  We develop a rigorous, field-theoretical approach to the study of spontaneous
emission in inertial and dissipative nematic liquid crystals, disclosing an
alternative application of the massive Stueckelberg gauge theory to describe
critical phenomena in these systems. This approach allows one not only to
unveil the role of phase transitions in the spontaneous emission in liquid
crystals but also to make quantitative predictions for quantum emission in
realistic nematics of current scientific and technological interest in the
field of metamaterials. Specifically, we predict that one can switch on and off
quantum emission in liquid crystals by varying the temperature in the
vicinities of the crystalline-to-nematic phase transition, for both the
inertial and dissipative cases. We also predict from first principles the value
of the critical exponent that characterizes such a transition, which we show
not only to be independent of the inertial or dissipative dynamics, but also to
be in good agreement with experiments. We determine the orientation of the
dipole moment of the emitter relative to the nematic director that inhibits
spontaneous emission, paving the way to achieve directionality of the emitted
radiation, a result that could be applied in tuneable photonic devices such as
metasurfaces and tuneable light sources.
