Rare-earth doped nanocrystals possess optical transitions with significant either electric or magnetic dipole characters. They are of considerable interest for understanding and engineering light-matter interactions at the nanoscale with numerous applications in nanophotonics. Here, we study the ${}^5{D}_0{\to }^7{F}_1$ transition dipole vector in individual ${\mathrm{NaYF}}_4:{\mathrm{Eu}}^{3+}$ nanorod crystals by Fourier and confocal microscopies. A single-crystal host matrix leads to narrow emission lines at room temperature that permit separation of the 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 ${\mathrm{NaYF}}_4:{\mathrm{Eu}}^{3+}$ ensure well-defined electric or magnetic transitions, and are thus instrumental for probing locally their electromagnetic environment by standard confocal microscopy.

• Received 16 March 2020
• Revised 11 September 2020
• Accepted 5 October 2020

DOI:https://doi.org/10.1103/PhysRevApplied.14.054010