Excitons bound to nitrogen impurity in GaP-rich A(3)B(5) alloys are investigated. It is shown that crystal lattice deformation, induced by the isoelectronic trap, cause additional shift of the spectral lines. Substitutional atoms give rise to an electric field due to the intrinsic piezoelectric effect and cause dispersion of interatomic distances. This effects determine the shape of spectral components. (C) 2002 Elsevier Science Ltd. All rights reserved.