Nonradiative energy transfer from atoms to surface plasmons

Luminescent molecules near metal surfaces can have dramatically decreased quantum efficiencies and lifetimes. For example, decreases of approx. 104 in quantum efficiency and in lifetime occur for nitrogen atoms within 3 nm of potassium surfaces. This thesis presents experimental decay curves for light emission from N atoms in an N2 matrix of varying thickness (3 to 1000 nm) on sapphire, silver, sodium and potassium substrates. Theoretical decay curves are derived and found to be in agreement with the experimental curves. Both experiment and theory agree that for thick potassium films there is near resonant coupling between excited nitrogen atoms and potassium surface plasmons. For metal films, both film thickness and surface roughness affect the decay curves. The degree of nonradiative coupling of N atoms to a nearby metal surface was modeled by a modified form of classical theory describing the interaction of an oscillating electric dipole with a partially reflecting and partially absorbing dielectric interface. This interaction between the dipole and surface is dominated by energy transfer to surface plasmons (surface electron density oscillations) when the dipole is very close to the surface. If the emission energy of the dipole is nearly identical to the surface plasmon resonance energy, then coupling between the dipole and surface can be very strong. The surface plasmon resonance energy is dependent on bulk metal dielectric constants (which depend on electron density and damping within the metal), metal film thickness (due to interactions of surface plasmons on both sides of a thin metal film) and dieletric constants of the surrounding environment