Time-resolved Luminescence Spectroscopy Research Articles

Influence of fluorinated chain length on luminescent properties of [formula omitted][formula omitted]-diketonate complexes

Five novel europium β-diketonate complexes containing a pyrazole fragment were investigated. The influence of the number of fluorine atoms in diketonate ligands on luminescent properties was analyzed. Luminescence intensity of Eu3+ complexes increases significantly when CH bonds with high oscillation energy are replaced with CF bonds with low oscillation energy as the efficiency of energy transfer is improved. Further extension of the fluorinated chain length results in a substantial decrease in non-radiative relaxation rates while the increase in luminescence decay rates is observed. The theoretical results elaborated in terms of Judd-Ofelt theory are in good agreement with the experimental data obtained by time-resolved luminescence spectroscopy.

Luminescence spectroscopy of excitons in Zn1−xNixO oxides

Abstracts The paper presents the results of the study of two narrow luminescence lines I1 and I2 at the energies of 3.339 and 3.393 eV respectively in solid-state solutions Zn1−xNixO. The method of time-resolved luminescence spectroscopy with sub-nanosecond time resolution upon XUV excitation allows us to make a comparative analysis of nature of discovered lines. We consider the origin of narrow lines I1 and I2 as a radiative recombination of different excitons in Zn1−xNixO: I1-line is Wannier-Mott exciton, I2-line – p-d charge-transfer exciton. Noticeable differences of Wannier-Mott and p-d exciton properties are thoroughly discussed.

Intramolecular deactivation processes of electronically excited Lanthanide(III) complexes with organic acids of low molecular weight

The luminescence of Lanthanide(III) complexes with different model ligands was studied under direct as well as sensitized excitation conditions. The research was performed in the context of studies dealing with deep-underground storages for high-level nuclear waste. Here, Lanthanide(III) ions served as natural analogues for Actinide(III) ions and the low-molecular weight organic ligands are present in clay minerals and furthermore, they were employed as proxies for building blocks of humic substances, which are important complexing molecules in the natural environment, e.g., in the far field of a repository site. Time-resolved luminescence spectroscopy was applied for a detailed characterization of Eu(III), Tb(III), Sm(III) and Dy(III) complexes in aqueous solutions. Based on the observed luminescence the ligands were tentatively divided into two groups (A, B). The luminescence of Lanthanide(III) complexes of group A was mainly influenced by an energy transfer to OH-vibrations. Lanthanide(III) complexes of group B showed ligand-related luminescence quenching, which was further investigated. To gain more information on the underlying quenching processes of group A and B ligands, measurements at different temperatures (77K≤T≤353K) were performed and activation energies were determined based on an Arrhenius analysis. Moreover, the influence of the ionic strength between 0M≤I≤4M on the Lanthanide(III) luminescence was monitored for different complexes, in order to evaluate the influence of specific conditions encountered in host rocks foreseen as potential repository sites.

Differentiation of black writing ink on paper using luminescence lifetime by time-resolved luminescence spectroscopy

The time-resolved luminescence spectra and the lifetimes of eighteen black writing inks were measured to differentiate pen ink on altered documents. The spectra and lifetimes depended on the samples. About half of the samples only exhibited short-lived luminescence components on the nanosecond time scale. On the other hand, the other samples exhibited short- and long-lived components on the microsecond time scale. The samples could be classified into fifteen groups based on the luminescence spectra and dynamics. Therefore, luminescence lifetime can be used for the differentiation of writing inks, and luminescence lifetime imaging can be applied for the examination of altered documents.

Aromatic Thioethers as Novel Luminophores with Aggregation-Induced Fluorescence and Phosphorescence.

Here we report on a novel system based on aromatic thioethers with unique luminescence properties. Fifteen different compounds were investigated in detail on their luminescence properties using UV/Vis absorption and steady-state and time-resolved luminescence spectroscopy. Excited state lifetimes as well as quantum yields were determined, and the toxicity towards HeLa cells was investigated. Besides X-ray analyses also quantum chemical calculations were performed to gain deeper insights in the unique behavior of this facile system. The studied compounds reveal remarkable fluorescence emission ranging from 437 to 588 nm as well as phosphorescence (up to 5 μs).

Processes of energy migration in mixed europium–lanthanum magnesium borate nanocrystals

ABSTRACTProcesses of excitation energy migration in europium magnesium borate nanocrystals at different concentrations of neodymium and lanthanum ions were investigated by steady-state and time-resolved luminescence spectroscopy. Energy migration in neodymium doped mixed europium–lanthanum magnesium borate nanocrystals is well fitted by ∼t0.33 dependence indicating one-dimensional transport to neodymium energy acceptors through europium chains. Variation of neodymium and lanthanum concentrations have shown that at room temperature excitation can migrate over the distances up to 100 nm that is comparable with the size of nanocrystal.

Origin of Bi3+–related luminescence in Gd3Ga5O12:Bi epitaxial films

Photoluminescence characteristics of Gd3Ga5O12:Bi single crystalline films with different Bi contents grown by the liquid phase epitaxy are studied by the steady-state and time-resolved luminescence spectroscopy methods in the 4.2–500K temperature range under excitation within the 3.8–6.0eV. No ultraviolet emission, which could be ascribed to the radiative decay of the triplet excited state of Bi3+, is observed. Only visible emission is shown to arise from the Bi3+–related luminescence centers. Both the intense 2.54eV emission and the weaker 2.46eV emission of Gd3Ga5O12:Bi are shown to be of exciton origin. We suggest that they are due to the radiative decay of an exciton localized around a single Bi3+ ion and a dimer {Bi3+–Bi3+} center, respectively. The characteristic parameters of the corresponding exciton states are determined. The photostimulated processes, resulting in the localized excitons formation under excitation in the Bi3+–related absorption bands, are discussed. Peculiarities of Gd3+–Bi3+ energy transfer processes in Gd3Ga5O12:Bi are investigated. The possibility of application of Bi3+–doped gadolinium gallium garnets in scintillation detectors and light emitting diodes is considered.

Complexing power of hydro-soluble degradation products from γirradiated polyvinylchloride: influence on Eu(OH)3(s) solubility and Eu(III) speciation in neutral to alkaline environment

Abstract The complexing power of hydrosoluble degradation products (HDPs) from an alkaline hydrolysis of a 10 MGy γ-irradiated polyvinylchloride is studied. The complexation of Eu(III), as an analogue of lanthanide and actinide radionuclides at their +III oxidation state for oxygen containing functions, is evidenced both from the increasing of Eu(OH)3(s) dissolution, and from a complexometric titration by time-resolved luminescence spectroscopy. The dissolution of Eu(OH)3(s) in a simplified alkaline solution (0.3 M KOH/0.1 M NaOH) increases moderately, but significantly, with the HDPs concentration. The luminescence signal of the supernatant clearly indicates the presence of several complexed Eu(III) species. Performing a complexometric titration of Eu(III) from pH 6 by alkaline HDPs shows the formation of two different species with increasing HDPs’ concentration and pH. Operational complexation constants – based on dissolved carbon concentration – are proposed. The analyses of the spectra and luminescence decays seem to confirm the presence of two different species.

The Sorption Processes of U(VI) onto SiO2 in the Presence of Phosphate: from Binary Surface Species to Precipitation.

The ternary system containing aqueous U(VI), aqueous phosphate and solid SiO2 was comprehensively investigated using a batch sorption technique, in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy, time-resolved luminescence spectroscopy (TRLS), and surface complexation modeling (SCM). The batch sorption studies on silica gel (10 g/L) in the pH range 2.5 to 5 showed no significant increase in U(VI) uptake in the presence of phosphate at equimolar concentration of 20 μM, but significant increase in U(VI) uptake was observed for higher phosphate concentrations. In situ infrared and luminescence spectroscopic studies evidence the formation of two binary U(VI) surface species in the absence of phosphate, whereas after prolonged sorption in the presence of phosphate, the formation of a surface precipitate, most likely an autunite-like phase, is strongly suggested. From SCM, excellent fitting results were obtained exclusively considering two binary uranyl surface species and the formation of a solid uranyl phosphate phase. Ternary surface complexes were not needed to explain the data. The results of this study indicate that the sorption of U(VI) on SiO2 in the presence of inorganic phosphate initially involves binary surface-sorption species and evolves toward surface precipitation.

Efficiency estimates and practical aspects of an optical Kerr gate for time-resolved luminescence spectroscopy

We report experience of assembling an optical Kerr gate setup at the Femtosecond Laser Center for collective use at the Institute of Physics of the National Academy of Sciences of Ukraine. This offers an inexpensive solution to the problem of time-resolved luminescence spectroscopy. Practical aspects of its design and alignment are discussed and its main characteristics are evaluated. Theoretical analysis and numerical estimates are performed to evaluate the efficiency and the response time of an optical Kerr gate setup for fluorescence spectroscopy with subpicosecond time resolution. The theoretically calculated efficiency is compared with the experimentally measured one of ~12% for Crown 5 glass and ~2% for fused silica. Other characteristics of the Kerr gate are analyzed and ways to improve them are discussed. A method of compensation for the refractive index dispersion in a Kerr gate medium is suggested. Examples of the application of the optical Kerr gate setup for measurements of the time-resolved luminescence of Astra Phloxine and Coumarin 30 dyes and both linear and nonlinear chirp parameters of a supercontinuum are presented.

Comparing the luminescence processes of YVO4:Eu and core-shell YVO4@YF3 nanocrystals with bulk-YVO4:Eu

Comparative analysis of bulk, non-coated and core-shelled nanocrystalline YVO4:Eu was performed by means of time-resolved luminescence and VUV excitation luminescence spectroscopy techniques. Nanocrystalline YVO4:Eu samples – both as-prepared and YF3 core-shelled – have been synthesized by means of a microwave-assisted synthesis in ionic liquids, which allows to obtain 10–12nm nanoparticles with high crystallinity. The results show noticeable differences between bulk and nanocrystalline YVO4:Eu in photoluminescence experimental data, which explains by influence of the nanocrystal surface. A YF3 core-shell layer around YVO4:Eu nanoparticles partially recovers the intensity of the Eu3+ emission. It is demonstrated that the Eu3+ luminescence recovery is achieved at the expense of the suppression of the intrinsic emission but not due to the passivation of surface loss centers in core-shelled nanocrystals. It is also shown that surface loss processes are the reason of the degradation of energy transfer efficiency from the host lattice to Eu3+ under high-energy excitations in vacuum ultraviolet spectral range.

Eu2+ Stabilization in YAG Structure: Optical and Electron Paramagnetic Resonance Study

A set of Eu-doped Y3Al5O12 (YAG) phosphors in the powder form was successfully synthesized by multiple-step solid-state reaction under the reducing Ar:5%H2 atmosphere. Their physical properties were investigated by means of X-ray diffraction, time-resolved luminescence spectroscopy, and electron paramagnetic resonance (EPR). Special attention was given to well-grounded confirmation of Eu2+ occurrence in the YAG structure. X-ray diffraction confirmed the presence of a major YAG phase in all samples. The influence of Eu concentration, form of doping (EuS, EuF2, or Eu2O3) and number/form of annealing steps was studied. Corresponding characteristics were measured and evaluated in a broad temperature range (8–800 K). The correlated measurements showed that the single Eu2+ ions stabilized in YAG in the yttrium position are responsible for the 440 nm emission. The corresponding lowest energy excitation band is situated at 300 nm, and the radiative lifetime of Eu2+ emission is about 500 ns. A phenomenological mod...

A G-quadruplex-selective luminescent iridium(III) complex and its application by long lifetime

BackgroundThe G-quadruplex motif has been widely used for the construction of analytical detection platforms due to its rich structural polymorphism and flexibility. Luminescent assays are often limited due to the interference from endogenous fluorophores in biological samples. MethodsTo address this challenge, a novel long lifetime iridium(III) complex 1 was synthesized and used to construct a G-quadruplex-based assay for detecting prostate specific antigen (PSA) in aqueous solution. PSA is a common biomarker in serum and used as a model for demonstration in this work. ResultsThe PSA assay has achieved a detection limit of 40.8pg·mL−1, and shows high selectivity towards PSA over other proteins. Additionally, the assay could function in diluted human serum by using time-resolved luminescent spectroscopy, with good linearity from 1 to 10ng·mL−1 of PSA, which is adequate to detect the PSA levels for physiological (<4ng·mL−1) and clinical (4–10ng·mL−1) applications. ConclusionsThe assay was successfully constructed. As revealed from time-resolved method, the long lifetime property of iridium(III) complex 1 plays an important role in distinguishing phosphorescence signals from short-life auto-fluorescence of human serum. General significanceLuminescent transition metal complexes offer several advantages over other widely used organic fluorophores, such as long phosphorescence lifetime, large Stokes shift and modular syntheses. In addition, the assay could work effectively in diluted human serum using time-resolved luminescent spectroscopy, it therefore could be potentially developed to monitor PSA in biological samples. This article is part of a Special Issue entitled “G-quadruplex” Guest Editor: Dr. Concetta Giancola and Dr. Daniela Montesarchio.

Tunable Eu2+ Emission in KxNa1-XLuS2 Phosphors for Circadian LEDs

Set of novel Eu2+-doped KxNa1-xLuS2 phosphors (where x = 0 – 1) was successfully synthesized in the form of transparent crystalline hexagonal platelets by chemical reaction under the flow of hydrogen sulfide. Their physical properties were investigated by means of X-ray diffraction, X-ray excited fluorescence, time-resolved luminescence spectroscopy and electron paramagnetic resonance. Special attention is given to photoluminescence emission spectra under the 395 nm and 455 nm excitation aiming to obtain white emission with tunable color temperature, which is desirable for circadian white LEDs construction. EPR method is employed to understand the Eu2+ incorporation and distribution in the KxNa1-xLuS2 hosts. CIE xy-coordinates are used to compare effects of different K/Na concentration in KxNa1-xLuS2 on resulting spectrum (Figure 1). The application potential of mentioned compounds in the field of white LED solid state lighting phosphors with tunable color temperature is thoroughly discussed. The realistic circadian light bulb is presented as well and its properties are addressed. Figure 1

Influence of hydroxybenzoic acids on the adsorption of Eu(III) onto α,γ-Al2O3 particles in mildly acidic conditions: A macroscopic and spectroscopic study

The influence of hydroxybenzoic acids (HAHn), namely p-hydroxybenzoic acid (4-hydroxybenzoic acid, HPhbH) and protocatechuic acid (3,4-dihydroxybenzoic acid, HProtoH2), on the adsorption of europium(III) onto α,γ-Al2O3 particles is studied as a function of acid concentration. After measuring the adsorption edge of the Eu(III)/α,γ-Al2O3 binary system, and using the previously studied binary component system Eu(III)/HAHn—Moreau et al. (2015) Inorg. Chim. Acta432, 81—, and HAHn/α,γ-Al2O3—Moreau et al. (2013) Colloids Surf. A435, 97—, it is evidenced that HPhbH does not enhance Eu(III) adsorption onto α,γ-Al2O3 in the Eu(III)/HPhbH/α,γ-Al2O3 ternary system. Conversely, HProtoH2 enhances Eu(III) adsorption onto α,γ-Al2O3 in the Eu(III)/HProtoH2/α,γ-Al2O3 ternary system. Adsorption of the acids are also found higher in the Eu(III)/acid/α,γ-Al2O3 ternary systems as compared with the corresponding binary systems assessing synergetic effects. For high HPhbH concentrations, a ternary surface species involving ≡AlOH surface sites, Eu(III), and PhbH– is evidenced by time-resolved luminescence spectroscopy (TRLS). However, in the Eu(III)/HProtoH2/α,γ-Al2O3 ternary system, chemical environment of Eu(III) is found to be very close to that in the Eu(III)/HProtoH2 binary system. Ternary surface species could not be evidenced in the Eu(III)/HProtoH2/α,γ-Al2O3 ternary system with TRLS because of the very short decay time of Eu(III) in the presence of protocatechuic acid.

Study of the defects in La3Ta0.5Ga5.5O14 single crystals

Defects that are formed during crystal growth pose a serious obstacle for potential application of La3Ga5.5Ta0.5O14 (LGT) as a laser or piezoelectric crystal. We have performed the study of the defects origin in LGT crystals grown in different atmospheres using optical, EPR and time-resolved luminescence characterization methods. The absorption bands detected in the transparency region at 290, 360 and 490nm (T=300K) demonstrate different dependence on crystal annealing in vacuum and air. EPR analysis demonstrated that the defects responsible for these bands are non-paramagnetic. X-ray irradiation results in hole trapping by oxygen ions thus forming O− centers perturbed by neighboring defects. New arguments in favor of the existence of TaGa(2) antisite defects in LGT are presented. The absorption bands at 255 and 290nm are related to oxygen vacancies localized at the different sites of crystal lattice. The absorption band at 360nm is related to cation vacancies (VGa3−orVLa3−). Time-resolved luminescence spectroscopy allowed to identify excitation processes responsible for the defect-related emission bands.

Time-gated down-/up-conversion emission of Ho–CeO2 and Ho, Yb–CeO2 nanoparticles

Herein, we report the luminescence properties of (1%) Ho and (1%) Ho, (20%) Yb–CeO2 nanoparticles, investigated by time-resolved luminescence spectroscopy at 300 and 80K temperatures. The emission was measured over a broad detection range, from visible (450nm) up to infrared (1500nm) with excitation ranging from 210 to 1000nm. The structural properties were characterized by X-ray diffraction, Raman, Diffuse Reflectance Optical and Diffuse Reflectance Fourier Transform Infrared spectroscopies. The up-conversion emission of Ho–CeO2 and Ho, Yb–CeO2 using excitation wavelengths of 646.6, 759, 918and 971nm, respectively, were described in terms of time-gated up-conversion emission and excitation spectra, as well as up-conversion emission decays. Under short gate/ short delay conditions, the contribution of the 5F3 and 5F5 energy levels to the red emission of Ho at 630–680nm could be separated. The role of CeO2 charge transfer band as a selective antenna sensitizer as well as back transfer of excitation from Ho to Yb was also discussed. The mechanisms involved in the up-conversion emission of Ho and Ho, Yb–CeO2 were interpreted as ground state absorption followed by excited state absorption and energy transfer, respectively. For Ho, Yb–CeO2, a tunable red to green up-conversion emission ratio from 0.5 to 3.6 was also observed by increasing the power density of ~4 to 48W/cm2 of a cw laser diode at 980nm.

Time-resolved luminescence spectroscopy of structurally disordered K3WO3F3 crystals

Three emission centers of exciton-like origin, with distinct relaxation time, emission and excitation spectra were revealed in K3WO3F3 and described taking into account its structural disordering. Low-temperature monoclinic phase of K3WO3F3 features few anion sites with mixed oxygen/fluorine occupancy per [WO3F3] octahedron. Therefore, different kinds of distorted octahedra form, providing different luminescence centers. The time-resolved luminescence spectroscopy technique was applied to distinguish these centers. The simultaneous thermal quenching of them above ∼200 K was qualitatively explained involving dynamic structural disorder of the compound. The energy transfer mechanism between centers was found and tentatively described by the diffusion of excitons. Apart from intrinsic luminescence, the PL of defect-related centers was discovered and the role of shallow charge carrier traps in the low-temperature persistent luminescence was revealed.

Tunable Eu2 + emission in KxNa1 − xLuS2 phosphors for white LED application

Set of Eu2+-doped KxNa1−xLuS2 phosphors (x=0–1) in the form of transparent crystalline hexagonal platelets was successfully synthesized by chemical reaction under the flow of hydrogen sulfide. Their physical properties were investigated by means of X-ray diffraction, X-ray fluorescence, time-resolved luminescence spectroscopy and electron paramagnetic resonance. Special attention was given to photoluminescence emission spectra under the 395nm and 455nm excitation aiming to obtain white emission with tunable color temperature. EPR method was employed to understand the Eu2+ incorporation and distribution in the KxNa1−xLuS2 hosts. CIE xy-coordinates were calculated to compare effects of different K/Na concentration in KxNa1−xLuS2 on resulting spectrum. The application potential of mentioned compounds in the field of white LED solid state lighting phosphors is thoroughly discussed.

Luminescence properties of hybrid associates of colloidal CdS quantum dots with J-aggregates of thiatrimethine cyanine dye

Luminescence properties of water-soluble hybrid associates of semiconductor colloidal CdS quantum dots (QDs) with average size of 2.5nm, 3.2nm, 4.2nm and J-aggregates of 3,3′-di-(γ-sulfopropyl)-4,4′,5,5′-dibenzo-9-ethylthiacarbocyanine betaine pyridinium salt (Dye) in gelatin were investigated using the methods of absorption, steady-state and time-resolved luminescence spectroscopy. The decrease in luminescence intensity of CdS QDs and increase in luminescence intensity of Dye J-aggregates were detected with increasing of Dye concentration. It was shown that curves of luminescence decay of CdS QDs are non-exponential. The decreasing of luminescence lifetime of CdS QDs with increasing of Dye J-aggregates concentration was observed. It was concluded that dynamic quenching due to non-radiative resonance energy transfer takes place. It was shown that overlap integral between luminescence spectra of CdS QDs and absorption spectra of Dye J-aggregates increases with the increase of average diameter of CdS QDs and luminescence decay of CdS QDs is accelerated. Energy transfer efficiency for all three sizes of QDs was more than 31%.