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First-principle calculations were used to investigate the structural, optoelectronic, elastic and thermodynamic properties of Br-doped CsPbI3 perovskite material using GGA-PBE, SCAN, and LDA functionals. The computed lattice parameters are consistent with the experimental and theoretical calculations, reported in the literature. The band structure along with the electronic density of states indicated that CsPbI3-xBrx (x = 0, 1, 2, 3) materials are semiconductors with direct band gaps, as projected using the three functionals. The energy band gap of CsPbI3 was tuned by replacing I ions with Br ions, resulting in CsPbI2Br, CsPbBr2I, and CsPbBr3 materials. These perovskite materials were found to be mechanically stable, ductile in nature and elastically anisotropic. The results of optical parameters such as absorption coefficients, refractive index, optical conductivity, optical reflectivity, electron energy loss, and extinction coefficients were calculated and analysed. The thermodynamic parameters including heat capacity, and Debye temperature were calculated. The direct band gap and energy-dependent optical parameters especially the absorption coefficient in the infrared and visible region of these perovskites’ materials suggest that they might be candidates for potential use in photovoltaic solar cells and optoelectronic applications.

The impact of Na atom deintercalation on olivine NaMnPO4 was investigated in a first-principle study for prospective use as cathode materials in Na-ion batteries. Within the generalized gradient approximation functional with Hubbard (U) correction, we used the plane-wave pseudopotential approach. The calculated equilibrium lattice constants are within 5% of the experimental data. The difference in equilibrium cell volumes for all deintercalated phases was only 6%, showing that NaMPO4 is structurally more stable. The predicted voltage window was found to be between 3.997 and 3.848 V. The Na1MnPO4 and MnPO4 structures are likely to be semiconductors, but the Na0.75MnPO4, Na0.5MnPO4, and Na0.25MnPO4 structures are likely to be metallic. Furthermore, all independent elastic constants for NaxMPO4 structures were shown to meet the mechanical stability requirement of the orthorhombic lattice system.

Researchers are in active pursuit of scintillator materials for diagnostic applications in medical science. Such pursuits are only achieved through experimental investigations of phosphor materials. To address this issue, we focused on the comparative photoluminescent behaviours of inorganic orthophosphates, NaMPO 4 :xCe 3+ (M = Ca, Ba, Sr, Mg), synthesized via the traditional solid-state reaction method and the combustion method. The combustion method is a simple and rapid method of producing a variety of nanosized particles (use of nitrates, fuels, etc.), while the solid-state reaction method (use of metal oxides) focus on a gradual heating of the powders from room temperature to 900 °C (to allow for interdiffusion of cations). Various techniques such as XRD, SEM and PL were used to characterize these phosphor materials. Further, the CIE (Commission international de Iéclairage) plots were then obtained using the PL data to compare colour tuning in each case. A comparison of the results reveals that the NaBaPO 4 :xCe 3+ phosphor displayed the best photoluminescence behaviour for an optimal concentration of x = 0.5 mol % using the combustion method of synthesis, on the other hand using the solid-state reaction method, the best photoluminescence was obtained for an optimal concentration of x = 1 mol % for the same material. In each of the above cases, the PL emission spectra was due to the 5d→ 4f transition of the Ce 3+ ions. The results points to the fact the Ce 3+ emissions in the NaBaPO 4 :xCe 3+ ion occurs for a higher concentration in the solid-state method and for a lower concentration in the combustion method scenario (quenched for same concentration in the combustion method). This could be attributed to the slow diffusion of ions in the solid-state reaction method, compared to the fast combustion in the combustion method (600 °C).

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