Rare-earth phosphors exhibit unique luminescence polarization features originating from the anisotropic symmetry of the emitter ion's chemical environment. However, to take advantage of this peculiar property, it is necessary to control and measure the ensemble orientation of the host particles with a high degree of precision. Here, we show a methodology to obtain the photoluminescence polarization of Eu-doped LaPO₄ nanorods assembled in an electrically modulated liquid-crystalline phase. We measure Eu³⁺ emission spectra for the three main optical configurations (σ, π and α, depending on the direction of observation and the polarization axes) and use them as a reference for the nanorod orientation analysis. Based on the fact that flowing nanorods tend to orient along the shear strain profile, we use this orientation analysis to measure the local shear rate in a flowing liquid. The potential of this approach is then demonstrated through tomographic imaging of the shear rate distribution in a microfluidic system.

中文翻译：

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监测稀土掺杂的纳米棒的方向，以进行流动剪切层析成像

稀土磷光体表现出独特的发光偏振特征，该特征源自发射极离子化学环境的各向异性对称性。然而，为了利用这种独特的性质，必须以高精度控制和测量主体颗粒的整体取向。在这里，我们展示了一种获得组装在电调制液晶相中的Eu掺杂LaPO ₄纳米棒的光致发光偏振的方法。我们测量三种主要光学结构（σ，π和α）的Eu ³⁺发射光谱，具体取决于观察方向和偏振轴），并将它们用作纳米棒取向分析的参考。基于流动的纳米棒趋向于沿着剪切应变分布取向的事实，我们使用这种取向分析来测量流动的液体中的局部剪切速率。然后，通过对微流体系统中的剪切速率分布进行层析成像，可以证明这种方法的潜力。