Wurtzite
gallium phosphide (WZ GaP) has been predicted to exhibit a direct
bandgap in the green spectral range. Optical transitions, however,
are only weakly allowed by the symmetry of the bands. While efficient
luminescence has been experimentally shown, the nature of the transitions
is not yet clear. Here we apply tensile strain up to 6% and investigate
the evolution of the photoluminescence (PL) spectrum of WZ GaP nanowires
(NWs). The pressure and polarization dependence of the emission together
with a theoretical analysis of strain effects is employed to establish
the nature and symmetry of the transitions. We identify the emission
lines to be related to localized states with significant admixture
of Γ7c symmetry and not exclusively related to the
Γ8c conduction band minimum (CBM). The results emphasize
the importance of strongly bound state-related emission in the pseudodirect
semiconductor WZ GaP and contribute significantly to the understanding
of the optoelectronic properties of this novel material.