Barbara Szpikowska-Sroka

Ultraviolet-to-visible downconversion luminescence in solgel oxyfluoride glass ceramics containing Eu 3+ :GdF 3 nanocrystals

GdF3 nanocrystals doped with Eu3+ ions in oxyfluoride glass ceramics were prepared by a solgel method. The structural properties were examined by x-ray diffraction measurements. The effects of gadolinium codoping on europium emission in the prepared solgel glasses and glass ceramics have been studied. The emission bands originating from the 5D0 state of Eu3+ ions are enhanced under excitation of Gd3+ ions by 273 nm line. The electric dipole 5D0→7F2 transitions were dominant in the samples before heat treatment, whereas magnetic dipole 5D0→7F1 transitions had a higher probability in the samples after annealing. The luminescence lifetime for the 5D0 level of Eu3+ ions in the samples after excitation at 273 nm is long lived in comparison to excitation at 393 nm and increased to 190%. Energy transfer from Gd3+ to Eu3+ was observed.

Influence of silicate sol–gel host matrices and catalyst agents on the luminescent properties of Eu3+/Gd3+ under different excitation wavelengths

Sol–gel silicate glasses co-doped with Gd3+ and Eu3+ ions were successfully obtained and the pronounced effect of the matrix composition on the energy transfer process from Gd3+ to Eu3+ was confirmed. Qualitative compositions of the examined matrices were varied while the europium and gadolinium ion concentrations were kept constant. Different chemical compositions of the sol–gel matrices were clearly marked by changes in the photoluminescent properties. The effect of gadolinium ions on the visible emission of europium ions has been studied. The characteristic emission bands corresponding to the 5D0 → 7FJ (J = 0–4) transitions of Eu3+ were registered. The emission of Eu3+ ions significantly increased during indirect excitation via the energy transfer process Gd3+ → Eu3+ (λexc = 273 nm) in comparison to direct excitation of Eu3+ ions (λexc = 393 nm). The beneficial influence of the energy transfer process on the 5D0 luminescence lifetimes of Eu3+ ions was definitely stated. The structure of the prepared silica sol–gel materials was examined using X-ray diffraction measurements (XRD) and FT-IR spectroscopic techniques. The formation of GdF3 and Gd2O3 nanocrystalline phases was confirmed.

Emission of Eu3+ in sol-gel oxyfluoride glass materials obtained by different preparation methods

Abstract Silica glasses doped with Eu 3+ ions prepared by sol-gel methods were investigated. The X-ray diffraction (XRD) was used to verify the nature of the studied systems. Excitation and emission spectra of Eu 3+ ions in sol-gel glass materials were detected. Red-to-orange luminescence intensity ratios R/O related to integrated intensities of 5 D 0 → 7 F 2 to 5 D 0 → 7 F 1 transitions and luminescence lifetimes for 5 D 0 state of Eu 3+ ions were determined. The results indicated that spectroscopic parameters for Eu 3+ ions strongly depended on reagents and their relative ratios used for sol-gel glass preparation.

Determination of L-ascorbic acid after chromatographic separation

A simple and accurate analytical procedure is proposed for determination of L-ascorbic acid after chromatographic separation. Optimum conditions for TLC separation of L-ascorbic acid were established. L-Ascorbic acid was detected by UV at λ = 254 nm. Spectrophotometric quantification was by means of a sensitive and simple method based on oxidation of leuco crystal violet to crystal violet. The absorbance of the crystal violet dye formed was measured at λ = 588 nm. The procedure was successfully used for determination of L-ascorbic acid in complex pharmaceuticals and in pepper juice samples. The results obtained were compared with those obtained by use of the Polish standard method.

Optical properties of silica sol-gel materials singly- and doubly-doped with Eu3+and Gd3+ ions

Abstract In present work, the optical and structural properties of silica sol-gel glasses and glass-ceramic materials singly- and doubly-doped with Eu 3+ and Gd 3+ ions were investigated. The optical properties of studied systems were determined based on absorption, excitation and emission spectra as well as luminescence decay analysis. Conducted studies clearly indicated a significant enhancement of visible emission originated from Eu 3+ ions as a result of changing the excitation mechanism, via Gd 3+ →Eu 3+ energy transfer. The luminescence intensity R-ratio was analyzed before and after heat-treatment process upon excitation at γ ex =393 nm and γ ex =273 nm. Moreover, the influence of excitation wavelength on luminescence decay time of the 5 D 0 excited state was also analyzed. The Gd 3+ →Eu 3+ energy transfer efficiencies for precursor and annealed samples were calculated based on luminescence lifetime of the 6 P 7/2 level of Gd 3+ ions. The X-ray diffraction measurements were conducted to verify the nature of obtained sol-gel materials. In result, the formation of orthorhombic GdF 3 nanocrystal phase dispersed in amorphous silica glass host was identified after annealing. Obtained results clearly indicated an incorporation of Eu 3+ activators into formed GdF 3 nanocrystals. Thus, conducted heat-treatment process led to considerable changes in surrounding environment around Eu 3+ ions. Actually, it was found that energy transfer phenomenon and heat-treatment process were responsible for significant improvement of Eu 3+ luminescence in studied sol-gel samples.

SPECTROPHOTOMETRIC DETERMINATION OF L-ASCORBIC ACID IN PHARMACEUTICALS

A simple and sensitive spectrophotometric method for the determination of L-ascorbic acid with leuco crystal violet is proposed. The determination is based on the oxidation of analyte by potassium iodate. The colourless oxidation products were formed in the quantity equivalent to iodide ions. The iodide ions react with the excess of iodate ions in acidic medium, to form free iodine which oxidized leuco crystal violet (LCV) to the liberated crystal violet (CV+) dye, showing maximum absorption at 588 nm. The absorbance was measured at pH of 4.1–4.2 in 1 cm cuvettes. Beer’s law was obeyed in the concentration range 0.5–4.0 μg/mL. The molar absorptivity of the coloured compound is 4.14 × 104 L/mol cm for L-ascorbic acid. The analytical parameters were optimized and the method was successfully applied to the determination of L-ascorbic acid in pharmaceuticals. The results were compared with those obtained by methods proposed in Polish Standard.

A simple and sensitive analytical method for the determination of thiamine in pharmaceutical preparations

A simple and sensitive method for spectrophotometric determination of thiamine with leucocrystal violet was elaborated. Spectrophotometric quantification based on the following reaction sequence: thiamine was oxidized with potassium iodate(V) to the colourless product and a stoichiometric amount of iodide ions was formed. The latter reacted with the excess of iodate(V) ions in acidic medium, to form free iodine which oxidized leucocrystal violet to the crystal violet dye. The absorbance of the crystal violet dye formed was measured at pH 4.1 ± 0.1 and 589 nm. The measured absorbance obeyed Beer’s law over the thiamine concentration range 0.4-2.4 μg/mL. The linear regression coefficients were a = 0.3339, b = −0.0001, and r = 0.9998 (for the general form of the linear equation y = ax + b). The apparent molar absorptivity of the coloured compound was 1.12 × 105 L/mol cm for thiamine. The limit of detection and limit of thiamine determination were found to be 0.19 and 0.26 μg/mL, respectively. Optimum reaction conditions providing maximum and constant absorbance were optimized. The procedure was successfully used to the determination of vitamine B1 in pharmaceutical formulations. The obtained results were compared with those obtained by the method proposed by Polish Standard.

Aerogel insulation materials for industrial installation: properties and structure of new factory-made products

In this article the comparisons of two new factory-made Chinese aerogel products with the Pyrogel® product, all available on the market, are presented. The aerogel products are in a flexible blanket form and all products are dedicated for high temperature applications. The properties of the samples such as their dimension stability, water vapour transmission and water absorption are also described. Additionally the microstructure and chemical composition of the products are analysed using SEM/EDS (scanning electron microscopy coupled with X-ray energy-dispersive spectroscopy). The differences in the maximum service temperature are presented. The internal self-heating of the aerogel samples is described and is compared to a similar effect observed in mineral wool samples. The results in the change of the thermal properties in a wide range of temperatures (+ 10–600°C) are shown. The obtained results are correlated with the mineral wool data. The correlation shows an advantage in a high-efficiency thermal performance of aerogel products compared to other insulation materials at high temperatures.Graphical Abstract

Spectrophotometric study of colour reaction of vanadium(IV) with Chrome Azurol S in the presence of cationic and non-ionic surfactants

The optimum conditions for the formation of complexes of vanadium(IV) with Chrome Azurol S (CAS) in the presence of cationic (benzyldodecyldimethylammonium bromide (ST)) and non-ionic (Triton X-100, Tween 20 and Brij 35) surfactants have been determined. The complexes are formed in weakly acid solution (optimum pH: 4.6, 4.0 and 3.9) and show the absorption maxima at 603, 600 and 598 nm, respectively. The highest sensitivity was obtained for the method based on quaternary system V(IV)-CAS-ST-Triton X-100 due to the higher CAS: V(IV) molar ratio in this complex than in binary and ternary complexes: V(IV)-CAS) and V(IV)-CAS-ST. The molar absorptivity of this system is 8.08 × 104 L/mol cm. The LOD and LOQ values are: 0.006 and 0.02 μg/mL, respectively. Beer’s law is obeyed in the range: 0.02–0.60 μg/mL of V. The precision (RSD = 0.51%) and accuracy (1.9%) are satisfactory. This method has been applied to the determination of vanadium in plant materials.

A new sensitive spectrophotometric determination of sodium 2-mercaptoethanesulfonate using leuco xylene cyanol FF

A simple and accurate spectrophotometric method for determination of sodium 2-mercaptoethanesulfonate (MESNa) with leuco xylene cyanol FF (LXCFF) has been developed. The proposed method is based on the reaction of MESNa with potassium iodate(V) in acidic medium to liberate iodine, which oxidizes leuco xylene cyanol FF to its blue form xylene cyanol FF. The xylene cyanol FF dye formed shows maximum and stable absorbance at pH 4.1–4.2. Absorbance of the obtained colored products was measured at 613 nm. The molar absorptivity, limit of detection and limit of determination of the method were found to be 3.64 × 104 L/mol cm, 0.29 and 0.33 μg/mL, respectively. The colour system obeys Beer’s laws in the range 0.4–4.0 μg/mL of MESNa. All the variables were studied in order to optimize the reaction conditions. The procedure was used for determination of MESNa in pharmaceutical preparations. Reliability of determination was confirmed applying standard iodometric method, recommended by European and Polish Pharmacopoeia.