  The strong coupling between spin, lattice and electronic degrees of freedom
in magnetic materials can produce interesting phenomena, including multiferroic
and magnetodielectric (MD) behavior, and exotic coupled excitations, such as
electromagnons. We present a temperature- and magnetic-field-dependent
inelastic light (Raman) scattering study that reveals the emergence of vibronic
modes, i.e., coupled vibrational and crystal-electric-field (CEF) electronic
excitations, in the unconventional rare-earth MD material,
$\text{Ce}_2\text{O}_3$. The energies and intensities of these emergent
vibronic modes are indicative of enhanced vibronic coupling and increased
modulation of the dielectric susceptibility in the N\'eel state ($T_\text{N}
\approx 6.2\,\text{K}$). The field-dependences of the energies and intensities
of these vibronic modes are consistent with a decrease of both the vibronic
coupling and the dielectric fluctuations associated with these modes below
$T_\text{N}$. These results suggest a distinctive mechanism for MD behavior in
$\text{Ce}_2\text{O}_3$ that is associated with a field-tunable coupling
between CEF and phonon states.
