Electric field induced narrowing of exciton line width
  Considering effects of electric field on the low temperature absorption line of quantum well excitons, we show that, for moderate strength of the electric field, the main contribution to the field dependence of the line-width results from field induced modifications of inhomogeneous broadening of excitons. We find that the strength of the random potential acting on quantum well excitons due to alloy disorder and interface roughness can either decrease or increase with field depending upon the thickness of the well. This means that under certain conditions one can observe counterintuitive narrowing of exciton spectral lines in electric field. 
I. V. Ponomarev, L. I. Deych, and A. A. Lisyansky