Photophysics and Dynamics of Surface Plasmon Polaritons-Mediated Energy Transfer in the Presence of an Applied Electric Field

Abstract

The possibility to transfer energy between molecular excitons across a metal film up to 150 nm thick represents a very attractive solution to control and improve the performances of thin optoeletronic devices. This process involves the presence of coupled surface plasmon polaritons (SPPs) at the two dielectric-metal interfaces, capable of mediating the interactions between donor and acceptor, located on opposite sides of the metal film. In this Article, the photophysics and the dynamics of an efficient SPP-mediated energy transfer between a suitable dye and a conjugated polymer is characterized by means of steady-state and time-resolved photoluminescence techniques. The process is studied in model multilayer structures (donor/metal/acceptor) as well as in electrically pumped heterostructures (donor/metal cathode/acceptor/anode), to verify the effects of applied electric fields on the efficiency and the dynamics of SPP-mediated energy transfer. A striking enhancement of the overall luminescence was recorded in a particular range of applied bias, suggesting the presence of cooperative effects between optical and electrical stimulations.

Cascaded plasmon-plasmon coupling mediated energy transfer across stratified metal-dielectric nanostructures

“…The key factor in an efficient nonradiative energy transfer is that the emission spectra of the donor should overlap the absorption spectra of the acceptor, hence several combinations of dyes have been studied in literature 14 17 32 33 ; the pair of Alq3, Tris (8-hydroxyquinolinato) aluminum and R6G, Rhodamine 6G is one the most efficient pair for our purpose. The absorption and emission spectra for the donor, the acceptor, and the spacer layers are depicted in Fig.…”

“…Notably, the method described in Equation (2) provides an accurate SP-NRET efficiency measurement as a result of its dependency on the donor emission in the presence of the acceptor (quenched donor PL intensity) and the acceptor emission in the presence of the donor (sensitized acceptor PL intensity) 4 . It is worth mentioning that the conventional methods for measuring NRET efficiency may not be essentially effective for multi-step ET process as they involve an extra correction factor definition due to the fact that these methods are mainly based on the ratio of the donor PL intensity quenching in the presence and the absence of the acceptor 14 17 . Therefore, taking into account both the donor and the acceptor PL intensities, the ET efficiency can be expressed through the quenched donor and the sensitized acceptor intensities method as…”

“…As a matter of fact, ET process gives rise to an additional nonradiative decay channel for the donor molecule that raises the overall decay rates and consequently reduces the donor lifetime. However, in the plasmonic nanostructures the modification of the donor lifetime should be interpreted differently as the presence of the acceptor molecule may not considerably modify the donor lifetime 14 17 . More specifically, in our structure the distance between the donor and the acceptor layers is large enough to prevent any direct nonradiative energy transfer from the donor dipole to the acceptor dipole and the modification of the donor decay rate occurs due to the ET from the excited donor molecule to the SP modes at the metal surface (the first step of SP-NRET).…”

“…As one can see in Equations (5 ) and ( 7 ), in which the normalized radiative decay rates of the dipole have been expressed for simple and stratified nanostructures, the integral limits varies from 0 to 1, while for the normalized nonradiative decay rate expression in Equations (6 ) and ( 8 ), the integral limits varies from 1 to ∞. This can be explained through the dipole behavior near the metal surface, which includes both, the far (0 < u < 1) and evanescent fields ( u > 1), the corresponding region can be independently defined versus u to cover either the real (0 < u < 1) or complex ( u > 1) angles of incidence 3 17 .…”

“…Since the very first study on SP-NRET through optically thick/lossy metal films 14 , several applicable systems have been verified to enhance the efficiency of the process and extend the effective ET range 2 5 15 16 . Despite the fact that SP improves the ET range up to 150 nm through a silver film 17 , the mechanism suffers from the significant energy loss due to the absorption by thick metal film.…”