  Epsilon-near-zero (ENZ) materials have been demonstrated to exhibit unique
electromagnetic properties. Here we propose the concept of radiative energy
bandgap for an ENZ nanoparticle coupled with a quantum emitter (QE). The
radiative emission of the coupled QE-nanoparticle can be significantly
suppressed around the ENZ frequency and substantially enhanced otherwise,
yielding an effective energy bandgap for radiation. This suppression is
effectively invariant with respect to the particle size and is therefore an
intrinsic property of the ENZ material. Our concept also heralds an alternative
pathway to quench the emission from a QE, which may find potential application
in quantum information storage.
