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Wide band gap niobium oxides are particularly important for electronic device applications. Two types of NbO powders were sintered between 300 and 1100 °C. The structural characterization of the pellets, performed by X-ray diffraction measurements and Raman spectroscopy, revealed the appearance of the NbO and T-, B-, and H-Nb2O5 polymorphs, depending on the sintering temperature. The optical characterization was complemented with absorption measurements and photoluminescence, where it was possible to identify a bandgap of 3.5 eV. A strong dependence of luminescence on the sintering temperature and therefore of the niobium oxide crystalline phases nature was observed. The influence of the morphological and structural characteristics on the dielectrical properties, at room temperature and in the low frequency range (<100 MHz), was studied. The sample with the H-Nb2O5 polymorph presents higher dielectric constant (∼55) than the samples with T- and B-Nb2O5 (∼25).

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Er3+ and Er3+/Yb3+ melilite-based SrLaAl3O7 (SLA) phosphors were synthesized by a facile Pechine method. The differences in emission intensities of 4I13/2 → 4I15/2 transition in NIR region when excited with Ar+ and 980 nm lasers were explained in terms of energy transfer mechanisms. Temperature and power dependence of upconversion bands in the visible region centered at 528, 548 and 660 nm pertaining to 2H11/2, 4S3/2 and 4F9/2 → 4I15/2 transitions were investigated. Fluorescence intensity ratio (FIR) technique was used to explore temperature sensing behaviour of the thermally coupled levels 2H11/2/4S3/2 of Er3+ ions in the phosphors within the temperature range 14–300 K and the results were extrapolated up to 600 K. Anomalous intensity trend observed in Er3+ doped SLA phosphor was discussed using energy level structure. Cytotoxicity of phosphors has been evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay in Bluegill sunfish cells (BF-2). The non-cytotoxic nature and high sensitivity of the present phosphors pay a way for their use in vitro studies and provide potential interest as a thermo graphic phosphor at the contact of biological products.

Magnetic properties of crystallized iron phosphate glasses and relationship between structural and magnetic properties modifications that occur during crystallization have been investigated. Iron phosphate glass exhibits the spin‐glass (SG) behavior and represents a prototype of solid with disordered spatially distributed magnetic moments. Glass of the composition 43Fe2O3–57P2O5 (wt%) was heat‐treated in air at 893, 923, and 1073 K for 24 h. The samples were studied using X‐ray diffraction, Raman spectroscopy, and dc magnetic measurements. The magnetic measurements show dominant antiferromagnetic (AF) interactions for all samples. The starting glass exhibits SG behavior, whereas magnetic behavior of samples heat‐treated at 893 and 923 K, which contain Fe3(P2O7)2 crystalline phase embedded in glass matrix, is ascribed to a mixture of superparamagnetism and SG behavior. In the sample heat‐treated at 1073 K, several peaks in the magnetization curves were observed which correspond to the various crystalline phases present in the sample: Fe3(P2O7)2, Fe4(P2O7)3 and Fe(PO3)3. Hysteresis loops show paramagnetic behavior at 300 K. Small curvature is present at low temperature (5 K) that can be ascribed to the AF ordering in the samples.

In this work, EuNbO 4 samples were prepared, in the shape of fibres, by the laser floating zone (LFZ) technique. The fibres grown at pulling rates below 20 mm h À1 are transparent and monophasic, crystallizing in a monoclinic structure. At higher growth rates, non-stoichiometric europium orthoniobate phases were promoted. The physical properties analysed in this work were the electric, dielectric and photoluminescence (PL) properties. For the fibre grown at 2.5 mm h À1 , the dc conductivity shows a value of 5.97 Â 10 À12 S m À1 and the ac conductivity, at 1 MHz and 300 K, is 3.08 Â 10 À4 S m À1 . Under the same experimental conditions the dielectric constant is $39 and the loss tangent $0.14, also presenting a relaxation phenomenon centred at $120 kHz. An ionic polarization type behaviour was identified from the dielectric measurements, which justifies the temperature independent behaviour of the dielectric constant. This type of polarization was assigned to the NbO 4 units. PL measurements with ultraviolet excitation reveal the intra-4f 6 transitions of Eu 3+ ions in the fibres, exhibiting narrow intraionic lines as expected for single crystal materials. From the PL spectra at low temperature, it was possible to identify multiple europium related centres, from different local site symmetry and/or environment. The luminescence of Eu 3+ was found to be preferentially excited via a broad excitation band peaked at $280 nm.

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