The photoluminescence properties of metal-organic chemical vapor deposition GaAs:Er were investigated as a function of temperature and applied hydrostatic pressure. The4I13/2→4I15/2Er3+emission energy was largely independent of pressures up to 56 kbar and temperatures between 12 and 300 K. Furthermore, no significant change in the low temperature emission intensity was observed at pressures up to and beyond the&Ggr;-Xcrossover at ∼41 kbar. In contrast,AlxGa1−xAs:Eralloying studies have shown a strong increase in intensity near the &Ggr;-Xcrossover atx∼0.4.These results suggest that the enhancement is most likely due to a chemical effect related to the presence of Al, such as residual oxygen incorporation, rather than a band structure effect related to the indirect band gap or larger band gap energy. Modeling the temperature dependence of the 1.54 &mgr;mEr3+emission intensity and lifetime at ambient pressure suggested two dominant quenching mechanisms. At temperatures below approximately 150 K, thermal quenching is dominated by a ∼13 meV activation energy process which preventsEr3+excitation, reducing the intensity, but does not affect theEr3+ion once it is excited, leaving the lifetime unchanged. At higher temperatures, thermal quenching is governed by a ∼115 meV activation energy process which deactivates the excitedEr3+ion, quenching both the intensity and lifetime. At 42 kbar, the low activation energy process was largely unaffected, whereas the higher activation energy process was significantly reduced. These processes are proposed to be thermal dissociation of the Er-bound exciton, and energy back transfer, respectively. A model is presented in which the Er-related electron trap shifts up in energy at higher pressure, increasing the activation energy to back transfer, but not affecting thermal dissociation of the bound exciton through hole emission. ©1997 American Institute of Physics.