Spectral Tuning by Selective Enhancement of Electric and Magnetic Dipole Emission

Abstract

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.

Purcell factor of spherical Mie resonators

“…However, interest in magnetic spontaneous emission has been growing over the last years, in particular using trivalent lanthanide ions [37][38][39]. This strong interest in coupling lanthanide ions to nano-cavities makes us emphasize the fact that both electric and magnetic emitters can give rise to an enhanced spontaneous decay rate.…”

Identifying diamagnetic interactions in scattering and nonlinear optics

“…In consequence, higher-order couplings expressed in multipolar form, such as the light-matter interactions mediated by a magnetic dipole, can usually be disregarded. However, these higher-order terms are important for certain systems, such as chiral discrimination in molecules of low symmetry [1,2], light-harvesting complexes [3], nanomaterials [4][5][6], metamaterials [7,8] and numerous theoretical studies including optical trapping [9][10][11][12][13][14]. Such terms also assume greater significance for systems in which electric-dipole couplings are either very small or vanish altogether-when, for example, a relevant electronic transition is electric-dipole forbidden by symmetry.…”

Excitation of Magnetic Dipole Transitions at Optical Frequencies

“…Depending on whether the excitation wavelength is tuned into resonance with a MD or ED transition, an Eu 3þ nanoparticle will map out the distribution of the magnetic or the electric field. At 532.0 nm excitation wavelength, the Eu 3þ exhibits an ED transition corresponding to one of the 7 [see Fig. 1(a)] [21], and hence an image taken with an azimuthally polarized beam tuned to 532.0 nm yields a doughnut-shaped intensity distribution with a characteristic minimum in the center, as shown in Fig.…”

“…The detected signal arises from a combination of ED and MD transitions at lower energy than the excitation, primarily the 5 D 0 → 7 F 2 and 5 D 0 → 7 F 1 transitions in the spectral range of 603-635 and 580-603 nm, respectively [see Fig. 1(a)] [7,29]. For a plane wave in free space the magnetic field strength is related to the electric field strength by the speed of light (B ¼ E=c).…”

“…Nature, however, also provides materials with strong MD transitions, namely, rare earth ions. Many of their MD transitions are found within the visible spectrum, making them promising candidates for the optical excitation of MD transitions.Much theoretical and experimental work has been done exploring the MD and ED contributions to spontaneous emission from Eu 3þ and other trivalent rare earth ions [1,[7][8][9][10]. Lifetimes and oscillator strengths have been studied as a function of local environment [11][12][13][14], ion concentration [15][16][17], and particle size [18][19][20][21][22][23].…”