Spontaneous emission dynamics of Eu3+ ions coupled to hyperbolic metamaterials

Abstract

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 Eu3+(NO3)3·6H2O nanocrystals on an HMM structure featuring a hexagonal array of Ag nanowires in a porous Al2O3 matrix. The HMM-coupled Eu3+ ions exhibit up to a 2.4 fold increase in their decay rate, accompanied by an enhancement of the emission rate of the 5D0 → 7F2 transition. Using finite-difference time-domain modeling, we corroborate these observations with the increase in the photonic density of states seen by the Eu3+ ions in the proximity of the HMM. Our results indicate that HMMs can serve as a valuable tool to control the emission from weak transitions and, hence, hint at a route toward more practical applications of rare-earth ions in nanoscale optoelectronics and quantum devices. M.L. and V.M.M. acknowledge support from the National Science Foundation through Grant No. NSF-1906096; C.A.M. acknowledges support from the Department of Energy through Grant No. BES-DE-SC0020638. All the authors acknowledge access to the facilities of the NSF CREST IDEALS, Grant No. NSF-HRD-1547830. V.M.M. and J.K.B. also acknowledge the program Scheme for the Promotion of Academic and Research Collaboration (SPARC), Ministry of Human Resources Development (MHRD), India, for supporting travel between India and the U.S. to foster international collaboration. We thank Daniela Pagliero and Artur Lozovoi for assistance with the experimental setup. We are also indebted to Fernando Meneses for useful discussions on the HMM structure.