L. Krajczyk

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.

Influence of oxidation–reduction treatment on the microstructure of Co/SiO2 catalyst

Abstract Evolution of microstructure and morphology of Co particles in a Co/SiO 2 catalyst during oxidation–reduction treatment was studied by electron microscopy methods. Attention was paid to phenomena taking place on the surface of particles. The redispersion of Co particles and surface roughening were observed. Catalytic activity was tested by benzene hydrogenation.

Effect of high-temperature reduction on Co/SiO2 catalysts activity in the hydrogenation of benzene

The influence of the high reduction temperature on the activity of Co/SiO2 catalysts in benzene hydrogenation has been studied. The decrease of activity is caused by strong metal-support interaction.

Microstructure and silver nanoparticles in ion-exchanged and deformed soda-lime silicate glasses

Abstract Optical absorption, microspectrophotometry, thermally stimulated depolarization current, and transmission electron microscopy were applied to a commercial multicomponent soda-lime silicate glass subjected to the Na + ⇔Ag + ion-exchange, annealing in air or hydrogen, and to mechanical stretching. The treatments affect both the matrix microstructure and the morphology of the silver particles. Mechanical stretching of the exchanged specimens annealed in hydrogen induces the most interesting effects. Secondary phase separation occurs within the glassy matrix, and causes drastic changes of the thermocurrent data, which are interpreted in terms of the Maxwell–Wagner interfacial polarization. Elongation of the spherical silver nanoparticles produces a remarkable dichroism of the optical absorption, which could be exploited for new applications. The sample stretching affects only particles with a diameter larger than 5 nm interpreted as a threshold size, at least at the stresses used in the present work.

Some effects of γ-irradiation in soda-lime silicate glasses

Abstract Nanosized metallic silver particles have been formed in multicomponent commercial soda-lime silicate glasses partly substituted with ionic silver and irradiated at room temperature by γ-rays from a 60Co-source (1.33 MeV). To characterize the obtained composites, combined measurements of thermally stimulated depolarization current and optical absorption, accompanied by microspectrophotometric analysis and electron microscopy observations have been used. It has been shown that γ-irradiation might be an effective means to modify and control the concentration, size and spatial distribution of the dopant within the near-surface layer of the glass-matrix. This procedure also allows the conversion of some glassy areas in this region into a partially crystalline material with improved mechanical characteristics.

FORMATION OF SILVER COLLOIDS ON ION EXCHANGED SODA LIME SILICATE GLASSES BY IRRADIATION

Abstract The effect of ionizing radiation (gamma rays, X-rays and electrons) on soda lime silicate glasses, in which part of the Na+ was substituted by Ag+ by means of an ionic exchange process, was studied. The techniques of thermally stimulated depolarization current (TSDC) and transmission electron microscopy (TEM) were employed to follow the formation of silver colloids by irradiation. Also the thermoluminescence (TL) of the samples was measured and three peaks between room temperature and 450°C were observed. The TEM and TSDC results agree that, as expected, ionizing radiation promotes the formation of silver colloids on the ion exchanged surface of soda lime glasses. Soft X-rays are much more efficient in the process than gamma rays and electrons. The correlation with thermoluminescence glow curves indicates that the intensity of a TL peak at 230°C can provide a rapid means of evaluating the presence of silver colloids. TL sensitivities, measured as area under the glow curve per unit mass and unit dose, are very similar for ion exchanged and not exchanged samples submitted to X-ray irradiation, although the peak temperatures differ in about 40°C in the two cases. For both electron and gamma irradiated samples, the TL sensitivity drops about an order of magnitude when compared to the X-ray irradiated ones.

Preparation and optical properties of soda-lime silicate glasses partially substituted by copper

The ion-exchange process was used to introduce copper ions into soda lime silicate glasses (SLS), the composition of which corresponds to the miscibility gape in the Na 2 O-SiO 2 system. The samples have been immersed either in a molten Cu 2 Cl 2 or CuCl 2 at various temperatures from the range 720-940 v K for different time. The observed green colour of glass is related with the 790-nm absorption band related to the cupric ions. The annealing either in air or in the hydrogen atmosphere was used for the reduction of copper. The effectiveness of these procedures was analysed on a basis of the penetration profiles monitored by roentgenographic methods (diffraction and EDAX). Transmission electron microscopy (TEM) observations of the replicated surface and common optical absorption measurements have been used to study the morphology of the dopant ions.

Sodium motion in phase-separated and silver-exchanged soda-lime silicate glasses

Abstract Thermally stimulated depolarization currents, absorption microspectrophotometry and electron microscopy were used to characterize soda-lime silicate glasses with droplets of the Na2O-rich phase distributed within the SiO2-rich matrix and with nanosized particles of elemental silver. It has been shown that the detected polarizations are mainly of interfacial type related with different modes of the Na+ motion affected by the dopant as well as thermal and mechanical treatments of samples.

Structural changes of soda-lime silica glass induced by a two-step ion exchange

Introduction of silver or copper ions in soda-lime silica glass has been investigated by studying the data obtained from optical absorption measurements and the transmission electron microscopy performances. It has been stated that the optical and structural characteristics of the doped specimens are effectively controlled by the dopant concentrations and parameters of both, the ion-exchange procedures and the annealing treatments applied afterwards. By sequential ion exchange of as received specimens in molten baths of Cu2Cl2 and (AgNO3 in NaNO3), the composition and electronic structure of the elemental-nanoclusters have been altered. Moreover, depending on the order of annealing, different microstructures were created in the fabricated composites. Like this, the two-step exchange determines a new engineering way new materials with desired optical properties could be produced.