RESUMEN

In this theoretical study, the potential of KGeCl3 was investigated as a lead-free perovskite active layer for perovskite solar cells. Calculations of the structural, electronic, elastic, optic, and thermoelectric properties of KGeCl3 in its cubic, tetragonal, and orthorhombic phases were performed using the generalized gradient approximation (GGA) within the wien2k package. The findings demonstrated that the tetragonal crystalline structure of KGeCl3 exhibited the least energy content, rendering it the most thermodynamically stable phase. It was found that the electronic band structure of KGeCl3 exhibited a direct band gap of 0.92 eV, thus positioning it as a material with promise for utilization as a photovoltaic absorber. Furthermore, the elastic properties of KGeCl3 were calculated, indicating the presence of suitable mechanical stability for practical applications. Additionally, the optical properties and thermoelectric performance of KGeCl3 were examined, thereby highlighting its potential for incorporation into thermoelectric devices. In summary, our research showcases how KGeCl3 holds significant promise as a viable substitute for lead-based perovskite materials in applications such as solar cells and other optoelectronic devices.

RESUMEN

Here, we report the synthesis and study of new orange-red (OR) colour-emitting phosphors Na2 ZnP2 O7 :xTb3+ (x = 1, 1.25, 1.5, and 1.75 mol%) using a conventional solid-state reaction. The sample crystallographic structures and their room temperature photoluminescence properties were measured using X-ray powder diffraction, excitation and emission spectra, as well as emission decay curves. X-ray diffraction analysis showed an isostructural tetragonal structure for all the doped materials with no impurities. Several colour emissions corresponding to 5 D4 →7 F6 (blue), 5 D4 →7 F5 (green), 5 D4 →7 F4 (orange) and 5 D4 →7 F3,2,0 (red) intraconfigurational transitions were observed and investigated. These colours were dominated by the OR colours. 5 D4 energy level lifetime was independent of Tb3+ concentration. Various radiative and luminescence parameters, such as experimental branching ratio, radiative decay rate, and luminescence quantum efficiencies, were calculated and discussed. Chromaticity diagram calculations illustrated an orange emission for all the studied materials.

Asunto(s)

Luminiscencia , Sustancias Luminiscentes , Color , Análisis Espectral , Difracción de Rayos X

RESUMEN

The fracture path follows grain boundaries (GB) in most metallic system under tensile test. In general, impurities, even in ppm concentration, that segregate to these boundaries can remarkably change materials mechanical properties. Predicting impurities segregation effects in Nickel super-alloys might not be seen as intuitive and perhaps more fundamental understanding is needed. We performed a density functional theory calculation to elucidate the effect of eight light elements (B, C, N, O, Al, Si, P and S) and twelve transition metal elements (Tc, Ti, V, Cr, Mn, Zr, Nb, Mo, Hf, Ta, W, Re) on Nickel ∑5(210) grain boundary formation and its Ni free surface. The effect of impurities was carefully examined by calculating different properties such as segregation, binding and cohesive energies, strengthening/embrittling potency and the theoretical tensile strength. Additionally, we employed the electron density differences and magnetic effects to explain why and how impurities such as B, S, V, Nb, Mn and W affect Nickel ∑5 GB. We used the generated data calculated on equal footing, to develop a fundamental understanding on impurity effect. A clear and strong correlation is found between difference in magnetic moment change between isolated and imbedded impurity atom on one hand and the tensile strength on the other hand. The higher the loss of the magnetic moment, the more the impurity consolidates the GB.