GaNP / GaP is promising for yellow-amber-red light emitting diodes ͑LEDs͒. In this study, pressure and temperature dependent electroluminescence and photocurrent measurements on bulk GaP / GaN 0.006 P 0.994 / GaP LED structures are presented. Below ϳ110 K, emission is observed from several localized nitrogen states. At room temperature, the band-edge energy increases weakly with pressure at a rate of +1.6 meV/ kbar, substantially lower than the ⌫ band gap of GaP ͑+9.5 meV/ kbar͒. Thus, despite the multiplicity of nitrogen levels, the band anticrossing model reasonably describes this system based on an average of the nitrogen states. Furthermore, carrier leakage into the X minima of GaP reduces the efficiency in GaNP-LEDs with increasing pressure. For a number of years, nitrogen has been added to the indirect semiconductor GaP to act as a radiative defect center to produce light emitting diodes ͑LEDs͒.1 Recently, there has been renewed interest in III-V-N semiconductors due to the large band-gap bowing that is observed in such materials when only a few percent of nitrogen is added. The interaction between the localized N states and the conduction band ͑CB͒ minimum has been effectively modeled with both the band anticrossing ͑BAC͒ model 2 and the empirical pseudopotential method.3 This has recently led to activity in dilute nitrides based on GaP where the fraction of nitrogen can be carefully controlled via molecular beam epitaxy ͑MBE͒ growth. Additionally, yellow-amber-red GaNP LEDs may offer better device characteristics than current AlInGaP devices due to a weaker dependence of the band gap 4 and lower thermal resistivity. 5 In this letter, we investigate the validity of a simple BAC model in GaNP-based materials and consider the factors limiting the electro-optic efficiency of LEDs based on GaNP.The devices studied here were grown by MBE and utilize simplified chip processing by one-step growth on transparent 350 m thick n-type GaP ͑100͒ substrates. The epitaxial layers consist of a 0.3 m thick n-GaP layer ͑Si doped͒, 0.15/ 0.1/ 0.15 m thick undoped GaP / GaN 0.006 P 0.994 / GaP active region, and 0.8 m thick p-GaP ͑Be doped͒ contact layer. LED chips were fabricated using Ge/ Au/ Ni/ Au and AuZn metallization for n-and p-type contacts, respectively.We employ temperature dependent measurements performed with a standard closed cycle cryostat setup over the temperature range of 70-300 K. This gives temperature and current dependencies of the electroluminescence ͑EL͒ spectra. The application of high hydrostatic pressure causes an increase in the direct band gap, and a reduction in the indirect X minima, thereby allowing investigations of the band structure and leakage effects into the indirect minima of GaP. Pressure dependent measurements were performed over the range of 0 -10 kbar using gaseous helium as the pressure medium. In the dilute nitrides, high pressure can also be used to tune the interaction between the nitrogen level͑s͒ and the conduction band of the host material, forming a useful means of investiga...