  The optical response of phosphorene can be gradually changed by application
of moderate uniaxial compression, as the material undergoes the transition into
an indirect gap semiconductor and eventually into a semimetal. Strain tunes not
only the gap between the valence band and conduction band local extrema, but
also the effective masses, and in consequence, the exciton anisotropy and
binding strength. In this article, we consider from a theoretical point of view
how the exciton stability and the resulting luminescence energy evolves under
uniaxial strain. We find that the exciton binding energy can be as large as
0.87 eV in vacuum for 5% transverse strain, placing it amongst the highest for
2D materials. Further, the large shift of the luminescence peak and its linear
dependence on strain suggest that it can be used to probe directly the strain
state of single-layers.
