Luminescence quenching of complexes immobilized on a cation-exchange membrane by molecular oxygen

A technique is developed and luminescence quenching of complexes immobilized on cation-exchange membranes is considered. The mechanism of the luminescence quenching of the complexes by molecular oxygen is discussed.     

Quenching of luminescence of cyclometalated Pt(II) complexes by molecular oxygen

A method of studying the quenching of luminescence of cyclometalated ethylenediamine complexes of Pt(II) by molecular oxygen is developed. The bimolecular rate constants of quenching are determined.     

Quenching of luminescence by coloration in KI and RbI

Quenching of exciton luminescence caused by coloration with u.v. irradiation in KI and RbI has been studied. Luminescence intensity measured after coloration is found to show a remarkable dependence on temperature. A possible explanation is given for the mechanism of luminescence quenching on the assumption that the luminescence intensity is proportional to the probability of exciton self-trapping.     

Luminescence of AgHal phosphors containing a silver sulfide impurity

In a study of the luminescence spectra of AgHal single crystals containing various levels of a silver sulfide impurity, the mechanism for the luminescence is established. The thermal quenching of the steady-state luminescence and of the light sum of the luminescence of AgHal (Ag₂S) phosphors is due to ionic processes, as in pure silver halides. The activation energy for the thermal quenching of the light sum is found. The ratio of the cross sections for electron recombination with holes localized at the luminescence centers responsible for the various luminescence bands is found in a kinetic study of the decay of the optical emission stimulated in these bands.     

Surface State‐Induced Anomalous Negative Thermal Quenching of Multiferroic BiFeO3 Nanowires

Wide‐bandgap semiconductor nanowires with surface defect emission centers have the potential to be used as sensitive thermometers and optical probes. Here, we show that the green luminescence of multiferroic BiFeO₃ (BFO) nanowires shows an anomalous negative thermal quenching (NTQ) with increasing temperatures. The release of trapped carriers from localized surface defect states is suggested as the possible mechanism for the increased green luminescence which was experimentally observed at elevated temperatures. A reasonable interpretation of the photoluminescence (PL) processes in BFO nanowires is achieved, and the activation energies of the PL quenching and thermal hopping are deduced. Negative thermal quenching of BFO nanowires provides a new strategy for optical thermometry at higher temperatures.     

Static and dynamic quenching of luminescent species in polymer media

A method developed for quantitative determination of static and dynamic contributions to luminescence quenching is applied to Ru(II) complexes in polymer matrices (silica gel and polystyrene), quenched by oxygen. This method is based on both intensity and lifetime quenching experiments. The curvature of intensity Stern-Volmer plots is related to the results.     

The influence of the migration mechanism of approaching particles on the energy transfer between them

A way is proposed to experimentally solve the problem of the length of the jumps by which the particle diffusion in viscous solutions is realized. For that purpose it is necessary to measure the rate of impurity quenching of luminescence as a function of temperature and to choose among jumping, diffusion and mixed mechanisms of quenching. The measurements must be carried out at two concentrations: high (when the quenching is mainly static) and low (when the quenching is accelerated by motion).     

On the influence of coloration on the intrinsic luminescence in NaCl

The dependence of quenching of the π and σ intrinsic luminescence in pure and doped NaCl crystals has been studied as a function of irradiation time near LNT. Three stages in the luminescence quenching have been found. The first stage is very dependent on impurities concentration and is inhibited for high concentration.     

Effect of vapors of water and organic solvents on the luminescence of cation-exchange membranes immobilized with cyclometalated Pt(II) complexes

The luminescence quenching of cation-exchange membranes immobilized with cyclometalated Pt(II) complexes by vapors of water and some organic solvents (methanol, ethanol, isopropanol, n-butanol, acetonitrile, and acetone) is studied. The mechanism of the luminescence quenching of complexes is discussed.     

Dynamic fluorescence quenching and the highest excited states of molecules

The dynamic fluorescence quenching in organic molecules, or quenching of the second kind according to Vavilov’s classification, is an efficient method of investigating excited states in solutions and is widely used in various fields. The effect of quenching on the intensity of the fluorescence from the first and higher singlet states of organic molecules is studied. The results may serve as a basis for determining the nature of the short-wavelength luminescence and can be used to distinguish the S _n fluorescence from the comparably intense luminescence of impurities, which is a very important problem when investigating such emissions. A method for obtaining dynamic quenching by specially chosen quenchers is proposed. The method is based on an experimentally found strong increase in the constants of bimolecular collisions of luminophore and quencher molecules when the luminophore is excited through the highest singlet states.     

Spectral-luminescence study of the formation of QD-sulfophthalocyanine molecule complexes in an aqueous solution

The spectral-luminescence manifestations of the formation of quantum dot (QD)-phthalocyanine complexes as a result of electrostatic interaction have been investigated. Effective QD luminescence quenching has been found in complexes of this type. The luminescence of the molecules associated in complexes with QDs is also partially quenched. A mathematical model of the formation of QD-organic molecule complexes is proposed.     

Temperature dependence of the photoluminescence of CdTe/ZnTe quantum-dot superlattices

The temperature dependence of the luminescence of CdTe/ZnTe quantum-dot superlattices (self-assembled quantum-dot multilayers) with ZnTe spacers of various thicknesses was studied. Luminescence quenching observed to occur with increasing temperature is shown to depend substantially on the thickness of the ZnTe spacer. Particular attention is focused on the temperature dependence of the luminescence of a structure with the smallest ZnTe layer thickness, containing clusters of regularly arranged quantum dots. The luminescence line of tunneling-coupled quantum dots appearing in this structure exhibits an unusual temperature dependence, more specifically, an anomalously large shift of the peak position and fast luminescence quenching with increasing temperature.     

Properties of erbium luminescence in bulk crystals of silicon carbide

The infrared luminescence of Er³⁺ ions has been studied in bulk crystals of silicon carbide 6H-SiC doped with erbium in the process of their growth. The erbium centers of different symmetry in the crystals are revealed by the EPR technique. A number of intense luminescence bands of erbium ions are observed at a wavelength of about 1.54 μm. The luminescence can be excited by the light with quantum energies above and below the band gap of SiC. It is found that the luminescence exhibits unusual temperature behavior: as the temperature increases, the luminescence intensity abruptly rises starting with 77 K, passes through a maximum at ∼240 K, and, in the vicinity of ∼400 K, decreases down to the values observed at 77 K. The activation energies for the flare-up and quenching of the Er³⁺ luminescence are estimated at E _A ≈130 and ≈350 meV, respectively. The mechanisms of the flare-up and quenching of the Er³⁺ luminescence in SiC are discussed. __________ Translated from Fizika Tverdogo Tela, Vol. 42, No. 5, 2000, pp. 809–815. Original Russian Text Copyright ? 2000 by Babunts, Vetrov, Il’in, Mokhov, Romanov, Khramtsov, Baranov.     

Coherent detection of THz waves based on THz-induced time-resolved luminescence quenching in bulk gallium arsenide

A kind of photoluminescence quenching, in which the time-resolved photoluminescence is modulated by a THz pulse, has been theoretically investigated by performing the ensemble Monte Carlo method in bulk gallium arsenide (GaAs) at room temperature. The quenching ratio could reach up to 50% under a strong THz field (100 kV/cm). The range in which luminescence quenching is linearly proportional to the THz field could be over 60 kV/cm. On the basis of these results, a principle for THz modulation and coherent detection is proposed.     

Optical measurements of the probability of atom de-excitation on the surface of transparent windows in ultrashort cells

A method for measuring the probability of excitation quenching of atoms on the surface of transparent dielectrics using data on the dependence of the luminescence intensity of atom in an ultrashort cell on the distance between its windows is suggested. Two possibilities of performing the measurements based on the luminescence recording are considered: from the volume at the atomic transition frequency and from the near-wall region in the range of distant wings of atomic lines.     

External heavy atom effect on the emission of carbazole

External heavy atom induced quenching of luminescence emission of carbazole in n-hexane and methylcyclohexane in the presence of chloro- and bromoacetic acids at 300 K and 77 K is described. A straight line relation between fluorescence quenching rate constant and the acid dissociation constant of chloroacetic acids, which is related to electron affinity, is observed. Different photophysical parameters at 77 K of unperturbed and perturbed fluorescent carbazole in ternary solutions have been determined and suitable reaction mechanism for quenching has been proposed. Inference has been drawn about complex formation in the triplet state of carbazole from the biexponential nature of the phosphorescence decay curve.     

Quantum yields of selective and non-selective luminescence in solid solutions

The quantum yields of selective and non-selective luminescence have been calculated in terms of the Markoffian and non-Markoffian theories of jumping quenching. The activator concentration dependences are shown to be functionally different in a range where the yields are readily measurable and thus applicable for discrimination between the two theories. The concentration dependence of radiation anisotropy has been calculated under conditions in which luminescence depolarization is accompanied by luminescence quenching either by alien admixtures or activator dimers.     

Effect of C-H bonds on the quenching of luminescent lanthanide chelates

The quenching of europium(III) and terbium(III) chelate luminescence by high-energy C-H vibrational manifolds was studied with two types of stable chelates, i.e., a seven-dentate phenylethynylpyridine derivative and a nine-dentate terpyridine derivative. The replacement of C-H bonds by C-D bonds in the chelating parts of the ligands had a clear positive effect on Eu³⁺ luminescence but a negligible effect on Tb²⁺ luminescence. In aqueous solution, however, the positive effect was undetectable, if the chelating ligand did not create complete shielding of the ion against aqueous quenching. In chelates, where the coordination of water molecules to the inner sphere is prevented, the residual quenching through C-H vibrational quanta can be avoided by replacement of all C-H bonds in the vicinity of the emitting ion by C-D bonds.     

Effect of copper on dislocation luminescence centers in silicon

The effect of copper on dislocation luminescence centers in silicon has been investigated using photoluminescence and transmission electron microscopy. It has been demonstrated that there exist two main mechanisms responsible for quenching of dislocation luminescence by the copper impurity. The first mechanism is dominant at high copper concentrations and associated with the decrease in the time of nonradiative recombination of nonequilibrium charge carriers due to the formation of copper precipitates in silicon. This leads to the quenching of the entire dislocation luminescence and the edge exciton luminescence. The second mechanism is associated with the interaction of individual copper atoms with deep dislocation centers D1/D2, which results in the passivation of the recombination activity of these centers. This mechanism takes place even at room temperature and is highly effective at low copper concentrations.     

Quenching of photoluminescence from GaAs/AlGaAs single quantum well by an electric field at high temperature

Photoluminescence measurements at room temperature and at liquid nitrogen temperature on a GaAs/AlGaAs single quantum well structure subject to an electric field are performed to study (i) the photoluminescence quenching and (ii) the shift in the photoluminescence energy induced by the field. The observed shifts in the luminescence energies are explained successfully in terms of the field induced electron-hole separation model. For the quenching of the luminescence intensities, more work, particularly on nonradiative processes, is required to clarify the mechanism.