Sub-wavelength nanostructured systems with tunable electromagnetic properties, such as hyperbolic metamaterials (HMMs), provide a useful platform to tailor spontaneous emission processes. Here, we investigate a system comprising Eu 3+ (NO3)3•6H2O nanocrystals on an HMM structure featuring a hexagonal array of Ag-nanowires in a porous Al2O3 matrix. The HMM-coupled Eu 3+ ions exhibit up to a 2.4-fold increase of their decay rate, accompanied by an enhancement of the emission rate of the 5 D0→ 7 F2 transition. Using finite-difference time-domain modeling, we corroborate these observations with the increase in the photonic density of states seen by the Eu 3+ ions in the proximity of the HMM. Our results indicate HMMs can serve as a valuable tool to control the emission from weak transitions, and hence hint at a route towards more practical applications of rare-earth ions in nanoscale optoelectronics and quantum devices.

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Light emitters in the vicinity of a hyperbolic metamaterial (HMM) show a range of quantum optical phenomena from spontaneous decay-rate enhancement to strong coupling. In this study, we integrate a monolayer molybdenum disulfide (MoS 2 ) emitter in the near-field region of the HMM. The MoS 2 monolayer has A and B excitons, which emit in the red region of the visible spectrum. We find that the B excitons couple to the HMM differently compared to A excitons. The fabricated HMM transforms to a hyperbolic dispersive medium at 2.14 eV, from an elliptical dispersive medium. The selective coupling of B excitons to the HMM modes is attributed to the inbuilt field gradient of the transition. The B exciton energy lies close to the transition point of the HMM, relative to the A exciton. So, the HMM modes couple more to the B excitons and the metamaterial functions as a selective coupler. The coupling strength calculations show that coupling is 2.5 times stronger for B excitons relative to A excitons. High near field of HMM, large magnitude, and the in-plane transition dipole moment of MoS 2 excitons, result in strong coupling of B excitons and formation of hybrid light-matter states. The measured differential reflection and photoluminescence spectra indicate the presence of hybrid light-matter states, i.e., exciton polaritons. Rabi splitting of 143.5 meV ± 14.4 meV at room temperature is observed. The low-temperature photoluminescence measurement shows mode anticrossing, which is a characteristic feature of hybrid states. Our results show that the HMM works as an energy-selective coupler for multiexcitonic systems as MoS 2 .