Europium luminescence enhancement induced by a resonant mode in a waveguide of planar metallic walls

We report the experimental results of emission from europium ions inside a planar waveguide. The waveguide is constituted by a MgF₂:Eu ²⁺ film between Al metallic walls, with a film thickness appropriate to support a guided mode with wavelength inside of the excitation spectrum of the Eu ions. A guided mode is produced by incident light through a thin metallic film at an angle of incidence such that its wave vector component parallel to the waveguide couples resonantly to the mode. The luminescence of Eu ²⁺ in the waveguide of polycrystalline MgF₂ was found to have a maximum at 440 nm. This emission was ascribed to electronic transitions of Eu²⁺ ions dipoles on a lattice of MgF₂. For an excitation light of 360 nm, the integrated emission versus angle of incidence showed a maximum for an incident light angle of 20°. This behavior is explained because of the excitation light, for those wavelength and angle of incidence, couple to a mode along the waveguide and more emitters are excited in the optical path of the guided light.