Plasmonic enhancement of electroluminescence

Abstract

Here plasmonic effect specifically on electroluminescence (EL) is studied in terms of radiative and nonradiative decay rates for a dipole near a metal spherical nanoparticle (NP). Contribution from scattering is taken into account and is shown to play a decisive role in EL enhancement owing to pronounced size-dependent radiative decay enhancement and weak size effect on non-radiative counterpart. Unlike photoluminescence where local incident field factor mainly determines the enhancement possibility and level, EL enhancement is only possible by means of quantum yield rise, EL enhancement being feasible only for an intrinsic quantum yield Q0 < 1. The resulting plasmonic effect is independent of intrinsic emitter lifetime but is exclusively defined by the value of Q0, emission spectrum, NP diameter and emitter-metal spacing. For 0.1< Q0 < 0.25, Ag nanoparticles are shown to enhance LED/OLED intensity by several times over the whole visible whereas Au particles feature lower effect within the red-orange range only. Independently of positive effect on quantum yield, metal nanoparticles embedded in an electroluminescent device will improve its efficiency at high currents owing to enhanced overall recombination rate which will diminish manifestation of Auger processes. The latter are believed to be responsible for the known undesirable efficiency droop in semiconductor commercial quantum well based LEDs at higher current. For the same reason plasmonics can diminish quantum dot photodegradation from Auger process induced non-radiative recombination and photoionization thus opening a way to avoid negative Auger effects in emerging colloidal semiconductor LEDs.

Possible nanoantenna control of chlorophyll dynamics for bioinspired photovoltaics

“…We consider the simplest case of a single solid spherical nanobody as a nanoantenna to control the excited state decay rate. The calculation scheme has been described elsewhere 21,63 . The radiative γ rad and the total γ tot decay rates for an emitter can be calculated asfor the emitter dipole moment oriented perpendicular (normally) to the sphere surface, denoted by the ‘P’ subscript, andfor the emitter dipole moment oriented tangentially (i.e.…”

“…However, similar to radiophysical antennas, proximity of a metal body offers an option to substantially increase the intrinsic efficiency of an emitter with considerable internal losses, i. e., in the optical language, with Q ≪ 1. This may result in the overall photoluminescence intensity enhancement over several orders of the magnitude for poor emitters 20 and, what is extremely essential in optoelectronics, even in enhancement of the efficiency of electrically pumped light-emitting devices, semiconductor LEDs or organic ones, OLEDs, where making use of the incident intensity enhancement is not the case at all 21,22 .…”

Colloidal Photoluminescent Refractive Index Nanosensor Using Plasmonic Effects

“…The calculation scheme and the relevant equation can be found in Ref. [14,16]. There are three basic processes affecting luminescence intensity.…”

“…For perfect emitters with the intrinsic quantum yield Q 0 = 1, a metal body will necessarily promote quenching with Q(r) < Q 0 . However, for emitters with low Q 0 < 1, quenching may not be pronounced and even Q(r) > Q 0 can be obtained [16]. Generally, in simple colloidal metal structures with a few nm dielectric spacers (oxide shells, polyelectrolytes, Langmuir -Blodgett films) perfect emitters show enhancement up to 10 times whereas poor emitters show enhancement factors rising inversely proportional to Q 0 , i.e.…”

“…More detail on the calculation scheme and explicit equations for the parametrs involved can be retrieved in Refs. [14,16]. Figure 2 shows a set of the extinction spectra for Ag spheres to recall the primary shift of extinction spectra with familiar 200 nm/RIU sensitivity.…”