Search

A series of Sm3+-doped magnesium borate glasses were prepared using the melt quenching and characterized to determine the effects of various Sm3+ contents on their optical traits. The absorption and luminescence spectra of the glasses revealed ten and four significant peaks, respectively. In addition, the experimental results on the optical properties were validated using the Judd-Ofelt (J−O) analyses. The obtained J−O intensity parameters (Ωλ with λ = 2, 4, 6) confirmed the structural changes in the host network due to the Sm3+ doping. The value of Ω2 for the studied glasses indicated the covalent and asymmetric nature of the Sm3+− O2 linkages. The achieved J−O radiative parameters (quality factor, branching ratio and stimulated emission cross-section) were highest for the glass made with 0.5 mol% of Sm3+, demonstrating its lasing potency. The proposed glass compositions may be beneficial for the photonic devices.

This paper reports the luminescence potential of the dysprosium ion (Dy3+)-doped (varying contents from 0.1 to 1.0 mol%) magnesium borate glasses prepared by the melt-quenching method. As-quenched samples were characterized systematically to determine the effects of various Dy3+ contents on their structure, physical and optical traits. The Judd−Ofelt (J−O) intensity parameters (Ω2, Ω4, Ω6) and radiative properties of the best sample (with 0.7 mol% of Dy3+ doping) was evaluated to complement the experimental optical data. The studied glasses revealed three luminescence emission peaks at 382 nm (4F9/2→6H15/2, intense Blue), 572 nm (4F9/2→6H15/2, intense Yellow) and 661 nm (4F9/2→6H11/2, weak Red) under the excitation wavelength of 347 nm. The emission intensity was first increased up to the Dy3+ content of 0.7 mol% and then quenched. The observed luminescence intensity quenching was due to the resonant energy transfer from the excited state to the neighbouring ground state of Dy3+. The obtained high value of Ω2 signified the strong degree of covalency between the Dy3+ and ligand environment. The optimum glass sample (with 0.7 mol% of Dy3+) showed higher values of the branching ratio and stimulated emission cross-cross section for the 4F9/2→6H15/2 (yellow) emission transition, indicating its potential as bright yellow luminescent material and high gain visible laser applications.

Numerous studies have shown the interesting properties of trivalent lanthanide ions when doped in different types of glasses. This article examines the physical, structural and optical properties of series of strontium magnesium borate glasses doped with dysprosium ion (Dy3+) and synthesized using the melt-quenching technique. Physical and optical properties such as density, molar volume, ion concentration, molar refractivity, polaron radius, reflection loss, inter-nuclear distance and molar polarizability for each concentration of the dopant were calculated and reported. The results revealed diverse variations in density with other measured parameters. The amorphous behaviour of the glass samples was confirmed by X-ray diffraction spectroscopy. FTIR spectra measurements revealed the presence of various functional groups and their associated assignments. Optical properties of the activated glass samples with different concentrations of Dy3+ were determined by measuring the absorption and luminescence spectra in the visible region. The UV–Vis–NIR spectrophotometer analysis indicated the presence of eight inhomogeneous transition bands in various positions and intensities with hypersensitive transition at 1260 nm (6H15/2 → 6F11/2). The experimental oscillator strength (fexp) for each calculated absorption band showed higher magnitudes at hypersensitive transition. The optical energy band gap in the current work showed a decrease in values with increasing ion concentrations. The luminescence spectra of the prepared glass phosphors showed three unique transitions at 4F9/2 → 6H15/2 (490 nm), 4F9/2 → 6H13/2 (585 nm) and 4F9/2 → 6H11/2 (689 nm).

The application of machine learning algorithms to the detection of fraudulent credit card transactions is a challenging problem domain due to the high imbalance in the datasets and confidentiality of financial data. This implies that legitimate transactions make up a high majority of the datasets such that a weak model with 99% accuracy and faulty predictions may still be assessed as high-performing. To build optimal models, four techniques were used in this research to sample the datasets including the baseline train test split method, the class weighted hyperparameter approach, and the undersampling and oversampling techniques. Three machine learning algorithms were implemented for the development of the models including the Random Forest, XGBoost and TensorFlow Deep Neural Network (DNN). Our observation is that the DNN is more efficient than the other 2 algorithms in modelling the under-sampled dataset while overall, the three algorithms had a better performance in the oversampling technique than in the undersampling technique. However, the Random Forest performed better than the other algorithms in the baseline approach. After comparing our results with some existing state-of-the-art works, we achieved an improved performance using real-world datasets.

Intense visible emissions from dysprosium (Dy3+) ions doped glasses became prospective for diverse technological applications. In this paper, physical, optical and structural properties of magnesium borate glasses doped with varied concentrations of Dy2O3 were examined. Such glasses were synthesised by melt quenching method and characterized at room temperature using several analytical techniques. Luminescence and absorption spectra (in the visible region) of as-quenched samples were used to evaluate the physical and optical properties. XRD pattern confims the amorphous state of as-quenched samples. The Fourier transform infrared (FTIR) spectra of glasses reveal various bonding vibrations assigned to different functional groups. UV-vis-NIR spectra disclose eight absorption bands accompanied by a band for hypersensitive transition positioned at 1260 nm (6H15/2 → 6F11/2). The values of direct and indirect optical energy band gap of the studied glasses are decreased with the increase of Dy3+ ion contents. The photoluminescence spectra of all glasses under the excitation of 380 nm display two prominent emission bands centred at 497 nm (4F9/2 → 6H15/2, blue) and 587 nm (4F9/2 → 6H13/2, green). The achieved intense luminescence from the proposed glass composition may be beneficial for solid-state laser applications.

Two new series of strontium magnesium borate glasses with Dy3+ and Sm3+ activation (both in the concentration range of 0.1–1.0 mol%) were prepared using the standard melt-quenching and characterized. The optical and physical properties of these singly impurity-doped glass series were compared. The optical and physical properties of these glasses were determined in terms of the density, molar volume, optical band gap, absorption and emission intensities, oscillator strength, refractive index and molar polarizability. The XRD analyses confirmed the amorphous nature of the as-quenched samples. The EDX spectra revealed the actual elemental compositions and FESEM images showed the samples homogeneity without cracks. The UV–vis-NIR absorption spectra of the Dy3+- and Sm3+-doped glasses showed nine and ten characteristics bands respectively. The PL spectra of the Dy3+- and Sm3+-doped glasses displayed three ((at 481 nm, blue; 570 nm, yellow; and 661 nm, red) four (559, 596, 643 and 709 nm) significant peaks, respectively. The lasing potentials of the Dy3+- and Sm3+-doped glasses were compared via Judd-Ofelt evaluation. The values of branching ratio and stimulated emission cross-section for the 4F9/2 → 6H13/2 transition in Dy3+ and 4G5/2 → 6H7/2 transitions in Sm3+ was maximum, indicating their effectiveness towards photonic devices assembly. The studied glasses have demonstrated high viability for the cutting-edge innovations in the solid―state lighting and high gain optical fibre construction.

Some new type of strontium magnesium borate glass system doped with Dy3+ (various contents 0.1, 0.3, 0.5, 0.7 and 1.0 mol%) were produced using the conventional melt-quenching. Obtained glasses were thermally stable, highly transparent, and moisture resistant. As-prepared samples were characterized to determine their spectroscopic traits. The Judd-Ofelt (J-O) intensity Ωλ (λ = 2, 4, 6) and radiative parameters were calculated to validate the experimental results on the optical characteristics. The XRD pattern of the as-quenched samples verified their glassy nature, FESEM images showed uniform textures and EDX analyses detected the presence of appropriate constituents in the host matrix. Glass containing 0.7 mol% of Dy3+ revealed the optimum optical traits where the luminescence emission intensity was attenuated beyond this content. The optical gain for two intense emission transitions (4F9/2→6H15/2 and 4F9/2→6H13/2) was evaluated. The values of Ωλ (λ = 2, 4, 6) determined the ionic nature of the bonding and symmetry environment of the Dy―ligand matrix based on the viscosity and rigidity of the host glass. The 6H15/2→6F11/2 transition was hypersensitive. The ratio of the yellow to blue (Y/B) emission intensity less than unity indicated the lower degree of covalence between Dy3+ and O2− ions thereby makes these glasses effective for the near UV―LEDs. The higher values of the branching ratio (≥ 50 %) and stimulated emission cross-section enabled the proposed glass composition potential for the optical amplifiers and fibres fabrication. The resonant energy transfer and cross-relaxation processes in the Dy3+ were attributed to be responsible for the improved optical features.