Analysis Of Time-resolved Spectra Research Articles

Enhancement of Crystal Growth in Molten Salts by a Cocrystallization Agent: Synthesis and Luminescent Properties of Ce3+- and Eu2+-Doped La3(SiS4)2I.

In this study, we present the growth of large Ln3(SiS4)2I (Ln = La, Ce) crystals, both undoped and doped with Ce and Eu. The synthesis process involves the utilization of an arc-melted precursor in conjunction with sulfur and KI. We investigate the role of Zr, Nb, Mo, and Ir as cocrystallization agents, facilitating the growth of relatively large (up to 6-7 mm) crystals. Our study suggests that Mo effectively acts as a cocrystallization agent for the synthesis of the Ln3(SiS4)2I and Ce- and Eu-doped La3(SiS4)2I phosphors. We confirmed the phase purity and crystal structure through powder XRD and single-crystal XRD analyses. The Ce- and Eu-doped compositions exhibit broad-spectrum transitions from UV to visible regions. Photoluminescence spectroscopy analysis reveals distinct emission bands for Ce-doped La3(SiS4)2I at 430 and 490 nm within the bluish region (0.15, 0.22 coordinates on the 1931 CIE chromaticity diagram) upon excitation at 375 nm. Conversely, Eu-doped La3(SiS4)2I demonstrates an emission band at 578 nm in the yellow-orange (0.45, 0.51) region following excitation at 450 nm. Analysis of time-resolved spectra indicates multiple emissive bands contributing to the photoluminescence spectra. The average half-life of emission bands suggests fluorescence for (La1-xCex)3(SiS4)2I and phosphorescence for (La1-xEux)3(SiS4)2I phosphors.

Generating pure red and near white light in NaLaF4 microcrystal by controlling site-selective luminescence of Eu3+ and Tb3+ dopant ions

Here in this work, we aim to develop both red and near white light emitting phosphor materials using Eu3+ and Tb3+ as co-dopant ions and NaLaF4 as host matrix. It was observed that both Na and La atom possess two different types of lattice sites having different co-ordination and symmetry. We have theoretically calculated the substitution energies for Eu3+ and Tb3+ ions for all the available lattice sites and found that the preference of distribution of the dopant ions into these lattice sites is different. While Eu3+ ion prefers 9-coordinated Na1/La2 site and 6-coordinated Na2 site, Tb3+ prefers 9-coordinated La1 site. This is also reflected in the PL study of both pure Eu3+ and Eu3+-Tb3+ co-doped compounds. Substitution of Eu3+ ion at Na2 site results in short-lifetime value and highly intense red ED line as observed from time resolved spectra analysis at different delay time. On contrary, its lifetime value was found to be higher at 9-coordinated La2 site and resulting higher intense orange MD line. Defect centres, which are being created due to charge imbalance during substitution at Na site, is solely responsible for such behaviour. Increasing concentration of Eu3+ ions also resulted in higher red colour purity of the Eu3+ doped compound due to more defect induced asymmetry surrounds Eu3+ ion. For the Eu3+-Tb3+ co-doped compounds, the Tb3+→Eu3+ energy transfer dynamic is responsible for tuneable emission colour characteristics from white light to red. From lifetime study with varied concentration of Tb3+ ion, we have observed that the possibility of charge transfer from Tb3+ ion at Na-site (Tb3+Na1) to Eu3+ ion at Na2 (Eu3+Na2) is more compared to that from Tb3+La2 to Eu3+Na2.

The cooling phase of Type I X-ray bursts observed with RXTE in 4U 1820−30 does not follow the canonical F ∝ T4 relation

We analysed the complete set of bursts from the neutron-star low-mass X-ray binary 4U 1820-30 detected with the Rossi X-ray Timing Explorer (RXTE). We found that all are photospheric radius expansion bursts, and have similar duration, peak flux and fluence. From the analysis of time-resolved spectra during the cooling phase of the bursts, we found that the relation between the bolometric flux and the temperature is very different from the canonical F - T^4 relation that is expected if the apparent emitting area on the surface of the neutron star remains constant. The flux-temperature relation can be fitted using a broken power law, with indices 2.0$\pm$0.3 and 5.72$\pm$0.06. The departure from the F - T^4 relation during the cooling phase of the X-ray bursts in 4U 1820-30 could be due to changes in the emitting area of the neutron star while the atmosphere cools-down, variations in the colour-correction factor due to chemical evolution, or the presence of a source of heat, e.g. residual hydrogen nuclear burning, playing an important role when the burst emission ceases.

Photoluminescence characteristics of ZnO doped with Eu 3+ powders

In this work, we have investigated the photoluminescence spectra of europium-doped zinc oxide crystallites prepared by a vibrating milled solid-state reaction method. X-ray diffraction, scanning electron microscopy, luminescence spectra and time-resolved spectra analysis were used to characterize the synthetic ZnO:Eu 3+ powders. XRD results of the powders showed a typical wurtzite hexagonal crystal structure. A second phase occurred at 5 mol% Eu 2O 3-doped ZnO. The 5D 0– 7F 1 (590 nm) and 5D 0– 7F 2 (609 nm) emission characteristics of Eu 3+ appeared after quenching with more than 1.5 mol% Eu 2O 3 doping. The Commission Internationale d’Eclairage (CIE) chromaticity coordinates of a ZnO:Eu 3+ host excited at λ ex=467 nm revealed a red-shift phenomenon with increase in Eu 3+ ion doping. The lifetime of the Eu 3+ ion decreased as the doping concentration was increased from 1.5 to 10 mol%, and the time-resolved 5D 0→ 7F 2 transition presents a single-exponential decay behavior.

Parameter precision in global analysis of time-resolved spectra

By means of simulation parameter estimation in global analysis of time resolved spectra was studied. Kinetic, spectral as well as spectrotemporal models were used to describe a system consisting of an inherent mixture of components whose concentrations change with time. With a single component the parameter precision did not differ between the different model types. With two or more components the precision decreases with a kinetic or spectral model because of overlap between concentration profiles or spectra of the components. However, with a spectrotemporal model the decrease is much less, and equals zero with zero spectral overlap.