Lanthanide elements exhibit highly appealing spectroscopic properties that are extensively used for phosphor applications. Their luminescence contains precise information on the internal structure of the host materials. Especially, the polarization behavior of the transition sublevel peaks is a fingerprint of the crystal phase, symmetry, and defects. However, this unique feature is poorly explored in current research on lanthanide nanophosphors. We here report on a detailed investigation of the evolution of Eu3+ luminescence during the thermally induced phase transition of LaPO4 nanocrystal hosts. By means of c-axis-aligned nanocrystal assemblies, we demonstrate a dramatic change of the emission polarization feature corresponding to the distinct Eu3+ site symmetries in different LaPO4 polymorphs. We also show that changes of the nanocrystal structure can be identified by this spectroscopic method, with a much higher sensitivity than the X-ray diffraction analysis. This new insight into the nanostructure-luminescence relationship, associated with the unprecedented polarization characterizations, provides a new methodology to investigate phase transitions in nanomaterials. It also suggests a novel function of lanthanide emitters as orientation-sensing nanoprobes for innovative applications such as in bioimaging or microfluidics.

中文翻译：

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各向异性 LaPO4:Eu 纳米晶多晶型的偏振发光

镧系元素表现出极具吸引力的光谱特性，广泛用于荧光粉应用。它们的发光包含有关主体材料内部结构的精确信息。特别是，过渡亚能级峰的极化行为是晶相、对称性和缺陷的指纹。然而，目前对镧系元素纳米磷光体的研究很少探索这种独特的特征。我们在此报告了在 LaPO4 纳米晶体主体的热诱导相变过程中 Eu3+ 发光演变的详细研究。通过 c 轴排列的纳米晶体组件，我们展示了与不同 LaPO4 多晶型中不同 Eu3+ 位点对称性相对应的发射偏振特征的显着变化。我们还表明，这种光谱方法可以识别纳米晶体结构的变化，其灵敏度比 X 射线衍射分析高得多。这种对纳米结构-发光关系的新见解与前所未有的偏振表征相关，为研究纳米材料中的相变提供了一种新方法。它还表明镧系元素发射器作为方向感应纳米探针的新功能，用于创新应用，如生物成像或微流体。提供了一种研究纳米材料相变的新方法。它还表明镧系元素发射器作为方向感应纳米探针的新功能，用于创新应用，如生物成像或微流体。提供了一种研究纳米材料相变的新方法。它还表明镧系元素发射器作为方向感应纳米探针的新功能，用于创新应用，如生物成像或微流体。