Effects of sample thickness on the optical properties of surface plasmon-coupled emission

In recent reports, we demonstrated coupling of excited fluorophores with thin silver or gold films resulting in directional surface plasmon-coupled emission (SPCE) through the silver film and into the glass substrate. In the present report, we describe the spectral and spatial properties of SPCE from sulforhomamine 101 in polyvinyl alcohol (PVA) films of various thicknesses on 50-nm silver films. The PVA thickness varied from about 30 to 750 nm. In thin PVA films with a thickness less than 160 nm, SPCE occurred at a single angle in the glass substrate and displayed only p polarization. As the PVA thickness increased to 300 nm, we observed SPCE at two angles, with different s or p polarization for each angle. For PVA films from 500 to 750 nm thick, we observed SPCE at three or four angles, with alternating s and p polarizations. The multiple rings of SPCE and the unusual s-polarized emission are consistent with the expected waveguide modes in the silver-PVA composite film. However, in contrast to our expectations, the average lifetimes of SPCE were not substantially changed from the PVA films. The observation of SPCE at multiple angles and with different polarization opens new opportunities for the use of SPCE to study anisotropic systems or to develop unique sensing devices.