Structural, luminescence properties and Judd-Ofelt analysis of rare-earth doped calcium-sulfoborophosphate and barium-sulfoborophosphate glasses

Glass samples of undoped calcium-sulfoborophosphate and barium-sulfoborophosphate with chemical composition of xCaSO4-30B2O3-(70-x)P2O5 and xBaSO4- 30B2O3-(70-x) P2O5 with 15 ≤ x ≤ 35 mol% were prepared using melt quenching method. A series of glass samples doped with rare earth (RE = Dy2O3, Sm2O3 and Eu2O3) with the chemical compositions of 25CaSO4-30B2O3-(45-y)P2O5–yRE and 25BaSO4-30B2O3-(45-y)P2O5–yRE with 0.1≤y≤1.0 mol% were also prepared by melt quenching method. The amorphous phase of the glass samples were characterized by X-Ray diffraction (XRD) method, while the structural features of the samples were measured using Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. The optical properties of glass samples were characterized by ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy and luminescence spectroscopy. The amorphous phase of the glass samples was confirmed by the diffuse broad XRD pattern. The infrared spectral measurements revealed the presence of vibrational groups of P-O linkage, BO3, BO4, P-O-P, O-P-O, S-O-B (sulfoborate network) groups and the bending B-O-B units in sulfoborophosphate structural network of glass samples. The Raman spectra also revealed the coexistence of structural units of BO4, SO42-, PO43-, and P-O-P in sulfoborophosphate glass samples. The luminescence spectra of Dy3+ ions doped glass samples exhibit four emission bands at around 482 nm, 572 nm, 662 nm and 685 nm, which correspond to the 4F9/2→6H15/2, 4F9/2→ 6H13/2, 4F9/2→6H11/2 and 4F9/2→6H9/2 transitions, respectively. The emission spectra of glass samples doped with Sm3+ ions show dominant peaks at around 559 nm, 596 nm, 642 nm and 709 nm which correspond to the transitions of 4G5/2→6H5/2, 4G5/2→6H7/2, 4G5/2→6H9/2 and 4G5/2→6H11/2, respectively. Meanwhile, glass samples doped with Eu3+ ions show emission spectra peaks around 589 nm, 611 nm, 651 nm and 701 nm which correspond to the transitions of 5D0→7F1, 5D0→7F2, 5D0→7F3 and 5D0→7F4, respectively. Absorption and emission spectra are used to evaluate the Judd-Ofelt intensity parameters and radiative transition probabilities, branching ratios and stimulated emission cross-sections of the three rare-earth ions (Dy3+, Sm3+, and Eu3+) doped glass system. Based on this study, it can be concluded that the structural network features of calcium sulfoborophosphate and barium sulfoborophosphate glasses are similar, despite of different modifier. The incorporation of sulphate and rare-earth ions into the glass network show enhancement of chemical and physical stability, in addition to improving optical properties performance of the prepared glasses such as having high value of branching ratio, stimulated cross-section, gain bandwidth and optical gain. In view of this, calcium sulfoborophosphate and barium sulfoborophosphate glasses could be suggested as promising luminescent host material for solid-state lighting device application

An overview of soil erosion modelling

Soil erosion is one of the most important environmental issues in natural and synthetic territories. It can lead to loss of fertility, slope instability, soil truncation; etc. which causes irreversible effects on the poorly renewable soil resource. Therefore, understanding the key parameters and factors to model soil erosion will enable the conservation of soil system goods, services and resources, and will avoid the damage outside of fields caused by transported and accumulated sediments and water. In view of this, a review was carried out on previous studies to examine the concept of soil erosion and review various soil models widely used in literature. It was found that several models are used for soil assessment and prediction and these models are classified into physical (e.g. WEPP), conceptual (SEDNET) and empirical (USLE). The Universal Soil Loss Equation (USLE) and its modifications were found to be the most commonly used soil erosion models due to its simplicity, ease of use and the ability to integrate the various ecosystem parameters successfully. Furthermore, it was found that one of the major limitations associated with the use of models is lack of data for validation especially in large areas where obtaining ground data is not feasible. Although some researchers have suggested the use of correlation between modeled erosion results with factors such as land cover and management factor and soil erodibility factor as well as results of land use change analyses as alternatives for validation purpose. Others correlate the predicted soil erosion results with that of sediment yield. Some validated their soil erosion data with results of land use change analyses, slope length and slope steepness factor, land cover and management factor and soil erodibility factor. However, there is still ambiguity in the knowledge of our understanding as to which soil erosion prediction model to use. Keywords: soil erosion, model, validation, USLE, RUSL

Structural and luminescent characteristic of Sm3+ doped magnesium sulfide borate orange-red phosphor for white LED

Polycrystalline compositions based on MgO, SO3 and B2O3 have both scientific and technological importance because of their useful applications. Doping with rare earth elements not only due to a rearrangement in the structure, but also to variation in the luminescence properties. Magnesium sulfide borate doped samarium oxide (MgSBO3:Sm3+) phosphors were prepared by solid state reaction and their structural and luminescence characteristic were studied and reported. IR and Raman spectral studies have been made to explore the presence of functional groups and various structural units in the prepared Polycrystalline. The formation of SO4, BO4, BO3, B-O-B and S-O-B structural units have been investigated. The emission and excitation properties were studied. And the results show that the emission and excitation spectra of these phosphors can be excited by ultraviolet (UV) 341, 370 and 403 nm light, and emit green, yellow and red light with intense peak at 601 nm, which are nicely in accordance with the widely applied near- UV LED chip. The emission spectral intensity of Sm3+ ions in the titled phosphors increases up to 1 mol% of Sm3+ ions and then decreases for 1.5 mol%. These results indicate that MgSBO3:Sm3+phosphor could be a potential suitable orange-red emitting phosphor candidate for white LEDs with excitation of a ~403 nm near UV LED chip

Structural characterization of sulphate borophosphate glasses containing calcium oxide

Increasing demands for better perfoming glasses have lead to current investigating of the sturctural properties of glasses for optimum performances. Calcium sulphate borophosphate glasses of different compositions were prepared using melt quenching technique. The glass forming ability and stability were checked using Differential thermal analyzer (DTA). Density and molar volume had been evaluated and analyzed. From the results of XRD, the absent of discrete and continuous sharp peaks confirmed the amorphous nature of the glass compositions while the results from both IR and Raman revealed the existence of SO4, BO4, BO3, P-O-P and PO43-. Addition of CaSO4 to borophosphate influenced the conversion of the dominant BO3 groups to BO4 groups. The structure of the samples was mainly based on metaphosphate, diphosphate and BO4 units, which became depolymerized with addition of CaSO4 content. The glass forming ability and thermal stability were found to increase with an increase in the concentration of modifier content. Glass density and molar volume is found to be between 2.146 to 2.314 gcm-3 and 45.794 to 48.880 m3mol-1 respectively. It is observed that the density of glass increased while the molar volume also increased with respect to increase in concentration of CaSO4 in the glass compositions. We analysed our data using different mechanisms and compared the results with previous works. Our findings show that this glass could be beneficial and considered as a good candidate for optical devices applications

Physical and optical properties of calcium sulfate ultra-phosphate glass-doped Er2O3

The influence of erbium on physical and optical properties of calcium sulfate ultra-phosphate glass was investigated using conventional melt quench process. Selected samples of composition 20CaSO4 (80 - x) P2O5- xEr2O3 with 0.1 ≤x ≤ 0.9 mol.% were prepared and assessed. X-ray diffraction (XRD) techniques were used to confirm the amorphous nature of the said samples. The structural units of phosphate-based glass were assessed from Raman spectra as ultra-(Q3), meta-(Q2), pyro-(Q1) and orthophosphate (Q0) units. Depolymerization process of the glasses was testified for higher calcium oxide content and UV-visible for optical measurement. Thermal analysis have been investigated by means of thermogravimetric analysis. The results show the decomposition of materials in the temperature range of 25°C-1000°C. Er3+ absorption spectra were measured in the range of 400-1800nm. PL measurement was carried out in order to obtain the excitation and emission spectra of the samples. The emission spectra excited at 779nm comprises of 518nm, 550nm and 649nm of transition 4F9/2, 4S3/2 and 2H11/2 excited states to 4I15/2 ground state. In physical properties, the density calculated using Archimedes method is inversely proportional to molar volume with increase in Er3+ ions. Optical bandgap (Eg) were determined using Tauc's plots for direct transitions where Eg (direct) decreases with increase in erbium content. The refractive index increases with decreasing molar volume; this may have a tendency for larger optical bandgap. The result obtained from the glass matrix indicates that erbium oxide-doped calcium sulfate ultra-phosphate may give important information for wider development of functional glasses

Studies of H2 storage efficiency of metal-doped carbon nanotubes by optical adsorption spectra analysis

Due to the recent demands to replace fossil fuels with hydrogen, researchers are making many attempts to develop new materials to store hydrogen energy. Hydrogen is considered a potential candidate to replace fossil fuels due to its non-toxic, massless, and more efficient properties. This research has investigated the enhancement of the hydrogen storage capabilities of armchair single-walled carbon nanotubes (SWCNTs) through the separate doping of transition metals such as osmium (Os) and iron (Fe). The studies were performed with quantum simulation codes implemented in Quantum ESPRESSO and thermo_pw based on density functional theory (DFT), plane waves and pseudopotentials. The obtained results show that Os-doped SWCNTs are more suitable for H2 storage than Fe-doped SWCNTs due to the almost equal energy loss with and without H2 adsorption. Furthermore, lower adsorption in perpendicular directions indicated that the adsorbed H2 molecules aligned parallel to the nanotube axes. This further confirmed that the SWCNT nanotube system had a higher aspect ratio in parallel directions. Overall, it has been observed that transition metal doping increases the efficiency of the hydrogen storage potential of armchair SWCNTs compared to other doped metals. In general, the co-doping of SWCNT with osmium and nitrogen atoms increases the adsorption capability of H2 molecules