  Light-matter interaction dynamics is governed by the strength of local
coupling constants, tailored by surrounding electromagnetic structures.
Characteristic decay times in dipole-allowed fluorescent transitions are much
faster than mechanical conformational changes within an environment and, as the
result, the latter can be assumed static during the emission process. However,
slow-decaying compounds can break this commonly accepted approximation and
introduce new interaction regimes. Here, slow decaying phosphorescent compounds
are proposed to perform quantum sensing of nearby structure's motion via
observation of collective velocity-dependent lifetime distributions. In
particular, characteristic decay of an excited dye molecule, being comparable
with its passage time next to a resonant particle, is modified via
time-dependent Purcell enhancement, which leaves distinct signatures on
properties of emitted light. Velocity mapping of uniformly moving particles
within a fluid solution of phosphorescent dyes was demonstrated via analysis of
modified lifetime distributions. The proposed interaction regime enables
performing studies of a wide range of phenomena, where time-dependent
light-matter interaction constants can be utilized for extraction of additional
information about a process
