In order to elucidate the effect of europium content on the optical and luminescent properties of borogermanate glasses, a series of Eu 3+ doped 30B 2 O 3 -40GeO 2 -(30-x)Gd 2 O 3 glasses with various doping levels (x=1-9 mol%) have been synthesized and studied with transmission, absorption, photoluminescence and decay time measurements. The transmission spectra proved that the title glasses maintained a high transparency about 80% in the 440 to 900 nm region. Based on the absorption spectra, the optical band gaps obtained from Tauc's plot can be narrowed by increasing content of Eu 3+ . From the photoluminescence spectra, the strongest red emission has been observed from the 5 D 0 → 7 F 2 level of Eu 3+ ions in borogermanate glasses. The strongest emission and excitation intensities of Eu 3+ ions are at the doping level of x=7 mol% and then these intensities decrease due to concentration quenching. The red to orange ratio (R/O) of 5 D 0 → 7 F 2 to 5 D 0 → 7 F 1 transitions has been investigated to predict the local environment of Eu 3+ ions. Judd-Ofelt (J-O) analyses have been performed from the emission spectra. The values of R/O and Ω 2 present an increase with increasing doping level, indicating the lower symmetric environment for Eu 3+ ions and higher covalency for Eu-O bond. The emission efficiency calculated from J-O theory is 75% at x=2 mol%. The decay time curves of 6 P 7/2 → 8 S 7/2 transition of Gd 3+ ions and 5 D 0 -7 F 2 transition of Eu 3+ ions confirm the energy transfer from Gd 3+ to Eu 3+ ions.
In this work, effects of compaction pressure on the structural and superconducting properties of BSCCO ceramic superconductors were investigated. The study was carried out on two systems which were, System I: Bi 1.7 Pb 0.3 Sr 2 Ca 2 Cu 3 O y and System II: Bi 1.6 Pb 0.3 Ag 0.1 Sr 2 Ca 2 Cu 3 O y , respectively. Ceramic powders were prepared by conventional solid-state reaction method and sintered at 850°C after compaction at five different pressures in the 150-750 MPa range. Critical temperatures of samples were determined by resistivity-temperature determinations made by four-point probe method in liquid nitrogen conditions. XRD analysis was conducted by powder X-ray diffraction method. Morphology of the grains present in the samples were determined by using scanning electron microscope (SEM) photographs at 2 K× and 2.5 K× magnifications for System I and System II, respectively. Sintered densities of the superconducting ceramics were measured by Archimedes water displacement method and unit cell parameters were additionally obtained from XRD data. T c values for System I was determined to be in the 109-115 K with sample D having the highest T c of 115 K while T c varied in the 104-109 K range and sample B had the highest T c value of 109 K for System II. The transition width, which is a sign of the purity of the samples, was determined to be narrow for both systems. The data obtained from X-ray diffraction measurements have shown that 2223 high-T c phase was dominant in both systems. The determination of the optimum pellet compaction pressure for BSCCO ceramic superconductors was the main purpose of this work. The results of this work indicated that compaction at around 450 MPa improves the superconducting and structural properties of the BSCCO ceramic superconductors.
In this paper the influence of different heating rates on thermoluminescence (TL) kinetics, glow-peak temperatures, heights and integrated TL intensities of the main glow peak of recently produced Mg2SiO4 : Tb dosimeters are reported. The TL properties of the phosphor were investigated after β-irradiation at room temperature. Glow curve shape, peak shape, repeated initial rise and variable heating rate methods were used to analyse the TL kinetics of the main glow peak at 473 K. Results show that the TL glow peak of Mg2SiO4 : Tb phosphor obeys second-order kinetics. Analysis of the main dosimetric peak by using the methods mentioned above revealed that activation energy (E) is about 1 eV and the pre-exponential factor (s) is in the range 1010–1011 s−1. In addition it is ascertained that the glow-peak temperature increases with heating rate. The glow-peak height showed two maxima in the heating rate range investigated. The behaviour of the integrated TL intensities and the maximum glow-peak temperatures related to the heating rate have been discussed in terms of thermal quenching and clustering formation.
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