Karl Gatterer

Optical spectroscopy of lanthanide ions in ZnO–TeO2 glasses

Zinc tellurite glasses of compositions 19ZnO-80TeO2-1Ln2O3 with Ln = Eu, Er, Nd and Tm were prepared by melt quenching. The absorption spectra were measured and from the experimental oscillator strengths of the f-->f transitions the Judd-Ofelt parameters ohm(lambda) were obtained. The values of the ohm(lambda) parameters are in the range usually observed for oxide glasses. For Nd3+ and Er3+, luminescence spectra in the near infrared were measured and the stimulated emission cross sections sigma(p) were evaluated for some laser transitions. The high values of sigma(p), especially for Nd3+, make them possible candidates for optical applications. Fluorescence line narrowing (FLN) spectra of the Eu3+ doped glass were measured at 20 K, and the energies of the Stark components of the 7F1 and 7F2 states were obtained. A crystal field analysis was carried out assuming a C2v site symmetry. The behaviour of the crystal field ratios B22/B20 and B44/B40 agrees reasonably well with the values calculated using the geometric model proposed by Brecher and Riseberg. The crystal field strength at the Eu3+ sites appears to be very low compared to other oxide glasses.

The floating water bridge

When high voltage is applied to distilled water filled in two glass beakers which are in contact, a stable water connection forms spontaneously, giving the impression of a floating water bridge. A detailed experimental analysis reveals static and dynamic structures as well as heat and mass transfer through this bridge.

Hypersensitivity and nephelauxetic effect of Nd(III) in sodium borate glasses

Abstract An investigation of the optical absorption spectra of 1 mol% Nd2O2 in sodium borate glasses with Na2O contents varying from 7.5 to 40 mol% is presented. The glasses were obtained by quenching melts consisting of Na2CO3, H3BO3, and Nd2O3 (900 to 1100°C, 1.5–2 h) between steel plates. The optical absorption spectra were recorded at 300 and 20 K. Special emphasis is laid on the positions, half-widths, intensities and shapes of the 4 I 9 2 → 2 P 1 2 and the hypersensitive 4 I 9 2 → 4 G 5 2 , 2 G 7 2 transitions. The observed property versus composition variations are discussed in terms of the covalency of the neodynamium-oxygen bond and of changes induced into the crystalline field around the Nd3+ ions by structural changes of the glass matrix. The shape of the hypersensitive transition is used for comparison with existing models on the rare earth environment in oxide glasses.

Preparation and Characterization of Chromium(III)-Activated Yttrium Aluminum Borate: A New Thermographic Phosphor for Optical Sensing and Imaging at Ambient Temperatures

A new thermographic phosphor based on chromium(III)-doped yttrium aluminum borate (YAB) is obtained as single crystals by high temperature flux growth and as a microcrystalline powder via solution combustion synthesis. The phosphor is excitable both in the blue (λmax 422 nm) and in the red part of the spectrum (λmax 600 nm) and shows bright NIR emission. The brightness of the phosphor is comparable to that of a well-known lamp phosphor Mn(IV)-doped magnesium fluorogermanate. At ambient temperatures, the Cr(III)-doped YAB shows high temperature dependence of the luminescence decay time, which approaches 1% per deg. The material shows no decrease in luminescence intensity at higher temperatures. The new phosphor is particularly promising for applications in temperature-compensated optical chemosensors (including those based on NIR-emitting indicators) and in pressure-sensitive paints.

Suitability of Nd(III) absorption spectroscopy to probe the structure of glasses from the ternary system Na2O–B2O3–SiO2

Abstract Optical absorption spectra of glasses from the ternary system Na 2 O–B 2 O 3 –SiO 2 with 20, 40, and 60 mol% SiO 2 and varying modifier contents containing 1 mol% Nd 2 O 3 were measured at cryogenic temperatures. The glasses were obtained by quenching the liquids of appropriate composition between steel plates. For comparison doped glasses from the binary systems Na 2 O–B 2 O 3 and Na 2 O–SiO 2 were included. The molar volumes and packing ratios of the doped ternary glasses were compared with those of undoped glasses with similar composition to make sure that the dopant ions do not affect the bulk glass properties. The position of the 4 I 9/2 → 2 P 1/2 transition was used to monitor the nephelauxetic effect and the hypersensitive 4 I 9/2 → 4 G 5/2 , 2 G 7/2 transition to monitor changes in the rare-earth environment with the glass composition. The observed changes of the spectral features are consistent with structural changes in the host glasses as proposed by models of these glasses derived from NMR and IR investigations on undoped glasses. Hence the suitability of Nd 3+ absorption spectroscopy to probe the structure of these glasses is established.

Growth, optical spectroscopy and crystal field investigation of YAl3(BO3)4 single crystals doped with tripositive praseodymium ☆

Single crystals of YAl3(BO3)4 doped with 1 and 10% Pr3+ were grown by spontaneous nucleation from a K2Mo3O10 and B2O3 flux. Polarised absorption and luminescence spectra in the visible, near infrared and infrared ranges were recorded at room and low temperatures on ground and polished samples of about 1 mm thickness. The microsymmetry of the Pr3+ sites is D3. The observed transitions were assigned and analysed on the basis of the selection rules for the D3 point group. A set of free ion and crystal field parameters in reasonable agreement with the observed energy level structure is reported. The possible applications of the material in the field of optical devices are considered.

Dynamics of the floating water bridge

When high voltage is applied to distilled water filled into two beakers close to each other, a water connection forms spontaneously, giving the impression of a floating water bridge (Fuchs et al 2007 J. Phys. D: Appl. Phys. 40 6112–4). This phenomenon is of special interest, since it comprises a number of phenomena currently tackled in modern water science. The build-up mechanism, the chemical properties and the dynamics of this bridge as well as related additional phenomena are presented and discussed.

Red light-excitable dual lifetime referenced optical pH sensors with intrinsic temperature compensation

Red light-excitable pH sensing materials are manufactured which rely on the use of a fluorescent seminaphthorhodafluor indicator and a luminescent inorganic phosphor as a reference. The phosphors, chromium(III)-activated lanthanide aluminium borates, benefit from chemical and photochemical robustness and are not affected by oxygen. Particularly, a dual lifetime referenced sensing material relies on Cr(III)-activated gadolinium aluminium borate which has low temperature dependence of the decay time. The second material is based on highly temperature-sensitive Cr(III)-doped yttrium aluminium borate and enables dual sensing of pH and temperature. Here, the phosphor simultaneously acts as a temperature probe and as a reference for the pH indicator. The adverse effects of temperature on the properties of the pH indicator are compensated for. The dynamic range of the sensors is optimized by varying the ratio of the components which makes the materials suitable for physiological measurements and for marine applications. The rather poor chemical and photochemical stability of the pH indicator at room temperature should be considered if prolonged measurements are performed.

Colour change of co-doped yttrium aluminium borate crystals under illumination with different white light sources

A colour change of doped YAB crystals and microcrystalline powders takes place upon illumination with different white light sources. This paper presents extensive experimental data on the new materials Ho,Nd:YAB; Ho,Cr:YAB, Nd,Cr:YAB and Ho,Nd,Cr:YAB, resulting in a chart providing the observed crystal colours and chromaticity differences of the materials under illumination with seven different types of white light sources. The microcrystalline powders could be used as coatings in order to produce a special colour changing effect. Furthermore, the colour table presented enables the observer to discriminate the investigated light sources at one glance.

Towards the chemical control of molecular packing: syntheses and crystal structures of three trans-(NiL4(NCS)2) complexes

Three nickel(II) isothiocyanato complexes of the formula trans-[NiL4(NCS)2] (L = ethylisonicotinate, methylisonicotinate and 4-benzoylpyridine) have been prepared: [Ni(ethylisonicotinate)4(NCS)2] (I), [Ni(methylisonicotinate)4(NCS)2] (II) and [Ni(4-benzoylpyridine)4(NCS)2] (III). All three complexes are monomeric and have a distorted octahedral geometry around Ni(II). Despite their apparent molecular similarity, the crystal density of (III) (1.454 g cm(-3)) is significantly higher than that of (I) and (II) (both 1.408 g cm(-3)), suggesting that the molecular packing is most efficient in (III). A study of the molecular Hirshfeld surfaces, together with density functional theory (DFT) calculations, provide insights into the origin of the molecular packing features, and it is suggested that the greater crystal density of (III) results from smaller intermolecular electrostatic repulsions.