The spectra of high surface area amorphous oxide AlPO, AlGaPO, and GaPO were compared with those of high surface amorphous oxynitrides AlPON and AlGaPON with similar O/N ratio and with that of the nitride GaN. This allowed us to make a correct assignation of the bands in their IR vibrational spectra, especially those in the new family of solids named galloaluminophosphate oxynitride, AlGaPON. The substitution of aluminum atoms by gallium induces a shift of the framework band vibrations due to a second-neighbor effect. The introduction of nitrogen in the network of the oxide phosphate produces a broadening and poor definition of the structural bands due to a collapse of the structure. NH4+, coordinated NH3, -NH2, and -NH- species are identified on the surface of the AlGaPON solid. A thermal treatment under NH3 allows us to propose the following nitridation sequence: M-O-NH4+ and/or M-NH3 --> M-NH2 --> M-NH-M --> N3-.