The long-range, short-range model of the nitrogen isoelectronic impurity in Ga(As,P) is discussed in terms of the results of recent photoluminescence and lifetime measurements. The predictions of the theory are shown to depend sensitively upon the strength of the coupling among the states produced separately by the long- and short-range parts of the potential: The strength of the coupling reflects the specific model of potential used in all cases treated. Strong coupling yields theoretical energies whose general composition dependence mirrors the features of the data. The effect of consideration of the L-conduction-band minima is smaller. Determination of potential parameters from experimental energies indicates a range 20-25. Luminescence calculations require an accurate treatment of the continuum contribution. Predictions of the theory are in good agreement with available data. Inclusion of L indicates the existence of an excited nitrogen state in GaP. No internal inconsistencies in the theory are found. © 1980 The American Physical Society.21834783490