Synthesis and study of IR luminescence of Ln<Subscript>2</Subscript>O<Subscript>2</Subscript>S:Yb (Ln = Y,La, Gd) under laser excitation

The ranges of the existence of solid solutions in binary systems Ln₂O₂S-Yb₂O₂S(Ln = Y, La, Gd) were found and main features of variations of Stokes IR luminescence intensity of Ln₂O₂S·Yb in the range of 0.96–1.1 μm were determined depending on the composition during IR excitation. Based on the established features, a new Y₂O₂S:Yb monospectral IR phosphor was developed, which, upon excitation by a 0.940-μm laser, is characterized by an increased Stokes IR luminescence intensity in the range of 0.96–1.1 μm in comparison with that of known commercial phosphor.     

A simple and sensitive fluorescence quenching method for the determination of H(2)O(2) using Rhodamine B and FE(3)O(4) nanocatalyst

In pH 1.99 sodium acetate-HCl buffer solutions at 60 °C, Rhodamine B exhibited a strong fluorescence peak at 584 nm using an excitation wavelength of 548 nm. The fluorescence quenching occurred when Fe₃O₄ nanoparticles catalyzed H₂O₂ oxidation of Rhodamine B. Under the chosen conditions, the fluorescence intensity at 584 nm decreased when the concentration of H₂O₂ increased. The fluorescence quenching intensity is linear with the concentration of H₂O₂ in the range of 10–200 nmol/L. Thus, a new and simple and sensitive nanocatalytic fluorescence method was proposed for the determination of H₂O₂ in synthetic sample, with satisfactory results.     

Europium-sensitized Chemiluminescence of System Tetracycline–H<Subscript>2</Subscript>O<Subscript>2</Subscript>–Fe(II)/(III) and Its Application to the Determination of Tetracycline

Chemiluminescence (CL) of the reaction system tetracycline–H₂O₂–Fe(II)/(III)–Eu(III) was used for the determination of tetracycline hydrochloride in water, pharmaceutical preparations, and honey. The CL spectrum registered for this system shows emission bands typical of Eu(III) ions, with a maximum at λ ∼ 600 nm, corresponding to the electronic transitions of ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂. A strong chemiluminescence intensity characteristic of europium(III) ions in the system tetracycline–H₂O₂–Fe(II)/(III)–Eu(III), as contrasted to the emission of the system tetracycline–H₂O₂–Fe(II)/(III) without Eu(III), proves that the Eu(III) ion plays the role of a chemiluminescence sensitizer, accompanying tetracycline oxidation in the Fenton system (H₂O₂–Fe(II)/(III)). A linear dependence was observed for the integrated CL light intensity on the tetracycline concentration in the range of 2 × 10⁻⁷ to 3 × 10⁻⁵ mol l⁻¹ with the detection limit of 5 × 10⁻⁸ mol l⁻¹ in aqueous solution.     

Broom-like and flower-like heterostructures of silver molybdate through pH controlled self assembly

Silver molybdate microrods are self-assembled into micron sized, broom-like and flower-like structures. Our investigations indicate that through a simple hydrothermal process, large scale production of such structure is possible. Using ammonium molybdate and silver nitrate solutions as precursors, we were able to show that the self assembled architectures were dependent on the pH of the starting precursor material. To understand the formation and destructions of the flower-like morphology, a systematic broad range (from acidic to basic) of pH-controlled experiments were performed and its influence on the structure/microstructure of synthesized materials was investigated. Scanning electron microscopy studies revealed that the morphology and microstructure of the products varied significantly by changing pH values from 3 to 8 during mixing of the reactants. pH = 3 and 4 resulted in the self assembly of monoclinic Ag₂(Mo₂O₇) microrods into broom-like structures, whereas pH = 5 resulted into the flower-like morphology of mixed phase of monoclinic and triclinic Ag₂Mo₂O₇. We also found that increasing the pH after a certain threshold value (for example pH > 6) resulted in total collapse of the flower-like morphology. Further increase of the pH to 7 and 8 resulted, the formation of microparticles of Ag₂MoO₄. A tentative scheme based on the pH-driven evolution of the self-assembly has been given to explain the formation of the observed heterostructures. Preliminary electrical characterization of thin films of the flower-like structures rendered non-linear current–voltage (I–V) responses. We also observed a strong hysteresis in the I–V responses of the flower-like structures developed under high bias conditions.     

A New Enhanced Oscillating Chemiluminescence System with Increased Chemiluminescence Intensity and Oscillation Time

Oscillating chemical reactions are complex systems, involving a large number of chemical species. In an oscillating chemical reaction, some species, usually a reaction intermediate, exhibit fluctuation in its concentration. In this report, oscillating chemiluminescence produced by the addition of thiosemicarbazide (TSC) to the oscillating system H₂O₂–KSCN–CuSO₄–NaOH was investigated using luminometry method. The effects of complexing agents, triethylenetetramine (TETA) and D-penicillamine, on the behavior of the oscillating system were investigated. Moreover, the influence of non-aqueous solvents, dimethyl sulfoxide (DMSO), nitromethane and acetonitrile, was studied. In the presence of solvents with high protophility, the chemiluminescence (CL) intensity was increased (sevenfold), the light emitting and oscillating time was enhanced by threefold. In addition, the effect of presence of non-ionic, cationic, and anionic surfactants was investigated. Non-ionic surfactant increased the intensity of the oscillating CL reaction by 4.5-fold.     

Luminescence of praseodymium (III) in solutions of mixed-ligand complexes with β-diketones

We have found that it is possible to enhance the luminescence of Pr(III) in solutions of complexes with β-diketones: acetylacetone derivatives containing fluoroalkyl substituents of different lengths and structures. We have established that in the presence of organic solvents, second (additional) ligands, and surfactants shielding the central ion from the quenching effect of the water molecules (OH oscillators), the intensity of luminescence for Pr(III) increases by a factor of 65, 38, and 45 respectively. In this case, cationic surfactants form ionic associates with Pr(III) β-diketonates, with incorporation of one more β-diketone molecule (ratio Pr:β-diketonate:surfactant = 1:4:1). As a result of suppression of intramolecular energy losses in solutions of Pr(III) β-diketonates, it is possible to observe its rather intense luminescence at 605 nm (the transition ¹D₂ → ³H₄), 612 nm (³P₀ → ³H₆), and 646 nm (³P₀ → 3F₂). __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 746–750, November–December, 2006.     

Analysis of the latent structure of luminescence and absorption spectra of thallium complexes

Comprehensive investigations of luminescence, excitation, and absorption spectra as well as of the luminescence kinetics of a frozen LiCl-Tl⁺ solution are carried out. It is established that the luminescence spectrum consists of four components. One component is caused by luminescence of the matrix and the remainder by luminescence of one luminescence center, namely, by the saturated complex of thallium TlCl₂(H₂O)Cl₄. The absorption spectrum consists of three components. Their parameters have been evaluated. Each component of the luminescence spectrum is excited in several components of the absorption spectrum. It is found that the luminescence spectrum components and their intrinsic absorption bands are located differently on the frequency axis. These data are similar to those obtained for other activated solutions of electrolytes. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 75–78, January–February, 2000.     

Spectroscopic and photoluminescence studies on optically transparent magnetic nanocomposites based on sol–gel glass: Fe3O4

Sol–gel glasses with Fe₃O₄ nanoparticles having particle sizes laying in the range 10–20 nm were encapsulated in the porous network of silica resulting in nanocomposites having both optical and magnetic properties. Spectroscopic and photoluminescence studies indicated that Fe₃O₄ nanocrystals are embedded in the silica matrix with no strong Si–O–Fe bonding. The composites exhibited a blue luminescence. The optical absorption edge of the composites red shifted with increasing concentration of Fe₃O₄ in the silica matrix. There is no obvious shift in the position of the luminescence peak with the concentration of Fe₃O₄ except that the intensity of the peak is decreased. The unique combinations of magnetic and optical properties are appealing for magneto–optical applications.     

Determination of the rate constant of oxygen quenching of the excited states of molecules from the singlet oxygen luminescence

We have pioneered a method of determining the rate constant of quenching of the excited electronic states of molecules by molecular oxygen from measurements of the kinetics of photosensitized luminescence of singlet molecular oxygen (^lδ_g). The method can be used in the case where the lifetime of the excited electronic state in an air-saturated solution is comparable with or larger than the luminescence time of the singlet molecular oxygen in the given solvent. It is shown that this situation is implemented on quenching, by molecular oxygen, of the excited triplet states associated with the biopolymers of tetrapyrrole molecules in aqueous (H₂O and D₂O) solutions. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 401–404, May–June, 2000.     

Ultrafine layered LiCoO2 obtained from citrate precursors

A new method for the preparation of ultrafine LiCoO₂ with a layered crystal structure was developed, which consists in thermal pyrolysis of homogeneous lithium-cobalt-citrate precursors. Atomic scale mixing of Li and Co is achieved by citric acid acting as a chelating agent. Electron spectroscopy of concentrated Li-Co-citrate solutions with Li:Co:Cit=1:1:1 and Li:Co:Cit=1:1:2 reveals that the predominant species at pH=7 are [Co(C₆H₅O₇)]⁻ and [Co(C₆H₅O₇)₂]⁴⁻ complexes. Freeze-drying of the two types of solutions leads to the formation of LiCo(C₆H₅O₇).nH₂O and (NH₄)₃LiCo(C₆H₅O₇)₂.nH₂O precursors, where Co²⁺ ions are complexed by one and two triionized citrate ions, respectively, and Li⁺ ions serve as counter ions. Between 400–600 °C, the thermal decomposition of these metal-citrate precursors yields LiCoO₂ with layered and pseudo-spinel structure, the proportion between them being depending on: (i) the Co/citrate ratio; (ii) the concentration of the freeze-dried solution; (iii) the heating rate. At 400 °C, the most defectless layered LiCoO₂, consisting of hexagonal individual particles with dimensions of 120–170 nm, is a product of the bis-citrate decomposition with a slow heating rate. For this sample, heating up to 600 °C does not affect the crystal size dimensions. For ultrafine layered LiCoO₂ and LiCoO₂ obtained by solid state reaction at high-temperatures (850 °C), the deintercalation and intercalation reactions proceed in the 3.95 – 3.99 and 3.86 – 3.88 voltage intervals, respectively. For defect trigonal LiCoO₂, additional oxidation and reduction peaks at 3.7 – 3.8 and 3.4 – 3.5 V were observed. We did not succeed in preparing monophase LiCoO₂ with pseudo-spinel structure. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Sept. 14–21, 1996     

Luminescence Properties of Metal(II)-Diethyldithiocarbamate Chelate Complex Particles and Its Analytical Application

In a suitable pH buffer solutions, sodium diethyldithiocarbamate (DDTC) reacts with some divalence metal ions M(II) to form (M–DDTC) _n chelate complex nanoparticles, which exhibit different luminescence properties. There is a strongest luminescence peak at 470 nm for the Co(II)–DDTC system, three peaks at 330, 470, and 630 nm for the Cu(II)–DDTC system, three peaks at 420, 470, and 630 nm for the Cd(II)–DDTC system, four peaks at 350, 400, 435, and 470 nm for the Ni(II)–DDTC system, two peaks at 408 and 470 nm for the Pb(II)–DDTC system, two peaks at 415 and 470 nm for the Fe(II)–DDTC system. The different luminescence properties of (M–DDTC) _n chelate complex nanoparticles was explained. Under the optimal conditions, the luminescence intensity of (Co–DDTC) _n chelate complex nanoparticles at 470 nm (F _{470 nm}) is linear to Co(II) concentration in the range of 0.012–1.44 μg/mL. The detection limit is 0.0023 μg/mL. A novel luminescence method has been proposed for the determination of cobalt in Vitamin B₁₂ samples, with satisfactory results.     

Spontaneous and stimulated red luminescence of Lu2O3: Eu nanocrystals

The spectra of spontaneous and stimulated luminescence of Lu₂O₃: Eu (7 at %) nanopowders at different optical pumping intensities have been investigated. The obtained results—changes in the shape of the red luminescence spectra and in the lifetime of the ⁵ D ₀ excited state of Eu³⁺ ions—indicate the onset of superluminescence with an increase in the excitation power. It has been found that an increase in the optical pumping intensity leads to a decrease in the luminescence decay time of the Lu₂O₃: Eu (7 at %) phosphor in the stimulated luminescence regime and to an increase in the quantum efficiency of red luminescence with a maximum at 611 nm.     

Thermally stimulated luminescence of yttrium oxide in a transparent dielectric medium

The thermally stimulated luminescence of Y₂O₃ in contact with a dielectric is investigated. The measurements were carried out in an atmosphere of dry air, in glycerol, ethylene glycol, and water. Shifting of the spectrum of thermally stimulated luminescence and decrease in the luminescence intensity with an increase in the dielectric constant of the medium were revealed. A discussion of the results is presented. I. I. Mechnikov Odessa State University, 2, Dvoryanskaya St., Odessa, 270026, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 462–463, May–June, 1998.     

New sign of vacuum ultraviolet driven crystal growth in ternary oxide Zn 3 V 2 O 8 films

Ternary oxide Zn₃V₂O₈ films was successfully formed on glass substrates only by means of vacuum ultraviolet irradiation to the spin-coated metal–organic solutions. From Fourier transform infrared spectroscopy measurements, we confirmed that the crystal growth proceeded at metal–organic bond cleavage under VUV irradiation. The crystalline size of the obtained materials was estimated to be 1.5–2.5 nm. The prepared Zn₃V₂O₈ films clearly showed yellow luminescence, corresponding to a charge transfer transition in the VO₄ tetrahedra.     

Luminescence of Thin Bismuth Germanate Films Having the Structure of Eulitine and Benitoite

The luminescence and luminescence excitation spectra of thin films of Bi₄Ge₃O₁₂ and Bi₂Ge₃O₉ were investigated. The spectra were decomposed into elementary components by the Alentsev-Fok method. It has been established that the luminescence spectra of thin Bi₄Ge₃O₁₂ and Bi₂Ge₃O₉ films have a similar structure and that each contains three luminescence bands with maxima at 2.70, 2.40, and 2.05 eV and at 2.73, 2.40, and 1.95 eV, respectively. Comparison of the results obtained with the well-known results of investigation of the luminescence of Bi₁₂GeO₂₀ and Bi₂O₃ suggests that the luminescence in the compounds considered is caused by the radiation processes that proceed in structural complexes of similar configuration that contain the bismuth ion in the nearest oxygen environment. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 377–380, May–June, 2005.     

Anti-stokes luminescence of solid AgCl<Subscript>0.95</Subscript>I<Subscript>0.05</Subscript> solutions

An anti-Stokes luminescence band with λ_max = 515 nm of microcrystals of solid AgCl_0.95I_0.05 solutions excited by a radiation flux of density 10¹³–10¹⁵ quanta/cm²·sec in the range 600–800 nm at 77 K was detected. It is shown that the intensity of this luminescence and the frequency of its excitation depend on the prior UV-irradiation of samples. Analysis of the stimulated-photoluminescence spectra and the anti-Stokes luminescence excitation spectra of the indicated microcrystals has shown that to the centers of anti-Stokes luminescence excitation correspond local levels in the forbidden band of the crystals. These states are apparently due to the atomic and molecular disperse silver particles that can be inherent in character or formed as a result of a low-temperature photochemical process. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 738–742, November–December, 2005.     

Thermally stimulated luminescence of bismuth germanate ceramics with the benitoite,eulitine, and sillenite structures

Thermally stimulated luminescence (TSL) of Bi₂Ge₃O₉, Bi₄Ge₃O₁₂, and Bi₁₂GeO₂₀ and the primary components Bi₂O₃ and GeO₂ was studied under x-ray excitation. Thermal activation energies and frequency factors of trapping centers in the studied ceramics were determined. The relationships of TSL bands of the studied ceramics with maxima at 141–145 and 166–170 K and damage to the Ge sublattice and of TSL bands with maxima at 104–110 and 180–190 K and recombination processes in the Bi sublattice were demonstrated. Recombination processes causing luminescence upon nonequilibrium charge carrier release from trapping centers occur in structural complexes of similar configuration that contain the Bi ion in a nearest environment of O atoms. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 359–364, May–June, 2008.     

Radiative properties of organic molecules in strong photon fields

We have experimentally investigated the dependence of the luminescence intensity of ethanol solutions of 2-(4-pyridyl)-5-phenyloxazole on the intensity of the exciting radiation from an XeCl laser (λ_ex = 308 nm, τ_p = 10 nsec, E_ex=10²²–10²⁶ photons/cm²·sec). We discuss the measurement technique and possible reasons for the change in radiative properties of the investigated solutions under the given conditions. V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 69–74, April, 1997.     

Electrochromic properties of tungsten oxides synthesized from aqueous solutions

Tungsten oxides are known to exhibit interesting electrochemical properties. Ion insertion (Li⁺, H⁺) within the oxide network is highly reversible. It leads to a blue coloration and WO₃ thin films can be used as electrochromic layers in display devices or smart windows. Tungsten oxide thin films can be conveniently deposited from aqueous solutions of tungstic acid. However polytungstic acids are not stable and tend to precipitate into hydrated tungsten oxide WO₃⋅2H₂O. The condensation of polytungstic species can be chemically controlled by adding foreign ions in the solution. Precipitation is no more observed in the presence of H₂O₂. Peroxopolytungstic acids are formed in which chelating [O₂]²⁻ ligands prevent the formation of an oxide network. Such solutions are specially convenient for the deposition of optically transparent thin films. Mixed oxides WO₃-MoO₃ are obtained when condensation is performed in the presence of Mo⁶⁺ cations. This paper shows how the condensation of tungstic acid can be chemically controlled and describes the electrochemical properties of the films deposited from such solutions. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

Luminescence centers in Pb2Bi6O11 and Sn2Bi6O11 ceramics

We have studied the luminescence spectra and luminescence excitation spectra of Pb₂Bi₆O₁₁ and Sn₂Bi₆O₁₁ ceramics at 80 K. We have used the Alentsev-Fock to decompose the spectra into elementary components. We have established that the luminescence spectra of Pb₂Bi₆O₁₁ and Sn₂Bi₆O₁₁ ceramics contain three elementary bands each with maxima at 2.60, 2.32, 12.93 eV and 2.62, 2.30, 2.00 eV. Comparison of the data obtained with the results of a study of the luminescence spectra for a series of bismuth-containing oxide compounds suggest that luminescence of Pb₂Bi₆O₁₁ and Sn₂Bi₆O₁₁ is due to radiative processes in structural complexes containing a bismuth ion in a nearest-neighbor oxygen environment. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 597–600, September–October, 2006.