Dual-emission luminescence thermometry using LaGaO3:TM3+, Ln3+ phosphors

The first biological window (650–950 nm) is the area within the NIR spectrum able to penetrate skin more effectively than shorter wavelengths.1 The TM3+, Ln3+ activator combination has attracted attention due excitation/emission within this wavelength range.2 In this investigation, a series of La1-xGa0.99O3: Cr0.01, Ndx phosphors (where x = 0.005, 0.01, 0.02) were synthesised by conventional solid-state methods and structurally characterised by Rietveld refinement of a structural model and powder diffraction data.3 Room temperature photoluminescence was undertaken with excitation spectra of both the Cr3+ and the Nd3+ showing energy transfer to the other emission centre alongside showing the characteristic Cr3+ broadbands, and sharp Nd3+ line excitations. Emission spectra showed both the Cr3+ 2E sharp peak at 729 nm, and the Nd3+ 4I3/2 4I9/2 emission of Nd3+ ca. 890 nm. Variable temperature thermometric analysis was undertaken, with the La1-xGa0.99O3: Cr0.01, Ndx (x = 0.02) sample exhibiting the emissions from the Cr3+ and Nd3+ centres at comparable intensities. Monitoring by luminescence intensity ratio (LIR) showed Cr3+ emission being quenched slower than Nd3+ emission. The phosphor produced a relative sensitivity of ~2.0% K-1 at 300 K, high absolute sensitivity, and a temperature resolution of 0.04 K at 300 K.ICOM&IWPPP 2022 : August 29 - September 2, 2022, Belgrad

Systematic and Controllable Negative, Zero, and Positive Thermal Expansion in Cubic Zr1–xSnxMo2O8

We describe the synthesis and characterization of a family of materials, Zr1–xSnxMo2O8 (0 < x < 1), whose isotropic thermal expansion coefficient can be systematically varied from negative to zero to positive values. These materials allow tunable expansion in a single phase as opposed to using a composite system. Linear thermal expansion coefficients, αl, ranging from −7.9(2) × 10–6 to +5.9(2) × 10–6 K–1 (12–500 K) can be achieved across the series; contraction and expansion limits are of the same order of magnitude as the expansion of typical ceramics. We also report the various structures and thermal expansion of “cubic” SnMo2O8, and we use time- and temperature-dependent diffraction studies to describe a series of phase transitions between different ordered and disordered states of this material

Bismuth zinc vanadate, BiZn2VO6: New crystal structure type and electronic structure

We report a combined experimental and computational study of the crystal structure and electronic properties of bismuth zinc vanadate, BiZn2VO6, known for its visible light photocatalytic activity. The crystal structure has been solved from laboratory powder X-ray diffraction data using the repeated minimisations from random starting values method. BiZn2VO6 adopts a new structure type, based on the following building blocks: corner- and edge-sharing ZnO4 tetrahedra, ZnO6 octahedra and VO4 tetrahedra, and Bi2O12 dimers. It is the only known member of the BiM2AO6 (M=Pb, Ca, Cd, Mn, Zn, Mg, Cu; A=V, P, As) family which does not appear to be structurally closely related to others. The electronic structure of BiZn2VO6, calculated by DFT methods, shows that it is an indirect gap semiconductor with a calculated band gap of 1.6 eV, which compares favourably to the experimentally measured value of 2.4 eV

Archaeometric study of 17th/18th century painted pottery from the Belgrade Fortress

The chemical and mineralogical composition of ceramic bodies, glazes and pigments, as well as the firing temperatures of main groups of Austrian period painted pottery excavated at the Belgrade Fortress on the territory of Serbia, two groups of Malhornware and one group of Anabaptist faience, were determined by a combination of powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, energy dispersive X-ray fluorescence (XRF) and micro-Raman spectroscopy. Investigated pottery was uncovered in the same archaeological context and dated the end of 17th/first decade of 18th century. The obtained mineralogical and chemical composition shows the similarities between the Malhornware groups that indicate a similar production technology. Use of calcareous clay fired at temperatures in the range 850–900°C indicates a different production technology for the Anabaptists faience. The compositional data treatment by multivariate statistical analysis reveals heterogeneity in the Anabaptist faience group of samples, suggesting potential interactions between the local potters and the Anabaptist communities

Double-deconvolution method for the separation of thermalised emissions from chromium-doped lanthanum gallate and its potential in luminescence-based thermometry

A series of LaGa1–xO3:Cr3+x phosphors (x = 0.002, 0.005, 0.01, 0.02, 0.04) were synthesised by solid-state reaction and structurally characterised by Rietveld refinement from powder X-ray diffraction data. Amongst the five compounds, that with x = 0.01 exhibited the highest photoluminescence quantum yield at room temperature, those with higher doping levels probably suffering from self-quenching of the luminescence. This compound was selected for study of the temperature-dependence of the optical properties. The emission spectra recorded over the range 300–600 K reveal distinct features: a broad band that initially increases with temperature, attributed to fluorescence from the 4T2 excited state, and a series of sharp peaks that monotonically decline with temperature, attributed to phosphorescence from the 2E. The thermometry capabilities of LaGa0.99O3:Cr0.01 were probed by the luminescence intensity ratio (LIR) method using the broad 4T2 band relative to the sharp 2E peaks. To overcome the difficulties associated with the significant overlap of the broad and sharp emissions of Cr3+, a novel method was applied in which the deconvolution of broad peaks was performed in two steps, by fitting the broad bands to the curve sections without the sharp peaks. The ratio of the deconvoluted 4T2 and 2E intensities gave an excellent fit to the Boltzmann distribution, with an energy gap between them of 2172 cm–1. The high relative sensitivity at room temperature of ca. 2.5% K–1 demonstrates very good potential of LaGa0.99O3:Cr0.01 for thermometry in the first biological window of transparency, relevant for in vivo biomedical applications

Na+ mobility in sodium strontium silicate fast ion conductors

We present the first direct evidence of Na-ion mobility in sodium strontium silicate fast ion conductors, based on variable temperature 23Na solid state NMR spectroscopy and spin-lattice relaxation measurements

Evidence of continuous pottery production during the late Byzantine period in the Studenica Monastery, a UNESCO World Heritage Site

A collection of 63 pottery shards excavated at the Studenica Monastery, Serbia, originating from two distinct cultural strata (late 12th until the late 13th century, and the 14th and the first half of 15th century) was subject of this work. Mineralogical and chemical composition of body and glaze and production technology of investigated pottery were determined combining optical microscopy, inductively coupled plasma-optical emission and wavelength dispersive X-ray fluorescence spectrometry, Fourier transform infrared and micro-Raman spectroscopy, high-resolution synchrotron powder X-ray diffraction and multivariate statistical analysis. In addition, clay rod with traces of glaze from the kiln found within the Monastery complex was investigated. The firing temperature was estimated at 600–700 °C for the most of cookware and at 800–1000 °C for tableware. Pottery, made of non-calcareous clay, was covered with transparent lead based glaze and copper and iron were used as colorants. Combining results of all used techniques no significant differences in mineralogical and chemical composition among samples from two cultural strata were identified indicating continuous pottery production process from 13th until 15th century in Studenica