Electrical control of optical emitter relaxation pathways enabled by graphene

Abstract

Controlling the energy flow processes and the associated energy relaxation rates of a light emitter is of high fundamental interest, and has many applications in the fields of quantum optics, photovoltaics, photodetection, biosensing and light emission. While advanced dielectric and metallic systems have been developed to tailor the interaction between an emitter and its environment, active control of the energy flow has remained challenging. Here, we demonstrate in-situ electrical control of the relaxation pathways of excited erbium ions, which emit light at the technologically relevant telecommunication wavelength of 1.5 µm. By placing the erbium at a few nanometres distance from graphene, we modify the relaxation rate by more than a factor of three, and control whether the emitter decays into either electron-hole pairs, emitted photons or graphene near-infrared plasmons, confined to <15 nm to the sheet. These capabilities to dictate optical energy transfer processes through electrical control of the local density of optical states constitute a new paradigm for active (quantum) photonics.Spontaneous emission constitutes a canonical example of energy flow from an excited light emitter into its environment, where energy relaxation takes place via photon emission. Alternatively, for an emitter in the vicinity of a solid, energy relaxation can occur through channels involving electronic excitations, such as electron-hole pairs and collective charge oscillations (plasmons). Tailoring spontaneous emission by modifying the local density of optical states (LDOS), which governs the emitter-environment interactions [1,2], has been achieved using, amongst others, optical cavities [3][4][5][6], photonic crystals [7,8], and metallic nanostructures [9]. In these systems the LDOS available for the light emitters is typically a fixed property that depends only on the type and geometry of the material system. Here, we control electrically and in-situ the local density of optical states and therefore the energy relaxation rate of a nearby emitter, by employing graphene. Specifically, we demonstrate in-situ tuning of the magnitude and character of the energy transfer pathways from optically excited erbium ions -emitters for near-infrared light that are used as a gain medium in telecommunication applications [10,13]. This control enables new avenues in a range of fields, covering photovoltaics [11,12] The ability to control in-situ the LDOS requires a material for which the optical excitations that occur for a specific emission energy can be modified. Because graphene is gapless and it has a Fermi energy that is electrostatically tunable up to optical energies of ∼1 eV, it can effectively behave as a semiconductor, a dielectric, or a metal. Here, we propose to use these material characteristics to electrically control the relaxation rate and energy transfer processes of a dipolar emitter at subwavelength distance from the graphene. The concept of our experiment is shown in Fig. 1a, schematically representing the gate-tunable ener...

Raman spectroscopy of electrochemically gated graphene transistors: Geometrical capacitance, electron-phonon, electron-electron, and electron-defect scattering

“…42 Recently, electrochemically-gated graphene FETs have been successfully employed to investigate electron-phonon coupling, 41,[43][44][45][46][47] but also bandgap formation in bilayer graphene, 48,49 electron transport at high carrier density, 42,50,51 many-body phenomena, 6 as well as to electrically control the interaction between nano-emitters and graphene. 52,53 In such studies, an accurate determination of E F (hence of the gate capacitance) as a function of the gate voltage is a critical requirement. However, as opposed to solid state FETs, in which the oxide dielectric constant and thickness can be known with accuracy, the thickness of the electrical double layer may be highly arXiv:1502.06849v2 [cond-mat.mes-hall] 16 Apr 2015 sensitive to the device geometry, fluctuate spatially and vary over time.…”

Towards graphene plasmon-based free-electron infrared to X-ray sources

“…Importantly, the observed plasmon lifetimes are gradually improving due to higher quality samples and fabrications of Van der Waals heterostructures [3], and are expected to increase further with advances in fabrication techniques (e.g., [30]). Similar progress is also seen for GPs of shorter free space wavelengths [31], with reports of compelling evidence [32] and recent clear signatures [33] in the near-infrared. Observations are also anticipated in the visible regime [4].…”

Purcell effect at the percolation transition

“…In addition, photonic crystals [12], optical cavities [13], metallic nanostructures [14,15], plasmonic cloaks [16,17], hyperbolic metamaterials [18] and negative index materials [19] are some examples of systems in which the LDOS and SE rate are dramatically affected by unusual photonic properties of the environment. Besides, gated and magnetic field biased graphene correspond to systems where active control of the Purcell effect can be implemented [20,21]. However, in most of previous examples the modification of the LDOS involves sophisticated nano-fabrication techniques and/or complex nanostructures.…”