  Semiconductors in all dimensionalities ranging from 0D quantum dots and
molecules to 3D bulk crystals support bound electron-hole pair quasiparticles
termed as excitons. Over the past two decades, the emergence of a variety of
low-dimensional semiconductors that support excitons combined with advances in
nano-optics and photonics has burgeoned a new area of research that focuses on
engineering, imaging, and modulating coupling between excitons and photons,
resulting in the formation of hybrid-quasiparticles termed exciton-polaritons.
This new area has the potential to bring about a paradigm shift in quantum
optics, as well as classical optoelectronic devices. Here, we present a review
on the coupling of light in excitonic semiconductors and investigation of the
unique properties of these hybrid quasiparticles via both far-field and
near-field imaging and spectroscopy techniques. Special emphasis is laid on
recent advances with critical evaluation of the bottlenecks that plague various
materials towards practical device implementations including quantum light
sources. Our review highlights a growing need for excitonic materials
development together with optical engineering and imaging techniques to harness
the utility of excitons and their host materials for a variety of applications.
