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Lanthanide-doped β-Ca2SiO4 has been regarded as a promising material for use in light-emitting diode (LED) phosphors. Nevertheless, the performance of these luminescent materials activated by lanthanide ions depends strongly on the host matrix. The challenge lies in controlling the phase under ambient conditions in a material that exists in five polymorphic forms. Herein, we report the synthesis of β-Ca2SiO4 containing Ce and Eu ions via the Sol–Gel method. The pure and doped samples were characterized using thermogravimetric (TG) and differential thermal (DT) analysis, X-ray diffraction (XRD) and Rietveld–XRD analysis, scanning electron microscopy (SEM), X-ray absorption near edge structure (XANES), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and defect calculations. XRD analyses show the predominant formation of the β-phase. Morphological analyses by SEM show smaller particle sizes in Ce- and Eu-doped β-Ca2SiO4 than pure samples. This result suggests that Ce3+ is more efficient at stabilizing the β-Ca2SiO4 polymorph. The PL emission of the β-Ca2SiO4:Eu, excited at 393 nm, provides evidence about the existence of two nonequivalent sites, with one of them evolving to a high symmetry site and the other one remaining in a low symmetry. PL results are corroborated by defect calculations in which it is evident that both Eu3+ and Ce3+ ions prefer to be incorporated into the two Ca2 sites compensated by a Ca1 vacancy, including a probable change in the coordination number of the Eu3+ ion. The abrupt distortion of one of the Eu3+ sites is accompanied by the high 5D0 → 7F4 transition. Also, we present XANES and XPS analyses combined with defect calculations for Eu2+ and Ce4+ ions to discuss the likely coexistence of valency states in the host matrix. Lastly, the results offer insights into improving the performance of phosphor-converted white LEDs. [ABSTRACT FROM AUTHOR]

Magnesium tetraborate (MgB4O7) is an example of a material that has attracted the attention of researchers in the field of ionising radiation dosimetry. Several challenges are present in order to achieve considerable advances in luminescence dosimetry. The incorporation of efficient dopants in the host matrix has been an experimentally useful but limited strategy. The lack of specific information about the introduced defects as well as their connection with the trapping and recombination processes associated with light emission may be quoted as challenging examples. Here, we demonstrate the influence of lithium incorporation on Optically Stimulated Luminescence (OSL)/Thermoluminescence (TL) signal modification/suppression of MgB4O7 by combining experimental and computational procedures. Li substitution into the Mg site leads to a signal suppression due to the probable quenching of the Fs and Fs+ centres in MgO and the formation of O′′i, drastically reducing the possibility of MgO anti-Schottky defect formation in MgB4O7. When using Li-co-doped MgB4O7:Ce3+, the Li ions act as a charge balancer, facilitating the entry of Ce ions into the interstitial pores and making possible a positive synergistic effect on the luminescence and dosimetric properties. These findings provide new insights into designing more efficient dosimeters by tuning dopants. [ABSTRACT FROM AUTHOR]

MgB4O7 has attracted much attention for dosimetric applications in recent years, for reasons including its low effective atomic number and large bandgap to accommodate charge carrier traps. Particularly, the charge carrier traps in undoped MgB4O7 may be associated with natural defects in the host matrix, generated during the synthesis processes or even during post-synthesis treatment. Their elucidation is the key to controlling point defects in the host matrix and obtaining desirable dosimetric characteristics. In this context, we have estimated the intrinsic defect formation energy and its creation mechanism using the Mott–Littleton method. For this, we developed a new set of potential parameters based on the Buckingham and Morse potentials. The potential parameters were validated and used to obtain the structural, mechanical, and dielectric properties. Also, we connected these intrinsic defects with charge carrier traps for understanding the origin of optically stimulated luminescence (OSL) of the undoped material. The theoretical OSL decay pattern was obtained using a set of rate parameters. The results provide new insights into the control of defects and pave the way for discussing features of the doped material. [ABSTRACT FROM AUTHOR]

Structural, mechanical, elastic, and dielectric properties of the AMgF3 (A = K, Rb, and Cs) compounds were investigated using classical atomistic simulation. A new set of interatomic potentials was developed for these compounds. Lattice parameters and interatomic distances have shown to accurately reproduce all structures, with very close agreement to the experimental data. In all cases, the relative error is below 0.5%. Effect of hydrostatic pressure in the structural, mechanical, elastic, and dielectric properties of these materials were studied from 0 up to 50 GPa. Compounds behavior and stability under pressure were analyzed. KMgF3 and RbMgF3 changed from brittle to ductile at approximately 2 GPa. These calculations play an important role in understanding the properties of the AMgF3 (A = K, Rb, and Cs) compounds under pressure, and open up a new opportunity to study defects in this class of materials. © 2019 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]