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Extrinsic lyoluminescence of aluminum induced by lanthanide chelates in alkaline aqueous solution
Abstract
Reactive Al/OH-�(aq) interface was studied and used as a source of chemical energy in the generation of chemiluminescence. The observed extrinsic lyoluminescence emission during dissolution of aluminum in an alkaline Tb(III) or Eu(III) chelate solution was clearly based either on 5D 4 - 7F J radiative transitions of Tb(III) or 5 D 0 - 7 F J transitions of Eu(III). In this process, these chelates were chemically excited via analogous one-electron redox pathways as known from extrinsic lyoluminescence of irradiated, electrolytically- or additively-colored alkali halides, and from hot electron-induced electrochemiluminescence. Calibration curves of Tb(III) chelates, peroxodisulfate and hydroxide
ions were linear over several orders of magnitude of concentration. In addition, the method seems to be suitable for relatively rough chemical measurements of the thicknesses of aluminum oxide films free from trapped charges.
... It is known that both aromatic moiety oxidation, and reductioninitiated pathway is energetically possible from the studies of hydrated electron induced chemiluminescence of Tb(III) chelates in the presence of appropriate oxidizing and reducing agents [22,51,61]. With this particular chelate ligand's aromatic moiety reduction potential is approximated to be equal to benzophenone one-electron reduction potential, i.e. ca. ...
... However, we are convinced that in the range of conditions between the TR-HECL anodic onset potential and anodic potential of maximum emission (4 Ve5 V vs. SHE), the charge transfer through F-and F þ -center band (Fig. 5) is at least important as hydroxyl radical generation from reduction of oxygen species, since the present chelate is in need of either a simultaneous or sequential presence of sufficiently strong reductant and oxidant with proper ratio of reducing and oxidizing equivalents [22,49,51,61]. We propose that here in the intermittent anodic pulse potential range each anodic pulse empties the trapped electrons from the anion vacancies (F-and F þ -center band) and induces surface hydroxyl groups of the oxide to be oxidized to hydroxyl radicals, which are now in this pulse potential range probably the most significant primary oxidants. ...
... In spite of this, measured LL intensity profiles exhibit maxims in 1.3 µm region due to the heterogeneous solvent -solid substance interactions during the dissolution of irradiated sample or surface effects on radiation damage. The second of both mentioned possibilities was pointed out in [11] discussing the influence of single crystal surface upon formation of radiation in irradiated alkali halides as well in inorganic salts [12][13][14][15][16][17][18][19][20][21][22]. Direct micro spectrophotometric measurements of radiation damage profiles of accelerated ions LiF [7] also indicates increased concentration of F and F3 centres in the surface region. ...
Interaction of charged particles – protons, nitrogen, oxygen and carbon ions with LiF single crystals were studiedusing lyoluminescence method. Obtained linear energy transfer profiles were compared with those onescalculated by Monte Carlo method. The shape of the calculated and measured profiles was found to becomparable with Brag’s curve. Analyses of differences in shape of calculated and experimentally measuredcurves were performed. It is demonstrated that by gradually dissolving the crystal in the form of a disk, rotatingit with constant angular rate around its axis of symmetry, it is possible to determinate the defect distribution overthe crystal depth with a resolution of the order of 1μm according to measurements of lyoluminescence intensity.Also, a good precision of lyoluminescence intensity measurement and agreement of experimental energy lossprofiles with the theoretical ones are noted. Significant deviations from calculated profiles were observed indistances closer than 10-6 m to solid surface.
Chemiluminescence (CL) produced directly or indirectly as a result of electrochemical reactions is known as electrochemiluminescence (ECL), which is from the family of spectro-electrochemical techniques. For better understanding of ECL, various luminescence phenomena, particularly photoluminescence (PL), CL, and ECL, are briefly introduced. A brief ECL research background and theoretic basics of ECL are also described.
The reactivities of lanthanide ions in their excited states are first considered in water and the energy diagrams of most important of them are sketched to illustrate the highly oxidizing and reducing species involved reacting with one-electron steps. Anomalous photoluminescence behavior of Tb(III) chelated by 2,6-bis[N,N-bis(carboxymethyl)aminomethyl]-4-benzoylphenol is studied. The present chelate is known to show relative strong chemiluminescence in the presence of hydrated electron and oxidizing radicals but it shows an extraordinarily short luminescence lifetime of radiative relaxation of its 5D4 state under photoexcitation.
In this chapter, we discuss the basics of cathodic hot electron-induced electrogenerated chemiluminescence (HECL). In the
applications of HECL, we discuss, e.g., the usable electrode materials and their advantages as well as the applicable solution
conditions in aqueous media. We also summarize the luminophore types excitable by this method and their usability as labels
in practical bioaffinity assay applications.
The fundamentals of electrogenerated chemiluminescence (ECL), its unique features as compared to other luminescence, and mechanisms of its several types have been covered including a review of new developments in the field of instrumentation and luminophores and applications with emphasis on the detection and determination of biorelated species. ECL is proven to be a powerful tool for ultrasensitive biomolecule detection and quantification. The miniaturized biosensors based on this technology is capable of multiplexing detection with high sensitivity, low detection limit, and good selectivity and stability.
The temperature and mass dependence of lyoluminescence intensity of γ-irradiated colored potassium chloride powder have been studied using a photomultiplier tube connected to an x-y recorder. The peak lyoluminescence intensity increases with increasing amount of solute added up to 50 mg and then tends to saturate. The lyoluminescence (LL) glow curves with mass of KCl microcrystals show that initially the LL intensity increases with time and then decreases exponentially with time. The decay time consists of two components for all the masses. The dependence of decay time, especially the longer component on mass, has been investigated. The temperature dependence of LL intensity shows that initially the peak LL intensity increases with temperature up to 60°C, and then decreases with further increase in temperature. The decay time tends to decrease with increasing temperature. An explanation for the experimental results has been attempted.
A new electrogenerated chemiluminescence (ECL) reaction which utilizes tripropyl amine and Ru(bpy)32+ is presented The mechanism of light generation appears general enough to include a range of amines and luminophores. An oxidative-reduction mechanism is proposed. Upon electrochemical oxidation of both the luminophore and amine, a strong emission is observed. Voltammetric analysis reveals the potential for greatest light emission at the tripropyl amine oxidation. The emission is from the excited state of Ru(bpy)32+. An electron transfer reaction from the deprotonated tripropyl amine radical and Ru(bpy)33+ is the central reaction for excited state production. An estimate of the ECL efficiency cannot be made, due to the complex nature of the reaction.
Following the discovery of the hydrated electron in radiation chemistry, the reexamination of some fields of aqueous chemistry gave rise to a new concept of primary reduction processes. This paper surveys aspects of these investigations in which it appears that e⁻aq, as opposed to its conjugate acid (H atom), is invariably the precursor to H2 when water is reduced. Evidence is reviewed for the production of e⁻aq, (a) photochemically, (b) by chemical reduction of water, (c) electrolytically, (d) by photo-induced electron emission from metals, (e) from stable solvated electrons, and (f) from H atoms. The basis of standard electrode potentials and various aspects of hydrated electron chemistry are discussed briefly.
This chapter discusses the reduction potentials involving inorganic free radicals in aqueous solution. Because free radicals are usually transients, knowing their thermodynamic properties is primarily useful in mechanistic studies. Thus, the useful redox couples associated with a given free radical correspond to plausible elementary steps in reaction mechanisms. All potentials are expressed against the normal hydrogen electrode (NHE). Apart from the NHE, the standard state for all solutes is the unit molar solution at 25 °C. This violates the usual convention for species, such as O2 that occur as gases, but because the rates of bimolecular reactions in solution are significant, the unit molar standard state is most convenient. The emphasis is on electron transfer reactions in which no bonds are formed or broken, electron transfer reactions in which concerted electron transfer and bond cleavage could occur, and certain atom transfer reactions. The chapter also presents a tabulation of ∆fG° values for all the radicals. A common approach in estimating the thermochemistry of aqueous free radicals is to use gas-phase data with approximations of solvation energies.
The viability of X-ray irradiated sodium chloride as the excitation source to generate the radiative 5D4 → 7Fj transitions of chelated terbium(III) is demonstrated. The dissolution of X-ray irradiated sodium chloride in an aqueous solution produces a dynamic solid/solution interface containing hydrated electrons and dissolution-uncovered holes as strong one-electron reducing and oxidizing intermediates, respectively, which provides the energetic basis to initiate the sensitized Tb(UI)-specific extrinsic lyoluminescence of X-ray irradiated sodium chloride by the ligand-oxidation-initiated reductive and/or ligand-reduction-initiated oxidative excitation pathways. Redox luminescence mechanisms of Tb(III) chelates containing phenol, aniline or hydroxybenzophenone derivatives as their chemical energy-accepting aromatic moieties are discussed in detail.
Kinetic data for the radicals H⋅ and ⋅OH in aqueous solution,and the corresponding radical anions, ⋅O− and eaq−, have been critically pulse radiolysis, flash photolysis and other methods. Rate constants for over 3500 reaction are tabulated, including reaction with molecules, ions and other radicals derived from inorganic and organic solutes.
Electrochemical studies have shown that the reduction of persulfate and hydrogen peroxide is a two step mechanism, the first step occurs by electron transfer with the conduction band and the second step by hole injection with the valence band. It could be concluded from corresponding measurements performed with a semiconductor electrode that the electrochemical properties of these oxidizing agents have to be described by two instead of one redox (normal) potential. One normal potential is much lower and the other much larger than the theoretical value determined from thermodynamic data. These values are estimated as and .
Short-lived solid/solution interfaces, which are sufficiently energetic to initiate the radiative 3MLCT-based transition of rutheniumdl) tris-(2,2'-bipyridine) chelate, can be produced by dissolving x-ray irradiation colored or electrolytically colored alkali halides in water. This study discusses in detail the mechanisms of these ruthenium(II) tris-(2,2'-bipyridine)-specific extrinsic lyoluminescences of x-ray irradiated sodium chloride and electrolytically colored potassium chloride and, in addition, points out its analytical feasibility; air-equilibrated sample solutions can be used because of a weak quenching effect of dissolved oxygen on the Ru(bpy)2+3-specific lyoluminescences, calibration curves with linear ranges of 5 orders of magnitude and with the detection limits of approximately 1 × 10−10 M have been obtained for the Ru(bpy)2+3 determinations by using the aforementioned lyoluminescence excitation sources. In particular, the electrolytically colored potassium chloride in the presence of peroxydisulfate provides the excitation source for the ultimate trace analysis of ruthenium(II) tris-(2,2'-bipyridine) in aqueous solutions, mainly because of its good long term stability, and low inherent intrinsic lyoluminescence which results in a good signal-to-noise ratio for this lyoluminescent detection.
Dissolution of an additively coloured alkali halide crystal in an aqueous peroxydisulphate solution results in the formation of hydrated electrons and sulphate radicals. These radicals are capable of inducing terbium(III) chelate chemiluminescence by fast subsequent redox reactions, where the radiative 5D4 → 7Fj transitions of coordinated terbium(III) is based on a chemical excitation of the aromatic ligand by its interactions with these radicals, which is followed by an intramolecular transfer of this excitation energy to the 5D4 state of terbium(III).
An automatic system for measuring electroluminescence spectra is described. The instrument works in photon counting mode to record low-intensity light. Wavelength separation is done by a rotating interference filter. The instrument is controlled by a microprocessor, and is capable of generating arbitrary pulse wave-forms for the excitation of electroluminescence. The temporal variation of the spectra can be recorded at millisecond timescale. Application to electrogenerated chemiluminescence of luminol and fluorescein is shown.
Model systems for the photocatalyzed water reaction which explains the role of a sacrifical organic electron donor to drive the series of reactions leading to hydrogen production have been proposed. Studies which clarify the role of pH, mediator potential and EDTA oxidation rate in such systems where metal colloid catalysts such as tin(bipyridyl) ruthenium (II) are used to catalyze the photoreduction of water are reported. An optimum pH of 6 to 7 was observed for the hydrogen quantum yield. A series of homologous electron-transfer quencher mediators listed in a table were synthesized and characterized for use in the Hâ-generation system. All the mediators efficiently quenched the ruthenium excited state; and after the electron-transfer properties of the mediators had been characterized, the effect of the driving force on Hâ yield was studied. A clean linear yield relationship betwen quantum yield of hydrogen and driving forces for water reduction was observed. The same pH dependence of Hâ rate was seen in an electrochemical system in which neither amine nor ruthenium was present as with the ruthenium complex present. The rate of EDTA reduction decreased over 200 fold between pH7 and pH4. (BLM)
Rate constants have been compiled for reactions of various inorganic radicals produced by radiolysis or photolysis, as well as by other chemical means in aqueous solutions. Data are included for the reactions of ⋅CO2−, ⋅CO3⋅-, O3, ⋅N3, ⋅NH2, ⋅NO2, NO3⋅, ⋅PO32-, PO4⋅2-, SO2⋅ -, ⋅SO3 -, SO4⋅-, ⋅SO5⋅-, ⋅SeO3⋅ -, ⋅(SCN)2⋅ -, ⋅CL2⋅-, ⋅Br2⋅ -, ⋅I2⋅ -, ⋅ClO2⋅, ⋅BrO2⋅, and miscellaneous related radicals, with inorganic and organic compounds. © 1988, American Institute of Physics for the National Institute of Standards and Technology. All rights reserved.
One-electron reduction of oxygen, hydrogen peroxide, potassium peroxodisulphate and potassium peroxodiphosphate was studied during the dissolution of oxide-covered aluminum in alkaline aqueous solution. The production of free oxidizing radicals was monitored by luminol chemiluminescence (CL). It was observed superoxide, hydroxyl, sulphate and phosphate radicals can be generated by the present method. In addition, luminol can be detected below nanomolar level, the linear logarithmic calibration range covering several orders of magnitude of concentration. The metallic aluminum and low-valent aluminum ions are the primary reductants of the system. The electron transfer to the solution is proposed to occur by tunneling through a thin insulating aluminum oxide film at the solid/electrolyte interface in moderately alkaline solutions with simultaneous dissolution of the forming oxide film. In a highly alkaline solution, it is more probable that the oxidation of aluminum species occurs in direct contact of the metallic aluminum with the aqueous solution. In the latter case, short-lived solvated low-valent aluminum ions, hydrogen atom and its deprotonated form, the hydrated electron, can exist as reducing mediators in the chemical reactions in the close vicinity of the dissolving solid/electrolyte interface. Luminol was also observed to exhibit CL under purely reducing conditions produced by a presently unknown excitation pathway.
Aromatic Gd(III) and Y(III) chelates produce ligand-centered emissions during cathodic pulse polarization of oxide-covered
aluminum electrodes, while the corresponding Tb(III) chelates produce metal-centered5D4 →7Fj emissions. It was observed that a redox-inert paramagnetic heavy lanthanoid ion, Gd(III), seems to enhance strongly intersystem
crossing in the excited ligand and direct the deexcitation toward a triplet-state emission, while a lighter diamagnetic Y(III)
ion directs the photophysical processes toward a singlet-state emission of the ligand. The luminescence lifetime of Y(III)
chelates was too short to be measured with our apparatus, but the luminescence lifetime of Gd(III) chelates was between 20
and 70 μs. The mechanisms of the ECL processes are discussed in detail.
The primary processes occurring at cathodically polarized oxide-covered aluminum electrode are discussed in detail. It is pointed out that more energetic cathodic processes can be induced in aqueous media at thin insulating film-coated electrodes than at any semiconductor or active metal electrode. It is proposed that tunnel emission of hot electrons with energies well above the level of the conduction band edge of water occur, and the thermalization and solvation of the emitted electrons can result in generation of hydrated electrons. The cathodically pulse-polarized oxide-covered aluminum also generates a strong oxidant (or oxidants) at the oxide/electrolyte interface, and it is proposed that this species is the hydroxyl radical which is generated either by cathodic high field-induced ejection of self-trapped holes as oxygen dianions (i.e. oxide radical ions) into the electrolyte solution, or by the action of anion vacancies and/or F+-centers as the primary oxidants capable of oxidizing hydroxide ions or the hydroxyl groups of the hydroxylated surface on the oxide film. These radicals, hydrated electrons/hydroxyl radicals, can act as mediating reductants/oxidants in reduction/oxidation of solutes. The formation of the primary species is monitored by electrochemiluminophores which cannot be cathodically excited at active metal electrodes in fully aqueous solutions, but which can be chemically excited in aqueous media in the simultaneous presence of highly reducing and highly oxidizing radicals.
The OO bond of solid potassium peroxodisulfate can be ruptured by UV irradiation, which results in a solid solution of sulfate radicals in potassium peroxodisulfate. The dissolution of this irradiated solid in water produces a solid/solution interface rich in hydrated sulfate radicals, which can either recombine to form peroxodisulfate ions, or react with solvent or solutes in a sample solution. In terbium(III)-containing aqueous solutions, this dissolution produces the characteristic radiative 5D4→7F-multiplet transitions of terbium(III). This study points out that the light-emitting pathway of this terbium(III) lyoluminescence consists of the following steps: (i) hydrated sulfate radical oxidizes terbium(III) to terbium(IV), (ii) terbium(IV) is immediately reduced by water via a process that is sufficiently energetic to leave the resulting terbium(III) in its lowest excited state 5D4 and finally, (iii) the relaxation of this excited 5D4 state of terbium(III) induces the aforementioned transitions. Thus, this terbium(III) lyoluminescence can be also classified as chemiluminescence. In addition, x-ray irradiated potassium peroxodisulfate is capable of generating an analogous terbium(III) lyoluminescence, which is, however, investigated only on qualitative basis. Lyoluminescence generation of both irradiated materials can be used to determine hydrated Tb(III) down to the micromolar level in aqueous solutions.
The term lyoluminescence refers to the light emitted when certain materials go into solution. The effect is enhanced in most materials if they have previously been exposed to ionizing radiation. Recent investigations have been directed toward applications to dosimetry, particularly at high doses. Both organic and inorganic phosphors exhibit the property, but the mechanism for light emission is different in detail for the two classes of materials. This review discusses the original and early work, as well as more recent investigations.
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