Luminescence of molecular silver clusters in oxyfluoride glasses

Luminescence spectra of silver-containing oxyfluoride glasses have been investigated in the excitation spectral range of 360–480 nm. Analysis of the luminescence spectra shows that silver in oxyfluoride glasses that contain no strong reducers and were subjected to heat treatment affecting redox processes exists in the form of neutral atoms and neutral molecular Ag₂, Ag₃, and Ag₄ clusters.     

Photoinduced electron transfer involving radical ions in multicomponent solutions

A phenomenological study of a specific radical ion mechanism of formation of metastable products is presented. Energy level diagrams of fullerene C₆₀, tetramethylbenzidine, perylene, and radical ion pairs in toluene and benzonitrile are constructed. The possibility for obtaining fast optical switching and limiting in solutions of C₆₀ fullerene, tetramethylbenzidine, and perylene in toluene is analyzed.     

The use of a photoinduced electron-transfer reaction for optical limiting in fullerene-containing solutions

Optical limiting was experimentally studied in C₆₀ fullerene-based multicomponent solutions that are characterized by photoinduced electron-transfer processes with the formation of ion-radical pairs. The limitation efficiency in these solutions increased as a result of enhancement of absorption in the molecular system in an excited state. It was found that the spectral and time capabilities of limiters based on fullerene-containing media can be extended with the use of radical ions.Translated from Khimiya Vysokikh Energii, Vol. 39, No. 1, 2005, pp. 32–35.Original Russian Text Copyright © 2005 by Gryaznova, Danilov, Khrebtov, Shakhverdov.     

Efficiency of the use of two-photon absorption in impurity liquid crystals as a mechanism of optical limitation

An analysis is made of the advantages of impurity liquid-crystal systems that are associated with the existence of the excitonic mechanism of electronic excitation energy transfer in them. Using the two-photon absorption in such systems, one can substantially expand the dynamic range of optical limitation.     

A cross-relaxation mechanism of fluorescence quenching in complexes of lanthanide ions with organic ligands

For the first time, direct experimental evidence of a new mechanism for the quenching of fluorescence of organic ligands (L) in complex compounds with lanthanide ions (Ln³⁺) is obtained. By analogy with the mechanism of luminescence quenching upon pair interactions of Ln³⁺ ions in inorganic systems, this mechanism is called the cross-relaxation mechanism. The experiments are performed with complexes of Tb³⁺ with dianions of halogen-substituted fluoresceins (HSFs): 4,5-dibromo-and 4,5-diiodofluorescein, eosin B, eosin, erythrosin, and Rose Bengal in dimethyl sulfoxide. In accordance with this mechanism—exchange energy transfer, L^2?(*S ₁), Tb³⁺(⁷ F ₆)→L^2?(T ₁), Tb³⁺(⁷ F _{5, 4}), allowed by the spin selection rules—an increase in the quantum yield of formation of the triplet state (Φ_T) of a ligand L^2? and a decrease in the quantum yield of fluorescence (Φ_fl) are found to take place upon complexation. The efficiency of this process amounts to ～1 in accordance with the equality Φ_fl+Φ_T=1, valid for solutions of HSFs. The possibility of other processes leading to a similar effect, specifically, recharging of the system (as for complexes of HSFs with Eu³⁺ and ³⁺) is considered. An example of inductive resonance interactions in complexes of HSFs with Pr³⁺ is given. The manifestation of equilibrium between outer-sphere and inner-sphere complexes in the photophysics of complexes of metals with HSFs is discussed.

     

Absorption and fluorescence of complexes of compounds of anthracene carboxylic acids with metal ions in liquid solutions

We have studied the absorption and fluorescent properties of complexes formed by compounds of anthracene-9-carboxylic acid with metal cations in dimethyl sulfoxide and ethanol. The composition and stability of these complexes has been determined. It is shown that when lanthanide ions are added (Ln³⁺) 21 complexes are formed predominantly, i.e., RCOO^– Ln^{3+ –}OOCR, while with Cd²⁺ the complexes are mainly 11, i.e., RCOO^– Cd²⁺. We have considered the principal mechanisms for the deactivation of excitation in complexes based on the RE ions (dipole-dipole energy transfer and electron transfer). The interactions were shown to be inner-sphere in character in the ion triplets, and outer-sphere in the ion pairs. The metal-ligand distance in the 21 complexes is estimated to be 0.5–0.6 nm.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 6, pp. 673–682, November–December, 1989.In conclusion the authors wish to thank A. S. Cherkasov for synthesizing and making available the ACA and for discussing the results of the investigation.     

Specific features of thermal dissolution of silver and gold thin films in silicate glass

It has been shown experimentally that the thermal dissolution of silver and gold thin films in silicate glass is accompanied by the formation of a monolayer of silver and gold micro- and nanocrystals, respectively, on the surface of the glass. These processes occur at temperatures well below the melting temperature of the metal. Microcrystals are formed predominantly at the edges of islands of the metal film, where there is a sufficient amount of the material for their growth. Silver and gold nanocrystals are formed in the case when atoms of the metal dissolved in the glass repeatedly emerge on the glass surface. Silver and gold dissolved in the glass exist not only in the form of atoms and ions but also in the form of charged and neutral molecular clusters.

     

Luminescence of dipicolinic complexes of lanthanide ions

The luminescence decay times τ_lum of the complexes of the ions Tb(III), Eu(III), Sm(III), Dy(III), and Yb(III) with dipicolinic acid (DPA) dissolved in protonated and deuterated water, methanol, and dimethyl sulfoxide are measured. The values of τ_lum for crystals H₃[Ln(DPA)₃]·nH₂O and their aqueous solutions coincide, which points to the identity of the environment in the nearest spheres of an ion in both cases. A comparison of τ_lum of solutions of the complexes in H₂O and D₂O, as well as in CH₃OH, CH₃OD, CD₃OD, DMSO-h ₆, and DMSO-d ₆ shows that the molecular groups in the second and third spheres of an ion, exhibiting high-frequency vibrations, have a noticeable effect on the rate constants of nonradiative transitions k _nr in the ion. From this comparison, some inferences on the structure of the solvate shell of the Ln(DPA) ₃ ^3? complexes in the solvents used are made. The contributions to k _nr of Eu(III), Tb(III), Sm(III), Dy(III), Nd(III), and Yb(III) made by OH and CH groups located at different distances from the ion are estimated. It is demonstrated that the dependence of k _nr on the distance to the OH and CH groups is steeper for the Eu(III) and Tb(III) ions than for the remaining ions.