  We study the internal dynamics of an elementary quantum system placed close
to a body held at a temperature different from that of the surrounding
radiation. We derive general expressions for lifetime and density matrix valid
for bodies of arbitrary geometry and dielectric permittivity. Out of
equilibrium, the thermalization process and steady states become both
qualitatively and quantitatively significantly different from the case of
radiation at thermal equilibrium. For the case of a three-level atom close to a
slab of finite thickness, we predict the occurrence of population inversion and
an efficient cooling mechanism for the quantum system, whose effective internal
temperature can be driven to values much lower than both involved temperatures.
Our results show that non-equilibrium configurations provide new promising ways
to control the state of an atomic system.
