Beschreibung:
<jats:title>Abstract</jats:title><jats:p>In this study, the effect of host cations on the local structure around the dopant site of materials from the xenotime family is systematically studied on the molecular level. A series of six Eu<jats:sup>3+</jats:sup>‐doped xenotime‐type single crystals (Tb, Y, Ho, Er, Yb, and LuPO<jats:sub>4</jats:sub>) have been grown and spectroscopically analyzed by using polarization‐dependent laser‐induced luminescence spectroscopy (p‐TRLFS). Our results demonstrate that the structural disorder changes in a non‐linear manner with a structural break between Yb<jats:sup>3+</jats:sup> and Lu<jats:sup>3+</jats:sup>. Despite adopting identical crystal structures, the solid solutions of these materials vary significantly, and differ from monazite solid solutions. Similar Eu<jats:sup>3+</jats:sup> incorporation behavior with a strongly distorted dopant site is found for the early members of the xenotime family, whereas LuPO<jats:sub>4</jats:sub> with the largest host versus dopant radii mismatch is anomalous in that it contains the most symmetrical lattice site. This goes along with a significantly stronger crystal field, indicating a shorter Eu−O bond length, as well as a strong vibronic coupling to external translational lattice vibrations. The p‐TRLFS analysis confirms the breakdown of the crystallographic site symmetry from <jats:italic>D</jats:italic><jats:sub>2<jats:italic>d</jats:italic></jats:sub> to <jats:italic>C</jats:italic><jats:sub>1</jats:sub> in YPO<jats:sub>4</jats:sub>, whereas a small distortion of the crystallographic site in LuPO<jats:sub>4</jats:sub> results in an <jats:italic>S</jats:italic><jats:sub>4</jats:sub> point symmetry for the Eu<jats:sup>3+</jats:sup> cation. The lattice with the smallest cation host site is no longer sufficiently flexible to make room for Eu<jats:sup>3+</jats:sup> and instead “forces” the guest ion to occupy a less distorted Lu<jats:sup>3+</jats:sup> site.</jats:p>