Multifold Enhancement of Quantum Dot Luminescence in Plasmonic Metamaterials

Abstract

We report that hybridizing semiconductor quantum dots with plasmonic metamaterial leads to a multi-fold intensity increase and narrowing of their photoluminescence spectrum. The luminescence enhancement is a clear manifestation of the cavity quantum electrodynamics Purcell effect that can be controlled by the metamaterial's design. This observation is an essential step towards understanding loss compensation in metamaterials with gain media and for developing metamaterial-enhanced gain media.Control of Joule losses is a key challenge for plasmonic and metamaterial technologies. Losses hamper the development of negative index media for super-resolution and optical cloaking devices, and plasmonic data processing circuits. Lowering losses is also crucially important for the performance of spectral filters, delay lines and, in fact, practically any other metamaterial and plasmonic applications [1]. Although using superconducting metamaterials can largely eliminate losses in THz and microwave metamaterials [2], Joule losses at optical frequencies are unavoidable. Recent works report compensation of losses with gain in metamaterials aggregated with semiconductor quantum dots (QDs) [3] and organic dyes [4] embedded into the metal nanostructures. Parametric metamaterials gain systems are also under investigation in theory [5][6][7]. Another grand goal of active metamaterials research is to improve laser gain media and to develop a 'lasing spaser' device: a 'flat' laser with emission fueled by plasmonic excitations in an array of coherently emitting meta-molecules [8]. An essential part of this development shall be the study of luminescence of active material hybridized with plasmonic nanostructures that could support collective, coherent plasmonic excitations in the lasing spaser. Here we report the first study of photoluminescence of semiconductor QDs hybridized with asymmetric split-ring plasmonic metamaterial. This type of metamaterial supports a closed-mode Fano-type excitation which has the key characteristics required for the lasing spaser application: the mode is formed by collective interactions between individual meta-molecules that shall ensure coherent laser action [9]. In this letter, we experimentally demonstrate that the photoluminescence properties of QDs can be greatly enhanced by the plasmonic metamaterial. Figure 1(a) schematically illustrates a plasmonic metamaterial combined with QDs. The metamaterials studied here consist of periodic arrays of asymmetrically split ring slits (negative structure), which have been successfully applied to switching, nonlinear and sensor applications [10]. The metamaterial arrays with a total size of 40 × 40 µm each were fabricated by focused ion beam milling in a 50nm-thick gold film on a glass substrate [see inset of Fig. 1(b)]. In order to systematically investigate the correlation between QD photoluminescence spectrum and the spectral position of the Fano plasmonic metamaterial resonance, we manufactured five metamaterial arrays with different unit cell sizes rangin...

Dual-channel spontaneous emission of quantum dots in magnetic metamaterials

“…In contrast to previous work investigating PL enhancement in single nanoparticles and nanoantennas 3,40,41 or in Fano-type 30,42,43 and hyperbolic metamaterials 31,32 , our SRR metamaterial supports both electric and magnetic modes that are spectrally matched to the emission of semiconductor QDs at around l QD ¼ 800 nm wavelength. Since both modes in our metamaterial can be engineered independently from each other, our QD metamaterial offers new opportunities to tailor the spontaneous emission of quantum emitters into two independent radiative decay channels.…”

“…Moreover, shape variations can clearly be identified among the three different samples, particularly for the electric mode, where the spectral mode position for sample A to sample C gradually shifts out of resonance with the QD PL. In order to compare these experimental findings with predictions from our simple model, we calculate the PL line shape w calc ðlÞ along the lines of Tanaka et al 30 Generally, the PL line shape consists of an enhanced and spectrally modified contribution from the coupled QDs, and an undisturbed contribution from the uncoupled QDs, yielding…”

“…In our simple toy model we treat each mode of the SRR metamaterial equivalent to a microcavity with resonance frequency o cav , linewidth Do cav ¼ 2pDf cav and an ultrasmall (open) mode volume V m 30,61,62 . The maximum Purcell factor for optimal spatial and polarization overlap is then given by 61,62 …”

“…An important step in controlling the process of loss compensation is the study of coupling of quantum emitters such as quantum dots (QDs) with metamaterials. In such structures, the hybridization of QDs with electric resonances of a metamaterial can lead to photoluminescence (PL) enhancement and modification of the PL properties that can be controlled by the metamaterial design 30,31 . Topological transitions in hyperbolic metamaterials 32 have also shown an important avenue to alter the photonic density of states by changing the isofrequency surfaces via plasmonic resonances.…”

Nanoantenna enhanced emission of light-harvesting complex 2: the role of resonance, polarization, and radiative and non-radiative rates

“…Another effect is the modification of the emission spectrum, as the antenna most strongly enhances transitions resonant with the antenna. [19][20][21][22][23] Most importantly, nanoantennae are able to increase the fluorescence signal; the total enhancement is given by the product of excitation-enhancement and QY-enhancement. The intrinsic QY of a fluorophore (QY 0 ) is given by: QY 0 = k r0 /(k r0 + k nr0 ), with k r0 and k nr0 being the intrinsic radiative and non-radiative decay rates.…”