Luminescent and thermochromic properties of tellurium(IV) halide complexes with cesium

The spectral?luminescent and thermochromic properties of complex compounds of the composition Cs₂TeHal₆ (Hal = Cl, Br, I) are studied. The interrelation between the geometric structure and spectral–luminescent properties is studied using the example on complex compounds of tellurium(IV) halides with cesium. The Stokes shift and the luminescence intensity of Тe(IV) ions with island octahedral coordination are found to depend on the position of the A band in the luminescence excitation spectra, the diffuse reflection, and the energy of the luminescent ³P₁ → ¹S₀ transition of the tellurium(IV) ion. The maximum luminescence intensity and the minimum Stokes shift at 77 and 300 K are observed for Cs₂TeСl₆. The geometrical and electronic factors responsible for luminescence intensification in Te(IV) complexes under study are analyzed.     

Sensing Alkali and Alkaline Earth Metal Cations by Conduction Band Quenching of Dye Photoluminescence

A new luminescence approach for sensing alkali and alkaline earth metal cations in fluid solution at room temperature is described. The approach is to utilize surface-adsorption/desorption–induced energetic shifts of a semiconductor conduction band to alter the electron transfer quenching efficiency of a photoluminescent dye. A proof-of-concept example is described based on TiO₂ nanoparticles with a surface bound Ru(II) coordination compound as the dye, Ru(deeb)(bpy)₂(PF₆)₂ where deeb is 4,4-(CO₂CH₂CH₃)₂-2,2-bipyridine and bpy is 2,2-bipyridine, sensing alkali and alkaline earth metal cations in acetonitrile solution. The Ru(II) compound is highly luminescent with long excited state lifetimes in the absence of the cations but is quenched in their presence. The quenching is found to be reversible. The data demonstrate that this approach yields intensity, lifetime, and wavelength-ratiometric calcium ion sensors that are sensitive to 5 7 × 10^–4 M concentrations.     

Surface-enhanced luminescence from Eu 3+ complex nearby Ag colloids

The effect of colloidal dispersion of silver on the luminescent properties of Eu (III) complex with pyridine-3,5-dicarboxylic acid (PyDC) was investigated. The luminescence from Förster type europium complex was enhanced several times with the presence of Ag colloid and the enhancement factor showed Ag concentration dependence. The observed enhancement effect was discussed in view of surface-enhancement effect and optical absorption due to surface plasmon resonance, both arising from excitation of surface plasmon polariton. The coordination structure around Eu (III) ion was also affected with the presence of Ag colloid, which induced the change in the intensity ratio between two emission bands of ⁵ D ₀ ⁷ F ₁ and ⁵ D ₀ ⁷ F ₂ transitions of Eu (III) ion.     

Optical oxygen sensing materials based on trinuclear starburst ruthenium(II) complexes assembled in mesoporous silica

The preparation and oxygen sensing properties of optical materials based on two trinuclear starburst ruthenium(II) complexes: [Ru₃(bpy)₆(TMMB)]⁶⁺ (1) and [Ru₃(phen)₆(TMMB)]⁶⁺ (2) (bpy=2,2′-bpyridine, phen=1,10-phenathroline, TMMB=1,3,5-tris[2-(2′-pyridyl)benzimidazoyl]methylbenzene) assembled in two mesoporous silicate (MS) are described in this paper. The luminescence of Ru complexes/silicate assemble materials can be quenched by molecular oxygen with good sensitivity (I₀/I₁>5 for 2/MS and I₀/I₁>3 for 1/MS), indicating that trinuclear starburst Ru(II) complexes/MS systems are sensitive to oxygen molecules.     

Dithiane Based Boronic Acid as a Carbohydrate Sensor in an Aqueous Solution at pH 7.5: Theoretical and Experimental Approach

Carbohydrate sensing in an aqueous solution remains a very challenging area of interest. Using the idea of covalent reversible interaction between boronic acids and the diol groups in carbohydrates enable us to design a carbohydrate sensor 1-thianthrenylboronic acid (1T), which has high selectivity towards fructose. To elucidate the sensing and binding properties of 1T with sugars, we have incorporated theoretical (DFT and TD-DFT) and spectroscopic techniques. For an optimized geometry, the complete vibrational assignments were done with FT-IR and FT-Raman spectra. Physiochemical parameters were obtained by implementing frontier molecular orbital (FMO) analysis. Further, excited state properties were determined by performing TD-DFT calculations in solvent and these properties were in good agreement with the experiment. The steady state fluorescence measurements with varying concentration of sugars, revealed that the fluorescence intensity of boronic acid is enhanced by studied sugars due to the structural modification. We also noticed remarkable changes in fluorescence lifetimes and quantum yield after adding sugars. The article also reports influence of pH on boronic acid’s fluorescence intensity with and without sugars. The fluorescence of boronic acid increases with the increase in pH. These changes are due to acid–base equilibrium of boronic acid and led us to estimate the pKa value of 7.6. All the theoretical and experimental evidences suggested that 1T can be used as a possible fluorescent sensor for fructose. In addition, 1T showed very good affinity for Cu²⁺ ion with K_a?=?150?×?10² M^?1, which suggests that 1T can also be used as a chemosensor for Cu²⁺ ions.

     

A Glucose Sensing Contact Lens: A Non-Invasive Technique for Continuous Physiological Glucose Monitoring

We have developed a range of glucose sensing contact lenses, using a daily, disposable contact lens embedded with newly developed boronic acid containing fluorophores. Our findings show that our approach may be suitable for the continuous monitoring of tear glucose levels in the range 50–1000 M, which typically track blood glucose levels, which are 5–10 fold higher. Our non-invasive approach may well offer an alternative solution to current invasive glucose monitoring techniques for diabetes, such as finger pricking.     

Optical Properties of Semiconducting Ruthenium Silicide

The optical properties of ruthenium silicide Ru₂Si₃ have been studied theoretically and experimentally. The energy band spectrum and optical properties were simulated with the aid of the firstprinciple selfconsistent method of linear attached plane waves. The spectral dependence of the absorption coefficient in the 0.52.2 eV energy range was measured experimentally by the photothermal refractive spectroscopy method. It is established that ruthenium silicide is a directgap semiconductor having an energy gap of 0.84 eV and a low oscillator strength of the first direct transition.     

Sensitization of Luminescence of Europium Compounds on Solid Matrices by Terbium (III) Ions

The conditions of sensitization of the luminescence of Eu(III) by Tb(III) ions in complexes with inorganic (Na₂WO₄) and organic (nalidixic acid) ligands in sorbates on solid matrices (zeolite CaX and crystalline zirconium phosphate (ZrP)) and in coprecipitation with CaWO₄ have been investigated. It has been established that the maximum sensitization of the europium luminescence is attained in the case where Eu and Tb are present in a 1:0.5 ratio. In this case, the integral intensity of luminescence of Eu(III) (the band with _max = 612 nm) in the sorbate of its complex with nalidixic acid on ZrP accounts for more than 60% of the luminescence intensity of the industrial photoluminophor Y₂O₃:Eu (FL-612) possessing red luminescence, and the intensity of Tb(III) luminescence (the band with _max = 545 nm) accounts for about 40% of the luminescence intensity of the photoluminophor Gd₂O₂S:Tb possessing green luminescence.     

Design and Synthesis of a Ruthenium(II) Complex-Based Luminescent Probe for Highly Selective and Sensitive Luminescence Detection of Nitric Oxide

Nitric oxide (NO) is one of the most important intercellular signaling molecules, and plays important roles in various biological systems. In this work, a unique Ru^II complex, tris[(5-(4-methylamino-3-aminobenzylamino)-1,10-phenanthroline)] ruthenium(II) hexafluorophosphate [Ru(MAA-phen)₃][PF₆]₂, has been designed and synthesized as a luminescent probe for the detection of NO in aqueous media. The complex itself is almost non-luminescent, but can specifically react with NO under the aerobic conditions to afford its highly luminescent triazole derivative in aqueous media, [Ru(MTA-phen)₃]²⁺ (MTA-phen: methyl-trazolebenzylamino-1,10-phenanthroline), accompanied by a 302-fold increase in luminescence intensity at 598 nm with a 130 nm Stokes shift. The luminescence response of [Ru(MAA-phen)₃]²⁺ to NO is rapid, highly specific without interferences of other reactive oxygen/nitrogen species, and highly stable against the pH changes in the range of pH 4.5–9.5. These features enable [Ru(MAA-phen)₃]²⁺ to be used as a probe for the highly selective and sensitive luminescence detection of NO in weakly acidic, neutral, and weakly basic media.     

A facile synthesis approach and impact of shell formation on morphological structure and luminescent properties of aqueous dispersible NaGdF<Subscript>4</Subscript>:Yb/Er upconversion nanorods

A general facile synthesis approach was used for fabrication of highly emissive aqueous dispersible hexagonal phase upconversion luminescent NaGdF₄:Yb/Er nanorods (core NRs) through metal complex decomposition process. An inert NaGdF₄ and porous silica layers were grafted surrounding the surface of each and every NRs to enhance their luminescence efficiency and colloidal dispersibility in aqueous environment. Optical properties in terms of band gap energy of core, core/shell, and silica-coated core/shell/SiO₂ nanorods were observed to investigate the influence of surface coating, which was gradually decreased after surface coating because of increase crystalline size after growth of inert and silica shells. The inert shell formation before silica surface grafting, upconversion luminescence intensity was greatly improved by about 20 times, owing to the effective surface passivation of the seed core and, therefore, protection of Er³⁺ ion in the core from the nonradiative decay caused by surface defects. Moreover, after silica coating, core/shell nanorods shows strong upconversion luminescence property similar to the hexagonal upconversion core NRs. It is expected that these NaGdF₄:Yb/Er@NaGdF₄@SiO₂ (core/shell/SiO₂) NRs including highly upconversion emissive and aqueous dispersible properties make them an ideal materials for various photonic-based potential applications such as in upconversion luminescent bioimaging, magnetic resonance imaging, and photodynamic therapy.

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Graphical abstract ?

     

Non-injection and one-pot approach to CdSe: Eu<Superscript>3+</Superscript> hybrid nanocrystals with tunable photoluminescence from green to red

Europium ion-doped CdSe hybrid nanocrystals (CdSe:Eu³⁺ NCs) as a class of new luminescent materials have drawn increasing attention in recent years owing to their remarkable optical properties. In this paper, we report a facile method to prepare CdSe:Eu³⁺ NCs using oleic acid (OA) as the capping agent. With this non-injection and one-pot synthesized approach, the formation and surface passivation of CdSe:Eu³⁺ NCs are performed simultaneously and result in intrinsic luminescence. The as-prepared CdSe:Eu³⁺ NCs are characterized by transmission electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy (EDX). Their optical properties are also studied by UV–vis and photoluminescence spectra. Moreover, the effects of feed ratios and reaction temperatures on the optical properties are further investigated. The results show that the luminescent spectra of CdSe:Eu³⁺ NCs are tunable from green (490 nm) to red (630 nm) and gradually redshift with the increase of the nanoparticle size from 2.5 to 4.4 nm. Upon decoration with 2-thenoyltrifluoroacetone (TTA), the luminescence of europium ion drastically increases and efficient energy transfer from CdSe host to the europium ion is proposed. In addition, an MTT and apoptosis assay show CdSe:Eu³⁺ NCs have low cellular toxicity and could be used as fluorescence imaging for human epithelial type 2 (Hep-2) cells. These properties make CdSe:Eu³⁺ NCs a potential candidate for biological labeling, immunoassays, and optical sensing.

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Graphical abstract Stable and luminescent CdSe:Eu³⁺ hybrid nanocrystals were synthesized, and the luminescence is tunable from green to red by the variation of reaction temperatures and feed ratios. Moreover, CdSe:Eu³⁺ NCs show low cellular toxicity and could be used as fluorescence probes for Hep-2 cells.

     

Tripolyphosphate as Precursor for REPO4:Eu3+ (RE = Y, La, Gd) by a Polymeric Method

A modification of the Pechini method was applied to obtain luminescent rare earth orthophosphates. The developed synthetic route is based on the ability of the tripolyphosphate anion () to act both as a complexing agent and as an orthophosphate precursor. Heating of aqueous solutions containing RE³⁺, Eu³⁺, , citric acid, and ethylene glycol led to polymeric resins. The ignition of these resins at different temperatures yielded luminescent orthophosphates. The produced nanosized phosphors (YPO₄:Eu³⁺, (Y,Gd)PO₄:Eu³⁺, and LaPO₄:Eu³⁺) were analyzed by infrared and luminescence spectroscopies, X-ray diffractometry, and scanning electron microscopy.     

Potassium Sensing by Using a Newly Synthesized Squaraine Dye in Sol-Gel Matrix

Squaraines are a group of fluorescent dyes and pigments derived from squaric acid and dialkylanilines well known in applications such as photoreceptors, organic solar cells, optical recording media, and non-linear optics. Their very promising spectral properties, long wavelength absorption and emission, and high absorptivity and quantum yields have not been exploited so far in relation to optical sensor design. They exhibit excellent solubility in sol-gel matrices, and the ligand is an integral part of the fluorophore system, which makes the molecule a fluoroionophore. In this work, potassium-sensing agent, bis[4-N-(1-aza-4,7,10,13,16-pentaox acyclooctadecyl)-3,5-dihydroxyphenyl] squaraine has been used for potassium sensing in a sol-gel matrix. The spectrofluorimetric response of dye-doped tetraethyl ortosilicate (TEOS) film after exposure to certain concentrations of K⁺ has been investigated, and 62% of relative signal change was achieved. The dynamic working range of the sensor membrane has been found between 10^–9 and 10^–6 M K⁺, in other terms from nanomolar to micromolar levels, which is an advantage over flame emission spectroscopy, in view of detection limit. The sensor is fully reversible within the dynamic range and the response time (₉₀) is found to be 2 min under batch conditions. The cross-sensitivity of the molecule to Na⁺, Ba²⁺, Ca²⁺, and NH⁺ ₄ was also tested in separate solutions.     

Spectral studies of Nd3+ and Er3+ ions in POCl3:SnCl4 laser liquid

The optical absorption spectra of triply ionized neodymium and erbium ions in POCl₃SnCl₄ laser liquid have been studied for the first time in the UV-VIS and NIR regions. Spectroscopic and Judd-Ofelt intensity parameters are evaluated from the observed band positions and their intensities. Radiative lifetimes and the luminescent branching ratios for the excited fluorescent levels of Nd³⁺ and Er³⁺ ions are theoretically estimated and the possible laser transitions are indicated. From the observed splittings of certain bands in the second-derivative spectrum of the Nd³⁺ ion, the crystal field (A ₂₀,A ₄₀) parameters are evaluated assumingC _3h symmetry for the ion.     

Specific solvent effects of hydroxylic solvents on the emission properties of ruthenium(ii)tris(2,2′-bipyridyl) chloride

The excited state of Ru(II)[bpy]₃ ²⁺ dissolved in hydroxylic solvents is subject to specific solvent effects, which were hitherto not understood on a quantitative basis. We determined the solvent effects of linear monovalent alcohols on the energy gap law of internal conversion with the help of lifetime and intensity measurements. An on-line method for measurement of the temperature dependence of quantum efficiencies was introduced. A modified Franck-Condon analysis of emission spectra by taking into account the shape of a Morse potential of the involved states was applied to compute excited-state energies.Abbreviations used Ru(II)[bpy]₃ ²⁺ ruthenium(II)tris(2,2-bipyridyl) chloride - MLCT metal-to-ligand charge transfer - PMT photomultiplier tube     

Photoluminescence and Optical Absorption of Cs2NaScF6:Cr3+

The main objective of this paper is the characterization of the spectroscopic properties of new materials that are prospective laser media. This approach allows for the comparison of the properties of the Cr³⁺ in different environments. Here, we have studied the photoluminescence and optical absorption of Cs₂NaScF₆:Cr³⁺ single crystals. On the basis of near-infrared luminescence measurements at 2, 77, and 300 K the observed lines originated from the Cr³⁺-centres were associated with the transition and the lifetimes were obtained. In spite of the quenching observed as a function of temperature at least 10% of the 2 K emission intensity for Cs₂NaScF₆ doped with 1% of Cr³⁺ remains at room temperature. Besides, the 2 K emission broad band could be well described in terms of normal modes of the octahedral complex [CrF₆]³⁻, and the Racah and crystal-field parameters calculated.     

Specific Features of Light Scattering in [N(CH3)4]2CuCl4 Crystals with an Incommensurable Phase

We present the results of investigation of the optical birefringence and intensity of the main light beam that passed through an [N(CH₃)₄]₂CuCl₄ crystal under the conditions of viscous interaction of the incommensurable structure with defects. A nonmonotonic temperature dependence of the basic signal is revealed. The observed temperature dependence of the intensity (in the form of irregular steps) is related to different periods of the incommensurable structure. In transitions between adjacent metastable states the periodicity of the incommensurable structure changes. It is shown that in transition regions for the central beam one observes an anomalous decrease in the light intensity due to the appearance of a perturbation lattice with the wave vector q.     

Optical evidence for the proximity to a spin-density-wave metallic state in $\mathsf{Na_{0.7}CoO_2}$

We present the optical properties of Na_0.7CoO₂ single crystals, measured over a broad spectral range as a function of temperature (T). The capability to cover the energy range from the far-infrared up to the ultraviolet allows us to perform reliable Kramers-Kronig transformation, in order to obtain the absorption spectrum (i.e., the complex optical conductivity). To the complex optical conductivity we apply the generalized Drude model, extracting the frequency dependence of the scattering rate ( ) and effective mass (m ^*) of the itinerant charge carriers. We find that at low temperatures and for . This suggests that Na_0.7CoO₂ is at the verge of a spin-density-wave metallic phase.Received: 6 August 2004, Published online: 9 September 2004PACS: 78.20.-e Optical properties of bulk materials and thin films - 74.70.Dd Ternary, quaternary and multinary compounds (including Chevrel phases, borocarbides, etc.) - 75.30.Fv Spin-density waves     

Crystal Structure,Luminescence and Triboluminescence of the Complex [Eu(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>3hmpa] NO<Subscript>3</Subscript>·HQuin

The atomic structure of crystals of the complex [Eu(NO₃)₂3hmpa] NO₃·HQuin , (hmpa – hexamethylphosphortriamide, HQuin – quinaldic acid) characterized by intensive luminescence and triboluminescence has been determined by the X-ray method. The noncentro-symmetric crystals of the compound are rhombic : a = 16.8193(3), b = 12.2877(2), c = 27.6516(5) Å, пр. гр. Pca2(1), Z = 4, ρ _{calc. .} = 1.427 g/сm³. The crystals have a structure of the insular type which is presented by the isolated complex molecules, outer-sphere NO₃ ^? – groups, and neutral molecules of quinaldic acid. Some structural aspects of formation of the luminescent and triboluminescent properties of the compound were discussed: the role of break planes in the crystal destruction was revealed.     

Effect of Zeeman Depopulation Pumping on Cycling Atomic Transitions

The results of an investigation of fluorescence signal at 6S_1/2 (F_g = 4) → 6P_3/2 (F_e = 5) transition of D₂ line of atomic Cs vapor versus the magnetic field (up to B = 90 G), directed along the linear polarization of exciting light are presented. The recorded reduction of fluorescence in the magnetic field, which is especially strong at high intensity of laser radiation, is explained by conversion of the Zeeman optical pumping (the alignment) into the depopulation pumping under conditions, when the Zeeman frequency shift of individual transitions between magnetic sublevels exceeds the homogeneous width of transition. In consequence, the cycling hyperfine transition F_g = 4 → F_e = 5 is transformed into an open one.