K. Maruszewski

Optical properties of Eu(III) chelates trapped in silica gel glasses

Abstract Preparation and optical properties of silica gel glasses doped with Eu(III) chelates (the complexes of β-diketones) are described. In particular the emission and excitation spectra of the precursor salts and glasses are reported. The assignment of electronic levels was proposed and the intensity analysis of the f–f transitions was performed. The decay times of 5D0 levels of Eu(III) complexes in gels are analyzed and compared with those reported for precursor salts.

Nature and optical behaviour of heavily europium-doped silica glasses obtained by the sol–gel method

Abstract Silica glasses doped with Eu 3+ were prepared by the sol–gel method. The effects of the synthetic procedure on optical properties of the europium heavily doped glasses have been investigated. The fluorescence characteristics of Eu 3+ have been measured for several thermal stages of the sol–gel process. In particular, we have studied aggregation of the Eu ions leading to creation of nanocrystallites during the thermal treatment of silica glasses. The size of the nanocrystalites and their structure have been determined by means of high-resolution transmission electron microscopy and X-ray diffraction. The influence of the OH − groups on the luminescence lifetimes of Eu 3+ has been studied. A broad luminescence band in the blue region has been observed for the silica glasses possessing silanol (Si–OH) groups. Its intensity decreases with the increasing temperature of sintering for the samples treated in the presence of NH 4 Cl. In the case of those heated at high temperatures, doubly doped with Eu and Al silica glasses, a blue emission assigned to the Eu 2+ ions has been observed. Its intensity increases with the Al 3+ ions concentration.

Physicochemical properties of Ru(bpy)32+ entrapped in silicate bulks and fiber thin films prepared by the sol–gel method

Abstract Silicate porous xerogels doped with ruthenium bipyridine (Ru(bpy) 3 2+ ) complex have been obtained in the bulk form and in thin films on optical fibers. The hypsochromic shifts in the absorption and emission maxima are accompanied by fourfold increase in the lifetimes of the entrapped complex. The temperature-dependent lifetimes reveal that silicate xerogels induce two competing thermally activated processes in the excited state decay of the immobilized complex. The excited state lifetimes of the doped bulk xerogels and the fibers coated with thin films containing Ru(bpy) 3 2+ are virtually identical to those obtained for the fibers coated with additional gas-impermeable layers.

Fluorescence and Absorption Probe of Metal Ion Centers in Silicates Obtained by the Sol-Gel Technique

An optical probe of the structure of metal ion centers in sol-gel systems based on Eu3+ and Nd3+ emission and absorption measurements has been developed. The effects of the structure and composition of organic complexes of Eu3+ on the clustering processes and retention of water molecules in the gel and glasses were investigated. Mechanical properties of systems prepared with Triton detergent were also investigated. The studies have been performed for two types of complexes of lanthanides, with β-diketones as the precursor lanthanide salts. The emission, excitation and absorption spectra of the precursor salts, gels and glasses heated to 1100 K were measured. Splitting of the levels and electronic transition probabilities were analyzed. The IR spectra were used for the detection of the OH− modes in the glasses.

Ballistic aggregation: an alternative approach to modeling of silica sol–gel structures

Abstract An algorithm based on ballistic aggregation is discussed as an alternative to the commonly used, much slower diffusion-based algorithms for modeling of atomic structure of silica gels. The algorithm is shown to be capable of producing a wide range of structures: from extremely porous to compact (dense) ones. The importance of capture distance as a controlling parameter is discussed. Electron microscope images of actual silica gels morphologically very similar to the rendered images of the simulated aggregates are shown.

Optical properties of Pr3+ doped silica gel glasses obtained by sol–gel method

Abstract Thermally densified silica glasses doped with Pr3+ ions were prepared by sol–gel method. Three procedures of synthesis are described. Absorption, emission and excitation spectra of Pr3+ doped silica glasses obtained by sol–gel method are reported. We found on the basis of now presented results and those earlier reported that intensities of the absorption bands of Pr3+ change with concentration nonlinearly, especially in the range of 3H4→3P2; 3P0 and 1D2 transitions. This phenomenon could be caused by clustering, which leads to cooperative interactions. On the basis of the absorption spectra measurement, the energy level diagram was prepared which helps in the explanation of the emission properties of glasses synthesized by different techniques. The luminescence spectra were dependent on excitation wavelength. The spectra excited in high UV range exhibited, except emission in the red range corresponding to the 1D2→3H4 transition, a broad band emission with characteristic holes at the envelope corresponding to the 3P2, (3P1, 1I6) and 3P0 terms. Nature of this broad band emission is discussed. The observed holes result from reabsorption processes, which are controlled by concentration of active ions. Mechanism of their occurrence remains unknown. No emission from 3P0 level was observed for some kind of glasses, for another one the emission from 1D2 and 3P0 levels was detected.

Electroreduction of methyl viologen in methanol and silicate thin films prepared by the sol–gel method

Abstract Bulk methanol solutions of methyl viologen (paraquat) can be reversibly reduced to its blue cation radical on transparent ITO electrodes. The intensity of the coloration is directly proportional to voltage applied to the cell. Such effect does not occur for aqueous paraquat solutions. Reversible blue coloration can also be obtained for a MV2+-doped silicate thin film obtained by the sol-technique and sandwiched between two ITO plates.

Spectroscopic properties of erbium doped silica glasses obtained by sol-gel method

Abstract The spectroscopic properties of erbium doped silica glasses obtained by sol-gel technology have been investigated. The emission properties of Er3+ ion are discussed on a basis of the absorption and emission spectra. The transmission and emission characteristics of Er doped silica fibers are presented. The efficient emission in the mid-ir region (at 1.55 μm) was observed. It has been found that, for the high concentration (1000 ppm) Er doped fiber, the 1.55 μm emission was completely quenched. Instead of this emission, the efficient green anti-Stokes emission (after laser diode pumping at 980 nm) was observed.

Spectroscopic and physicochemical properties of rare-earth phthalocyanines entrapped in sol-gel glasses

Abstract The electronic absorption spectra of samarium and neodymium phthalocyanines in DMSO and entrapped in glasses obtained via the sol-gel technique have been obtained. Decrease in concentration of metallophtalocyanines in DMSO leads to observed changes in the relative intensifies of the two bands in the Q-band region. This behavior could be explained by the shifts in equilibrium between the LnPc 2 and LnPc + forms, caused by the dilution. In view of this interpretation, the entrapment of the metallophthalocyanines in the sol-gel glass matrices shifts the diphthalocyanine ⇆ monophthalocyanine equilibrium towards the monophthalocyanine (LnPc + ) form.

Raman Spectra of Molecules Adsorbed on Ag Centers in Sol-Gel Matrices

Silica monoliths and submicron spheres containing silver nanoparticles have been obtained using the sol gel technology. The Ag inclusions were synthesized via the counterdiffusion method. The silver-doped matrices were immersed in solutions of an organic dye (indocyanine green) enabling the solute molecules to interact with surface of the Ag-doped silica matrices. Raman spectra of free solutions of the organic molecules under investigation, the impregnated Ag-doped matrices and the impregnated Ag-free matrices have been measured. The impregnated silica matrices which did not contain silver nanoparticles were used as a reference. These experiments have been performed in order to establish if Raman signal enhancement could be obtained by adsorption of organic molecules on the surface of Ag inclusions in the sol-gel matrices analogously to the standard surface-enhanced Raman spectroscopy (SERS) method.