Self‐Modulated White Light Outcoupling in Doped Organic Nanowire Waveguides via the Fluctuations of Singlet and Triplet Excitons During Propagation

Abstract

polymers, [ 5 ] and small organic molecules [ 6–11 ] are widely investigated for their applications in optoelectronic communications and sensors. [ 12 , 13 ] The semiconductor and metal waveguides are based on the propagation of photons and surface plasmon polaritons (SPPs), respectively. Very recently, it was proposed that organic waveguide materials work with a distinct principle, i.e., exciton polaritons (EPs) formed by the strong coupling between Frenkel excitons and photons play an essential role in organic optical waveguides. [ 14 ] Due to the photon–exciton coupling, EPs show excellent propagation properties compared with uncoupled light. [ 15 ] Moreover, the participation of excitons might introduce interesting electron and energy processes during propagation, which are helpful for the realization of novel waveguide behaviors. Excitons can be converted between two organic compounds accompanied by energy transfers, through which white light emissions (WLEs) can be achieved. [ 16 ] As devices are being designed on ever diminishing scales, WLE sub-wavelength waveguides are desired as small white light generators in micro-photonic circuits. In general, white lights are generated by the incomplete quenching of donor emissions and the color mixing of donors and acceptors at given doping ratios by either singlet–singlet (SSET), [ 17 ] or triplet–triplet energy transfer (TTET). [ 18 ] However, this strategy is greatly limited in constructing single nanowire WLE waveguides in that the color is supersensitive to the doping ratio, and a slight change of acceptor content by environmental heating, oxidation, or light irradiation in practical applications will signifi cantly infl uence the white light output. [ 19 ] Inspired by the voltage stabilizer in electric circuits, herein we demonstrate a kind of optical modulator based on doped organic nanowire waveguides, which can output constant white light from the wire terminus, despite the doping contents. The modulation was realized by the fl uctuations of singlet and triplet excitons during EP propagation as