PHOTO CHROMATIC SENSORS OF MULTINARY MIXED VALENCE INORGANIC MICRO NEEDLES

The recent I-U measurements on the individual micro needle-shaped crystals, of the ternary mixed valence compound In5Se5Cl, crystallizing in the monoclinic crystal system (P21/m), showed significant light sensitivities. Micro needles of In5Se5Cl “glued” on Si- and Cu- substrates were measured under five different wavelengths with various irradiation intensities to investigate their photo chromatic sensing behavior along with the substrate’s influence. In the measuring voltage range 0 – 3 V and maximal LED illumination intensity, current jumps above two orders of magnitude were observed for white light (4100 K; 200 lm), followed by the blue light (460 nm; 976 mW). The amber light (590 nm; 203 mW) exhibited the lowest response. Green- and blue light were selected to determine the substrate’s effect. The micro-needles chips prepared with Si-substrates displayed higher currents for the same voltages in comparison to those prepared with Cusubstrates. These differences decreased with the voltage increase for both employed wavelengths. The mutual structural substitution of a selenium with sulfur, led to the compound In5Se4Cl. The later crystallizes similarly to In5Se5Cl. Its I-U measurements recorded with green and blue light, on Cu-substrate chips within the voltage range 0 -3 V, revealed more pronounced photo chromatic sensorial for both wavelengths used. These differences increased with the voltage increase for both employed wavelengths. At 3 V, current increases up to 2.2 times and 2.4 times were observed for the green light and blue light respectively. Typically high and better distinguishable sensorial activity was observed for all the employed wavelengths using chips with In5Se4Cl crystals on Cu-substrate, even at minimal irradiation LED power (0.25 %). The micro-reflection measurements of both needle-shaped crystals displayed a substitution dependent band-gap. For In5Se5Cl the band gap was estimated at 580 nm. Thickness interference oscillations strongly damped due to structural inhomogeneity or defect-related absorption suggest two possible band gaps for In5Se4Cl; at 540 nm or at 620 nm

Synthesis and Features of Luminescent Bromo- and Iodohectorite Nanoclay Materials

The smectites represent a versatile class of clay minerals with broad usage in industrial applications, e.g., cosmetics, drug delivery, bioimaging, etc. Synthetic hectorite Na-0.7(Mg5.5Li0.3)[Si8O20](OH)(4) is a distinct material from this class due to its low-cost production method that allows to design its structure to match better the applications. In the current work, we have synthesized for the first time ever nanoclay materials based on the hectorite structure but with the hydroxyl groups (OH-) replaced by Br- or I-, yielding bromohectorite (Br-Hec) and iodohectorite (I-Hec). It was aimed that these materials would be used as phosphors. Thus, OH- replacement was done to avoid luminescence quenching by multiphonon de-excitation. The crystal structure is similar to nanocrystalline fluorohectorite, having the d(001) spacing of 14.30 angstrom and 3 nm crystallite size along the 00l direction. The synthetic materials studied here show strong potential to act as host lattices for optically active species, possessing mesoporous structure with high specific surface area (385 and 363 m(2) g(-1) for Br-Hec and I-Hec, respectively) and good thermal stability up to 800 degrees C. Both materials also present strong blue-green emission under UV radiation and short persistent luminescence (ca. 5 s). The luminescence features are attributed to Ti3+/Ti-IV impurities acting as the emitting center in these materials

Effect of alkoxy-spacer length and solvent on diluted solutions of cationic isothiouronium polythiophenes

This contribution presents a study on two cationic isothiouronium polythiophenes (poly-3-(N, N-diethyl-S-iso-thiouronium) alkoxy-4-methyl thiophene), with alkoxy chains of different length in the 3-position of the thiophene ring, results of steady-state absorption and fluorescence spectroscopies in four solvents of different polarities: protic water, protic-protic water-isopropanol, protic-aprotic water-tetrahydrofuran and protic-non polar water-1,4-dioxane (all mixtures 0.5 v/v) are presented. Molar absorption coefficient (epsilon), quantum yield (phi(f)), spectral maxima (lambda(max), lambda(em)) and Stokes shift (Delta nu) are presented, and the effect of solvents on these parameters is discussed. Empirical optical and electrochemical energy levels were estimated using drop cast films on glass and on glassy carbon electrode, respectively. Density functional theory was used to gain supporting structural, energy and electronic information of different oligomers, simulating solvents of different polarity

Electrosynthesis of a copolymer containing C 60 in the main chain

Abstract The electrochemical synthesis of a copolymer consisting of phenylene vinylene units and C 60 was studied. The starting materials were ␣,␣,␣ ,␣ -tetrabromo-p-xylene and C 60 . The fullerene is introduced into the polymer synthesis as a film on the working electrode. The C 60 film is dissolved upon reduction and the reduced fullerene species interacts with the simultaneously reduced precursor at the electrode surface resulting in a film on the substrate. The coupling reaction between the reduced species leads to a material where the fullerene units are incorporated into the main polymer chain. The film formed is characterized by cyclic voltammetry and by FTIR, Raman and UV-vis spectroscopy. The charging discharging reaction of the copolymer film was studied by in situ ATR-FTIR. The spectroscopic results indicate short chains of copolymeric structure. Fluorescence spectra were recorded from films of the copolymer and from PPV. The fluorescence of PPV was quenched to one tenth of its origin in the copolymer film

Effect of Spacer Length and Solvent on the Concentration-Driven Aggregation of Cationic Hydrogen-Bonding Donor Polythiophenes

Aggregation of cationic isothiouronium polythiophenes with alkoxy-spacers of different lengths at the 3-position of the thiophene ring was studied in solvents of different polarities. Hydrogen-bonding capacity was assessed by steady-state absorption and fluorescence spectroscopy, whereas the aggregation in aqueous solutions was studied by electron paramagnetic resonance spectroscopy, using paramagnetic probes of different polarities. The two polymers displayed similar features in respect to conformation, effect of cosolvents on aggregation, unstructured absorption–fluorescence spectra, Stokes shifts when aggregated, solvatochromic effect, and self-quenching concentration. However, these polymers also showed different specific interactions with water, Stokes shifts in water, effect of the solvent on the extent of dominant state of the S1 level, and also different inner cavities and hydrophobic–hydrophilic surface area in aqueous solution aggregates. Water maximized the difference between the polymers concerning the effect of specific increases in concentration, whereas the presence of 1,4-dioxane generated almost identical effects on both polymers