Mapping and Quantifying Electric and Magnetic Dipole Luminescence at the Nanoscale

We report on an experimental technique to quantify the relative importance of electric and magnetic dipole luminescence from a single nanosource in structured environments. By attaching a ${\mathrm{Eu}}^{3+}$-doped nanocrystal to a near-field scanning optical microscope tip, we map the branching ratios associated with two electric dipole and one magnetic dipole transitions in three dimensions on a gold stripe. The relative weights of the electric and magnetic radiative local density of states can be recovered quantitatively, based on a multilevel model. This paves the way towards the full electric and magnetic characterization of nanostructures for the control of single emitter luminescence.

Figure 1

(a) Experimental setup. Inset: scanning electron microscope image of the ${\mathrm{Eu}}^{3+}$-doped nanocrystal attached to the tungstene NSOM tip. The nanocrystal is approximately 200 nm large. (b) Luminescence spectra of the ${\mathrm{Eu}}^{3+}$-doped KYF nanocrystal at several distances from a gold mirror.

Figure 2

(a) Band diagram of the ${\mathrm{Eu}}^{3+}$ ions. (b) Branching ratios associated with transitions 1 (blue), 2 (red), and 3 (green) as a function of the distance to a gold mirror. Full lines: analytical expressions; circles: experimental values.

Figure 3

(a) From left to right: topography of the gold stripe; branching ratios of transitions 1, 2, and 3 in the $x$-$y$ plane. Image size is $3\times 4.8\mu {\mathrm{m}}^2$. (b) From left to right: branching ratios of transitions 1, 2, and 3 in the $y$-$z$ plane. Image size is $4\times 1\mu {\mathrm{m}}^2$.

Figure 4

(a) Three-level model of ${\mathrm{Eu}}^{3+}$ ions. (b) Relative radiative LDOS versus the distance to a gold mirror. Full line: analytical formulas; red dots: experimental relative electric radiative LDOS; blue circles: experimental relative magnetic radiative LDOS.