Kennard-Stepanov relation connecting absorption and emission spectra in   an atomic gas
  The Kennard-Stepanov relation describes a thermodynamic, Boltzmann-type scaling between the absorption and emission spectral profiles of an absorber, which applies in many liquid state dye solutions as well as in semiconductor systems. Here we examine absorption and emission spectra of rubidium atoms in dense argon buffer gas environment. We demonstrate that the Kennard-Stepanov relation between absorption and emission spectra is well fulfilled in the collisionally broadened atomic gas system. Our experimental findings are supported by a simple theoretical model. 
Peter Moroshkin, Lars Weller, Anne Sass, Jan Klaers, and Martin Weitz
physics.atom-ph