We have used photoreflectance (PR) and photoluminescence (PL) measurements to characterize the optical properties of a series of strained InxGa1-xAs1-yNy thin films (x similar to 20%, y similar to 3%) grown by molecular beam epitaxy (MBE) on different GaAs substrates with the following surface orientations: (1 0 0), (5 1 I)A, (4 1 I)A, (3 1 I)A, and (I I I)A. The aim of our work is to investigate the effect of substrate orientation on the optical emission of (In, Ga)(As, N). Our results indicate that the growth direction affects the crystal quality, the N incorporation, and the optical properties of the films. (c) 2006 Elsevier B.V. All rights reserved.