backbones of the ordered functionalized mesoporous MCM-41 are synthesized by co-condensation of tetraethoxysilane (TEOS) and the functionalized Ru(II) complex [Ru(Bphen)₂Bpy-Si]²⁺ using surfactant cetyltrimethylammoniumbromide (CTAB) as template. The Bpy-Si was used as not only one of the precursors of the sol-gel process but also the second ligand of Ru(Bphen)₂Cl₂·2H₂O complex to prepare the functionalized mesoporous materials for oxygen sensors. Dye leaching shortcoming is overcome due to the Si-C bonds. The derivative mesoporous oxygen sensing materials are characterized by Fourier transform infrared (FT-IR), small angle X-ray diffraction (SAXRD), luminescence intensity quenching Stern-Volmer plots, and excited-state decay analysis. The mesoporous materials show higher sensitivity to the O₂ concentration in N₂ (I₀/I₁₀₀=23.2) and shorter response time (1.2 s) in comparison with those based on sol-gel method. When the concentration of oxygen is 10%, the luminescence intensity of the oxygen sensor can be quenched by 89.9%, suggesting that it is highly sensing at low concentration of oxygen.     

Optical properties of nanoplasmon excitations in clusters of endometallofullerenes

The optical properties of solutions of endometallofullerenes with lanthanides (Gd@C₈₂, Ce@C₈₂, La@C₈₂, Y@C₈₂) in dimethylformamide are studied. It is found that these solutions luminesce in the visible region. This luminescence is accompanied by enhanced Raman scattering. It is suggested that these processes are related to nanoplasmon excitations in clusters of endometallofullerenes. It is shown that the luminescence spectrum is described by a superposition of three to four Gaussian spectral profiles, whose energy positions and intensities nonmonotonically depend on the energy of excitation quanta. A detailed quantitative dependence of the intensity and shape of the Raman scattering signal on the concentration of endometallofullerenes in the solutions is determined. Comparative measurements are performed for the emission spectra of solutions of simple fullerenes and chromatographically pure endometallofullerenes. Complex investigations show that the visible luminescence and Raman scattering enhancement are only observed in the case of the formation of nanosized anionic complexes of endometallofullerenes in the solution.     

Luminescence properties of solid solutions of borates doped with rare-earth ions

The structural and luminescence properties of Lu _x Y_{1 ? x} BO₃ solid solutions doped with Ce³⁺ or Eu⁺³ have been investigated. It has been found that the solid solutions crystallize in the vaterite phase with a lutetium concentration x < 0.5. For a higher lutetium concentration x, the solid solutions contain an additional calcite phase with a content less than 5 wt %. The luminescence spectra are characterized by intensive impurity emission under excitation with the synchrotron radiation in the X-ray and ultraviolet spectral ranges. It has been shown that, as the lutetium concentration x in the Lu _x Y_{1 ? x} BO₃: Ce³⁺ solid solutions increases, the emission intensity smoothly decreases, which is associated with a gradual shift of the Ce³⁺ 5d(1) level toward the bottom of the conduction band, as well as with a decrease in the band gap. It has been established that, in the Lu _x Y_{1 ? x} BO₃: Eu³⁺ solid solutions with intermediate concentrations x, the efficiency of energy transfer to luminescence centers increases. This effect is explained by the limited spatial separation of electrons and holes in the solid solutions. It has been demonstrated that the calcite phase adversely affects the luminescence properties of the solid solutions.