Mechanism of enhanced light emission from an emitting layer embedded in metal-insulator-metal structures

Photoluminescence spectra of a dye layer placed at the middle of a metal-insulator-metal (MIM) structure are measured and compared with those of a reference sample without metallic layers. The observed spectra are much sharper than those of the reference sample and the peak wavelength shifts to shorter wavelengths as the observation angle increases. Furthermore, the enhancement in both the emission intensity and power is clearly observed. Electromagnetic calculations based on a point dipole model indicate that the observed light emission is mediated by radiative surface-plasmon polaritons and lowest-order transverse electric modes supported by the MIM structure. The observed enhancement is thought to result from a combination of the enhanced spontaneous emission rate and concentration of radiation intensities in a relatively narrow wavelength region brought by the MIM structure.