Controlling Growth of Poly (Triethylene Glycol Acrylate-Co-Spiropyran Acrylate) Copolymer Liquid Films on a Hydrophilic Surface by Light and Temperature

A quartz crystal microbalance with dissipation monitoring (QCM-D) was employed for in situ investigations of the effect of temperature and light on the conformational changes of a poly (triethylene glycol acrylate-co-spiropyran acrylate) (P (TEGA-co-SPA)) copolymer containing 12–14% of spiropyran at the silica–water interface. By monitoring shifts in resonance frequency and in acoustic dissipation as a function of temperature and illumination conditions, we investigated the evolution of viscoelastic properties of the P (TEGA-co-SPA)-rich wetting layer growing on the sensor, from which we deduced the characteristic coil-to-globule transition temperature, corresponding to the lower critical solution temperature (LCST) of the PTEGA part. We show that the coil-to-globule transition of the adsorbed copolymer being exposed to visible or UV light shifts to lower LCST as compared to the bulk solution: the transition temperature determined acoustically on the surface is 4 to 8 K lower than the cloud point temperature reported by UV/VIS spectroscopy in aqueous solution. We attribute our findings to non-equilibrium effects caused by confinement of the copolymer chains on the surface. Thermal stimuli and light can be used to manipulate the film formation process and the film’s conformational state, which affects its subsequent response behavior

Influence of process parameters on the incorporation of phosphorus into silica soot material during MCVD process

The incorporation of phosphorus into silica soot material strongly changes during the multistep preparation process of the MCVD technology in combination with solution doping for Al and rare earths. We report on the influence of various process parameters on the phosphorus concentration, the bond types of phosphorus atoms and the relative density of the soot material. By optimization of the process the phosphorus concentration of the presintered soot could be increased by around 10% in comparison to the conventional treatment. The understanding of the interdependencies allows an improvement of the preparation process of phosphorus co-doped RE doped silica laser fibers with MCVD technology

Diffusion and interface effects during preparation of all-solid microstructured fibers

All-solid microstructured optical fibers (MOF) allow the realization of very flexible optical waveguide designs. They are prepared by stacking of doped silica rods or canes in complex arrangements. Typical dopants in silica matrices are germanium and phosphorus to increase the refractive index (RI), or boron and fluorine to decrease the RI. However, the direct interface contact of stacking elements often causes interrelated chemical reactions or evaporation during thermal processing. The obtained fiber structures after the final drawing step thus tend to deviate from the targeted structure risking degrading their favored optical functionality. Dopant profiles and design parameters(e.g., the RI homogeneity of the cladding) are controlled by the combination of diffusion and equilibrium conditions of evaporation reactions. We show simulation results of diffusion and thermal dissociation in germanium and fluorine doped silica rod arrangements according to the monitored geometrical disturbances in stretched canes or drawn fibers. The paper indicates geometrical limits of dopant structures in sub-μm-level depending on the dopant concentration and the thermal conditions during the drawing process. The presented results thus enable an optimized planning of the preform parameters avoiding unwanted alterations in dopant concentration profiles or in design parameters encountered during the drawing process

Correlation between ionic mobility and plastic flow events in NaPo3-NaCl-Na2SO4 glasses

We report on the evolution of the mechanical and electrical properties of sodium metaphosphate glasses with addition of sodium sulfate or sodium chloride. The addition of these two sodium salts converts the medium-range order of our glasses from 2D phosphate chains to a mixed 1D + 2D network similar to ionic glasses, while the short-range order of the phosphate units remains unaffected. Replacing the phosphate units by chloride ion monotonically decreases the glass transition temperature, but enhances the Young's modulus and moderately increases the ionic conductivity. On the other hand, the sulfate group decreases the glass transition temperature as well, though the Young's modulus remains constant, while the ionic conductivity strongly increases. The changes in conductivity are related to the enhancement of the ionic mobility in these glasses, which in turn affect the size and distribution of the plastic events taking place during indentation-driven deformation.Bruno Poletto Rodrigues, Rene Limbach, Gabriel Buzatto de Souza, Heike Ebendorff-Heidepriem and Lothar Wondracze

Impact of rare earth doping on the luminescence of lanthanum aluminum silicate glasses for radiation sensing

Large core soft glass fibers have been demonstrated to be promising candidates as intrinsic fiber sensors for radiation detection and dosimetry applications. Doping with rare earth ions enhanced their radiation sensitivity. SiO2-Al2O3-La2O3 (SAL) glasses offer easy fabrication of large core fibers with high rare earth concentration and higher mechanical strength than soft glasses. This paper evaluates the suitability of the SAL glass type for radiation dosimetry based on optically stimulated luminescence (OSL) via a comprehensive investigation of the spectroscopic and dosimetric properties of undoped and differently rare earth doped bulk SAL glass samples. Due to the low intensity of the rare earth luminescence peaks in the 250–400 nm OSL detection range, the OSL response for all the SAL glasses is not caused by the rare earth ions but by radiation-induced defects that act as intrinsic centers for the recombination of electrons and holes produced by the ionizing radiation, trapped in fabrication induced defect centers, and then released via stimulation with 470 nm light. The rare earth ions interfere with these processes involving intrinsic centers. This dosimetric behavior of highly rare earth doped SAL glasses suggests that enhancement of OSL response requires lower rare earth concentrations and/or longer wavelength OSL detection range.Ruth E. Shaw, Christopher A. G. Kalnins, Carly A. Whittaker, Jillian E. Moffatt, Georgios Tsiminis, Elizaveta Klantsataya, David Ottaway, Nigel A. Spooner, Doris Litzkendorf, Anne Matthes, Anka Schwuchow, Katrin Wondraczek, and Heike Ebendorff-Heideprie

Decoupling mobility and charge carrier concentration in AgR-AgPO3 glasses (R=Cl, Br, I)

Halide-containing silver phosphate glasses have been used as model systems for the study of the ionic conductivity of oxide glasses for the past 50 years, mostly due to the massive increase in conductivity observed as the halide concentration is increased, even if the molar ratio of silver is kept constant. Furthermore there is still no consensus if the increased conductivity is due to an enhancement of the number of effective charge carriers (glass as a weak electrolyte) or a higher charge carrier mobility (glass as a strong electrolyte). In this work we investigate the electrical properties of silver-halide-containing silver metaphosphate glasses through Impedance Spectroscopy. We find the glasses to follow the “canonical scaling”, which coupled with the diffusional nature of the conductivity allows us to show that the number of effective charge carriers remains constant with increasing halide concentration, and that the conductivity follows the same scaling as the ionic mobility.Bruno P. Rodrigues, Heike Ebendorff-Heidepriem, Lothar Wondracze

Magnetic and magneto-optical quenching in (Mn[2+], Sr[2+]) metaphosphate glasses

Transition metal ions such as Mn[2+], Fe[2+], or Co[2+] provide an interesting alternative to rare earth dopants in optically active glasses. In terms of their magneto-optical properties, they are not yet very well exploited. Here, we report on the effect of Mn[2+] on Faraday rotation in a metaphosphate glass matrix along the join Mn{x}Sr{1-x}(PO{3}){2} with x = 0...1. Mn[2+] shows small optical extinction in the visible spectral range and, compared to other transition metal ions, a high effective magnetic moment. At high Mn- levels, however, the magneto-optical activity of Mn[2+] is strongly quenched due to ionic clustering. The magnetic properties of the heavily Mn[2+]-loaded phosphate matrix are dominated by a superexchange interaction in the Mn[2+]-O-Mn[2+] bridge with antiparallel spin alignment between Mn[2+] and O[2-] species. The apparent paramagnetic potential of Mn[2+] species can therefore not be exploited at room temperature

Broadband NIR photoluminescence from Bi-doped Ba2P2O7 crystals: Insights into the nature of NIR-emitting Bismuth centers

We report on a novel type of Bi-doped crystal that exhibits ultrabroadband photoluminescence in the near infrared (NIR). Emission centers can be generated and degenerated reversibly by annealing the material in CO atmosphere and air, respectively, indicating that emission is related to the presence of Bi-species in low valence states. Correlating static and dynamic excitation and emission data with the size and charge of available lattice sites suggests that two types of Bi-0-species, each located on one of the two available Ba2+ lattice sites, are responsible for NIR photoemission. This is further confirmed by the absence of NIR emission in polycrystalline Ca2P2O7:Bi and Sr2P2O7:Bi. Excitation is assigned to transitions between the doubly degenerated ground state S-4(3/2) and the degenerated excited levels D-2(3/2), D-2(5/2) and P-2(1/2), respectively. NIR emission is attributed to D-2(3/2) -> S-4(3/2). The NIR emission center can coexist with Bi2+ species. Then, also Bi2+ is accommodated on one of the two Ba2+-sites. Energy transfer between Bi2+ ions occurs within a critical distance of 25.9 angstrom. (C) 2010 Optical Society of Americ

Complex Faraday Rotation in Microstructured Magneto-optical Fiber Waveguides

Magneto-optical glasses are of considerable current interest, primarily for applications in fiber circuitry, optical isolation, all-optical diodes, optical switching and modulation. While the benchmark materials are still crystalline, glasses offer a variety of unique advantages, such as very high rare-earth and heavy-metal solubility and, in principle, the possibility of being produced in fiber form. In comparison to conventional fiber-drawing processes, pressure-assisted melt-filling of microcapillaries or photonic crystal fibers with magneto-optical glasses offers an alternative route to creating complex waveguide architectures from unusual combinations of glasses. For instance, strongly diamagnetic tellurite or chalcogenide glasses with high refractive index can be combined with silica in an all-solid, microstructured waveguide. This promises the implementation of as-yet-unsuitable but strongly active glass candidates as fiber waveguides, for example in photonic crystal fibers