Multifold Enhancement of Quantum Dot Luminescence in Plasmonic Metamaterials

We report that hybridizing semiconductor quantum dots with plasmonic metamaterial leads to a multifold intensity increase and narrowing of their photoluminescence spectrum. The luminescence enhancement is a clear manifestation of the cavity quantum electrodynamics Purcell effect and can be controlled by the metamaterial’s design. This observation is an essential step towards understanding loss compensation in plasmonic metamaterials with gain media and for developing metamaterial-enhanced gain media.

Figure 1

(a) Schematic of a plasmonic metamaterial functionalized with QDs. (b) Measured spectra of transmission $T$, reflection $R$, and absorption $A$ for a QD-coated metamaterial with a unit cell size of $D=545\mathrm{nm}$. The insets show a sketch of QDs in the resonant mode volume, as seen from the substrate side, and a scanning electron micrograph of the unit cell (without QDs). Feature sizes: unit cell $D=545\mathrm{nm}$, horizontal slit $a=470\mathrm{nm}$, top vertical slit and gap $t=g=170\mathrm{nm}$, and slit width $w=65\mathrm{nm}$.

Figure 2

Photoluminescence controlled by plasmonic metamaterials. (a) Photoluminescence spectra of the QDs without (top) and with a metamaterial layer accompanied by Gaussian fits (solid lines). Dotted lines indicate metamaterial absorption spectra. (b) Intensity enhancement and FWHM of the QD-metamaterial photoluminescence spectra. Enhancement is normalized to the photoluminescence peak intensity measured without a metamaterial layer. Reference values measured without a metamaterial layer are indicated by arrows.

Figure 3

Polarization dependence of (a) photoluminescence and (b) absorption, measured for the metamaterial with $D=545\mathrm{nm}$. Linear polarizations $x$ and $y$ are introduced in Fig. 1b, while $xy$ is the intermediate polarization at 45° to $x$.

Figure 4

Nature of the photoluminescence change in the plasmonic metamaterial. (a) Energy diagram of the QD-metamaterial coupled system. (b–f) Comparison of the measured photoluminescence (data points) with ${\chi }_A(\lambda )=P{L}_0(\lambda )\times A(\lambda )$ (lines) for metamaterials with different unit cell sizes ranging from $D=545\mathrm{nm}$ to 645 nm. Here, $P{L}_0(\lambda )$ is normal QD photoluminescence without a metamaterial structure, and $A(\lambda )$ is the metamaterial’s absorption spectrum.