Joos Jonas J, Seijo Luis, Barandiarán Zoila
LumiLab, Department of Solid State Sciences, and Center for Nano- and Biophotonics (NB-Photonics) , Ghent University , 9000 Ghent , Belgium.
Departamento de Química, Instituto Universitario de Ciencia de Materiales Nicolás Cabrera, and Condensed Matter Physics Center (IFIMAC) , Universidad Autónoma de Madrid , 28049 Madrid , Spain.
J Phys Chem Lett. 2019 Apr 4;10(7):1581-1586. doi: 10.1021/acs.jpclett.9b00342. Epub 2019 Mar 21.
Direct evidence is given for the existence of intervalence charge transfer (IVCT) states of Eu/Eu pairs in Eu-doped CaF, SrF, and BaF. They are detected in diffuse reflectance spectra. In doped materials, IVCT states, in which an electron transfer occurs between two metal sites differing only in oxidation state, are rather difficult to observe because the absorption bands are extremely broad and flat, their intensity is low, and no emission follows the IVCT absorptions. Their assignment as IVCT states is provided by state-of-the-art multiconfigurational ab initio calculations. Although IVCT states of lanthanide-doped materials have largely been overlooked so far, they can cause luminescence quenching and even complete luminescence excitation loss. Their direct observation and independent assignment in classical dopant (Eu) and hosts (CaF, SrF, BaF) are very significant: They suggest that the occurrence of IVCT states in other lanthanide-activated materials is very likely overlooked and their impact is ignored.
在掺铕的CaF、SrF和BaF中，直接证明了Eu/Eu对的价间电荷转移（IVCT）态的存在。它们在漫反射光谱中被检测到。在掺杂材料中，IVCT态是指电子在仅氧化态不同的两个金属位点之间发生转移的状态，由于吸收带极其宽且平坦、强度低，并且IVCT吸收之后没有发射，所以很难观察到。通过最先进的多组态从头算计算确定了它们为IVCT态。尽管到目前为止，镧系掺杂材料的IVCT态在很大程度上被忽视了，但它们会导致发光猝灭甚至完全失去发光激发。在经典掺杂剂（Eu）和主体（CaF、SrF、BaF）中对它们的直接观察和独立确定非常重要：这表明其他镧系激活材料中IVCT态的出现很可能被忽视，其影响也被忽略了。
