LumiLab, Department of Solid State Sciences, Ghent University, Krijgslaan 281-S1, Ghent, 9000, Belgium.
Phys Chem Chem Phys. 2013 Jun 14;15(22):8678-83. doi: 10.1039/c3cp44334e. Epub 2013 Apr 11.
Due to its bright yellow-to-red emission, europium doped Ca2SiS4 is a very interesting material for phosphor converted light emitting diodes. The emission spectrum is highly dependent on the Eu concentration and can consist of more than one emission band. We combined X-ray absorption fine structure and photoluminescence measurements to analyze the structure of europium centers in (Ca,Eu)2SiS4 luminescent powders. This paper provides an explanation for the concentration dependency of the emission spectra. We find that at low dopant concentrations a large fraction of trivalent europium ions is unexpectedly present in the powders. These trivalent europium ions tend to form defect clusters in the luminescent powders. Furthermore we observe a preferential substitution of the europium ions over the two different substitutional Ca sites, which changes upon increasing the dopant concentration. At high dopant concentration, the powder crystallizes in the monoclinic Eu2SiS4 structure. Once more a preferential substitution of the europium ions is observed. Summarizing, the influence of the concentration on the emission spectrum is explained by a difference in preferential occupation of the Eu ions in the lattice.
由于其亮黄色到红色的发射，铕掺杂的 Ca2SiS4 是用于荧光转换发光二极管的一种非常有趣的材料。发射光谱高度依赖于 Eu 浓度，并且可以包含多个发射带。我们结合了 X 射线吸收精细结构和光致发光测量来分析（Ca，Eu）2SiS4 发光粉末中铕中心的结构。本文对发射光谱的浓度依赖性提供了一个解释。我们发现，在低掺杂浓度下，出乎意料地有很大一部分三价铕离子存在于粉末中。这些三价铕离子在发光粉末中倾向于形成缺陷簇。此外，我们观察到 Eu 离子在两个不同取代的 Ca 位上的优先取代，随着掺杂浓度的增加而发生变化。在高掺杂浓度下，粉末结晶为单斜 Eu2SiS4 结构。再次观察到 Eu 离子的优先取代。总之，浓度对发射光谱的影响可以通过 Eu 离子在晶格中优先占据的差异来解释。
