Spectral tuning by selective enhancement of electric and magnetic dipole emission.

We demonstrate that magnetic dipole transitions provide an additional degree of freedom for engineering emission spectra. Without the need for a high-quality optical cavity, we show how a simple gold mirror can strongly tune the emission of trivalent europium. We exploit the differing field symmetries of electric and magnetic dipoles to selectively direct the majority of emission through each of three major transitions (centered at 590, 620, and 700 nm), and present a model that accurately predicts this tuning from the local electric and magnetic density of optical states.