Steudel Franziska, Johnson Jacqueline A, Johnson Charles E, Schweizer Stefan
Fraunhofer Application Center for Inorganic Phosphors, Branch Lab of Fraunhofer Institute for Microstructure of Materials and Systems IMWS, Lübecker Ring 2, 59494 Soest, Germany.
University of Tennessee Space Institute, Tullahoma, TN 37388, USA.
Materials (Basel). 2018 May 17;11(5):828. doi: 10.3390/ma11050828.
The application of Mössbauer spectroscopy to luminescent materials is described. Many solids doped with europium are luminescent, i.e., when irradiated with light they emit light of a longer wavelength. These materials therefore have practical applications in tuning the light output of devices like light emitting diodes. The optical properties are very different for the two possible valence states Eu 2 + and Eu 3 + , the former producing ultraviolet/visible light that shifts from violet to red depending on the host and the latter red light, so it is important to have a knowledge of their behavior in a sample environment. Photoluminescence spectra cannot give a quantitative analysis of Eu 2 + and Eu 3 + ions. Mössbauer spectroscopy, however, is more powerful and gives a separate spectrum for each oxidation state enabling the relative amount present to be estimated. The oxidation state can be identified from its isomer shift which is between - 12 and - 15 mm/s for Eu 2 + compared to around 0 mm/s for Eu 3 + . Furthermore, within each oxidation state, there are changes depending on the ligands attached to the europium: the shift is more positive for increased covalency of the bonding ligand X, or Eu concentration, and decreases for increasing Eu⁻X bond length.
描述了穆斯堡尔光谱在发光材料中的应用。许多掺杂铕的固体具有发光性，即当用光照时，它们会发射波长更长的光。因此，这些材料在调节发光二极管等器件的光输出方面具有实际应用。对于两种可能的价态Eu²⁺和Eu³⁺，其光学性质有很大不同，前者产生紫外/可见光，根据基质的不同从紫色变为红色，后者产生红光，所以了解它们在样品环境中的行为很重要。光致发光光谱无法对Eu²⁺和Eu³⁺离子进行定量分析。然而，穆斯堡尔光谱更强大，能为每种氧化态给出单独的光谱，从而可以估计每种氧化态的相对含量。氧化态可通过其同质异能位移来识别，Eu²⁺的同质异能位移在-12至-15毫米/秒之间，而Eu³⁺的约为0毫米/秒。此外，在每种氧化态内，会因与铕相连的配体不同而发生变化：随着键合配体X的共价性增加或铕浓度增加，位移更正，而随着Eu-X键长增加，位移减小。
