Rudolph Erasmus

A series of MgTa2O6: 1mol % Cr3+, x mol% Si4+ (x = 2, 4, 6, 8, 10, and 12) was synthesised by a solid-state chemical reaction route at 800 ⁰C for 8 hours, after ball milling the mixed precursors. X-ray diffraction (XRD) showed a pure phase and crystalline particles of MgTa2O6: 1 mol% Cr3+, x mol% Si4+, even in the presence of the co-dopant ions. The band gap of the material was approximated to be 4.37 ± 0.19 eV from the Tauc Plot. The photoluminescence (PL) emission spectrum displayed a broad band between 700 and 1000 nm, which is in the near infrared (NIR), with a barycentre at 825 nm, when the sample was excited at 280 nm. The emission originates from the spin-allowed transition of Cr3+ ions (4T2 - 4A2). The experimental results showed that the optimal Si4+ concentration not only increased the material's emission intensity and luminescence lifetime but also the quantity of defects inside the material. The time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis confirmed the presence of all expected ions. Finally, thermoluminescence (TL) measurements were employed for a better understanding of the kinetic mechanism and investigation of the electron trapping centres (ETC) in this material. Trap depths were found from 0.76 ± 0.01 to 1.45 ± 0.06 eV using different methods. The experimental results presented in this study demonstrate that this material is promising for display technologies, security marking, and the possible future development of persistent luminescence (PersL) applications.

This paper presents a study of gamma irradiation effects on the optical and scintillation properties of pure and yttrium-doped BaF ₂ crystals with yttrium concentrations of 1, 3, and 5 mol%. The optical transmittance, light output, and energy resolution of twenty-four 1×1×1 cm ³ samples were measured before and after ⁶⁰ Co gamma irradiation, with absorbed doses up to 3.56 Mrad. In pure BaF ₂ samples, no noticeable degradation in scintillation properties was observed with increasing absorbed dose. In yttrium-doped samples, a deterioration of scintillation properties is observed, with the fast component of crystal luminescence deteriorating more than the slow one. The correlation between the loss of light output and the radiation-induced decrease of optical transmittance, together with the absence of structural changes in Raman spectra, indicates that the degradation of scintillation properties is primarily due to increased self-absorption, rather than to disruption of the scintillation mechanism.

Dopant fluence on the physicochemical and conductivity properties of carbon spheres.

Four polymorphs of the ternary molecular salt cocrystal complex (3-hydroxypyridinium)·(9-anthracenecarboxylate)·(trinitrobenzene) were isolated. In all four polymorphs proton transfer occurred from the carboxylic acid to the nitrogen atom of the pyridine ring to form ternary molecular salts. Form I crystallizes as orange needles/rods, form II crystallizes as red blocks, and forms III and IV both crystallize as orangey-yellow needles. Differential scanning calorimetry indicates that form II is the thermodynamically most stable form, further supported by energy lattices calculated within periodic boundary conditions. Quantum theory of atoms in molecules (QTAIM) analysis revealed strong hydrogen bonds and charge-transfer interactions, with notable variations in the strength of these interactions across the polymorphs. Polymorph I showed the strongest charge-assisted O–H⋯O hydrogen bonds, while polymorph II displayed the most significant π⋯π interactions. Photoluminescence and UV-vis studies showed that the polymorphs exhibit differing band gaps, correlating with their observed colours and electronic structures. These results emphasize the role of polymorphism in modulating the physical and chemical properties of multi-component molecular crystals.

Ten hybrid metal halide perovskites containing divalent dabconium cations and alkali-metal ions have been structurally characterised and their band gaps determined, with six new crystal structures reported. Five compounds of the formula (C₆H₁₄N₂)[BX₃], where B = Na⁺ and X = Cl^- or Br^-, B = K⁺ and X = Cl^- or Br^- and B = Cs⁺ and X = I^-, were found to exhibit one-dimensional (1D) hexagonal perovskite structures containing face-sharing metal halide octahedra that form 1D inorganic polymers. Five compounds of the formula (C₆H₁₄N₂)[BX₃] , where B = K⁺ and X = Br^- or I^-, and B = Cs⁺ and X = Cl^-, Br^- or a mixture of Cl^- and I^-, display three-dimensional (3D) parent perovskite structures containing corner sharing metal halide octahedra that form a 3D framework. A correlation was found between the formation of a 1D or 3D perovskite structure and the sum of ionic radii of the metal and halide ions. The band gaps of the compounds fall in the range 3.42 eV to 5.33 eV. It was found that a 3D perovskite has a smaller band gap than a 1D perovskite, while the halide ion also affects the band gap.