 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 7c symmetry and not exclusively related to the 
 8c 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 . 
Supplementary Material