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Photoluminescence (PL), X-ray diffraction (XRD) and Raman spectra have been measured to characterize the effects of phosphorus on the optical and structural properties of GaN1−xPx alloys with x&les;15%, grown by means of light-radiation heating, low-pressure metal-organic chemical vapor deposition. The PL spectra of GaN1−xPx show the largest red shift of 100 meV from the band-edge emission of GaN. XRD rocking curves show that the (0 0 0 2) peak of GaN1−xPx shifts to smaller angles with increasing P content. The Raman spectra of GaN1−xPx, recorded in backscattering geometry, exhibit four new vibrational modes at 256, 314, 377 and 428 cm−1 compared with an undoped GaN sample. The modes at 377 and 428 cm−1 are attributed to gap modes related to the Ga–P bond vibrations, whereas the other two modes at 256 and 314 cm−1 are assigned to phosphorus clusters and disorder-activated scattering, respectively. The frequency of the A1 (LO) mode is found to decrease with increasing x at a much high rate of approximately 268 cm−1/x for x<0.03. This red shift is attributed to the effects of alloying and strain. Furthermore, we have not observed characterizations related to GaP resulted from the phase separation from PL, XRD and Raman spectra of all investigated GaN1−xPx samples. [Copyright &y& Elsevier]