Monitoring the orientation of rare-earth-doped nanorods for flow shear tomography

TL;DR

This paper presents a method to measure and image the orientation of rare-earth-doped nanorods in flow, enabling shear rate tomography in microfluidic systems using polarization-sensitive luminescence.

Contribution

It introduces a novel approach to determine nano rod orientation via photoluminescence polarization and applies it to shear rate imaging in microfluidics.

Findings

Successful measurement of Eu3+ emission spectra in different configurations

Demonstration of shear rate tomography in a microfluidic device

Potential for high-precision flow analysis using nanorod orientation

Abstract

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 nano rods assembled in an electrically modulated liquid-crystalline phase. We measure Eu3+ emission spectra for the three main optimal configurations ({\sigma}, {\pi} and {\alpha}, depending on the direction of observation and the polarization axes) and use them as a reference for the nano rod orientation analysis. Based on the fact that flowing nano rods 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.