2 research outputs found

    Effect of Covalence and Degree of Cation Order on the Luminous Efficacy of Mn<sup>4+</sup> Luminescence in the Double Perovskites, Ba<sub>2</sub><i>B</i>TaO<sub>6</sub> (<i>B</i> = Y, Lu, Sc)

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    The spectroscopic properties of the Mn4+ ion are investigated in the series of isostructural double perovskite compounds, Ba2BTaO6 (B = Y, Lu, Sc). A comparison of these properties highlights the influence of covalent bonding within the perovskite framework and the degree of order between the B3+–Ta cations on the energy and intensity of the Mn4+2E → 4A2 emission transition (R-line). These two parameters of the emission spectrum are of importance for practical application since they determine the phosphor luminous efficacy. The influence of covalent bonding within the corner shared BO6/2 and TaO6/2 perovskite framework on the energy of the R-line energy is investigated. From the spectroscopic data, we have derived information on the influence of the degree of order between the B3+ and Ta5+ cations on the intensity of the R-line. The lowest energy and the highest intensity of the R-line are found in the double perovskite, Ba2ScTaO6. The purpose of this work is to propose for first time an explanation of these effects in the considered double perovskites. The obtained results are useful guidelines for practical improvement and tuning of key parameters of phosphors to the desired values

    High Light Yield of Sr<sub>8</sub>(Si<sub>4</sub>O<sub>12</sub>)Cl<sub>8</sub>:Eu<sup>2+</sup> under X‑ray Excitation and Its Temperature-Dependent Luminescence Characteristics

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    In this work, we first investigate the relationship between temperature and lattice parameters by means of Rietveld refinement and then demonstrate its impact on the luminescence peak position of Eu<sup>2+</sup> in Sr<sub>8</sub>(Si<sub>4</sub>O<sub>12</sub>)­Cl<sub>8</sub>. It is found that with increases in temperature, lattice expansion takes place without significant distortion of the coordination around Eu<sup>2+</sup>. As a result, the crystal field splitting of the Eu<sup>2+</sup> 5d state decreases. At the same time, with the experimental data of the full width at half-maximum of Eu<sup>2+</sup> emission at different temperatures and the infrared spectrum, the effective phonon frequency is evaluated and the main vibration motions are determined using first-principles calculation. Due to the high light yield under X-ray excitation and the excellent thermal stability of luminescence intensity and decay, a further optimized sample Sr<sub>7.7</sub>Eu<sub>0.3</sub>(Si<sub>4</sub>O<sub>12</sub>)­Cl<sub>8</sub> could be a potential scintillation material
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