Field emission displays can be seriously limited by current degradation of Mo field emitter arrays, primarily due to inadequate vacuum conditions inside their thin vacuum packages. Most lifetime studies describe the deleterious effects of short exposures to oxygenic gases on device performance. Here, we review experimental results on the emission characteristics of molybdenum field emitter arrays in a variety of gas ambients for extended periods. We find that even in inert gas, the emission current degrades rapidly, comparable to that observed in oxygenic gas ambients. Surprisingly, after exposure when the device is again operated under high vacuum conditions, various levels of current recovery can be observed. No evidence for ion sputter damage is observed. Existing degradation models do not provide an adequate explanation for this behavior. Rather, we suggest that these results point toward a model common for all gaseous ambients based on shallow implantation of ions into the field emitter tips. This creates a near surface layer that modifies the tunneling barrier, and thus subsequently the emission current. Support for this mechanism comes from several experimental observations. The implant degradation model is also consistent with devices that incorporate a field emitter ion pump process as a means to reduce pressure in the sealed vacuum package. (C) 2003 American Vacuum Society.