Measuring the magnetic dipole transition of single nanorods by spectroscopy and Fourier microscopy

TL;DR

This study investigates the magnetic dipole transition in individual Eu-doped nanorods using spectroscopy and Fourier microscopy, revealing a fully magnetic transition with consistent dipole orientation, advancing nanophotonics understanding.

Contribution

It provides the first detailed measurement of the magnetic dipole transition vector in single nanorods, demonstrating narrow emission lines and stable dipole orientations at room temperature.

Findings

Confirmed a fully magnetic transition in single nanorods.

Observed low variability in dipole orientation across nanorods.

Estimated the proportion of Stark sublevel transitions.

Abstract

Rare-earth doped nanocrystals possess optical transitions with significant either electric or magnetic dipole characters. They are of strong interest for understanding and engineering light-matter interactions at the nanoscale with numerous applications in nanophotonics. Here, we study the $^5$D$_0\rightarrow ^7$F$_1$ transition dipole vector in individual NaYF$_4$:Eu$^{3+}$ nanorod crystals by Fourier and confocal microscopies. {Single crystalline host matrix leads to narrow emission lines at room temperature that permit to separate Stark sublevels resulting from the crystal field splitting}. We observe a fully magnetic transition and {low variability} of the transition dipole orientation over several single nanorods. We estimate the proportion of the dipole transitions for the Stark sublevels. We also determine an effective altitude of the rod with respect to the substrate. The narrow emission lines characteristic of NaYF$_4$:Eu$^{3+}$ ensure well-defined electric or magnetic transitions, and are thus instrumental for probing locally their electromagnetic environment by standard confocal microscopy.