PPV was used as the emissive layer in the first polymer light-emitting diodes. OLEDs consist of an emissive and conductive layer. Electrical impulses travel through the conductive layer and produce light at the emissive layer. Below the electron emission saturation limit the contactor acts as a bipolar emissive probe. Heating the filament in a hydrocarbon atmosphere carburizes the surface and stabilizes the emissive layer. Window glass is by nature highly thermally emissive, as indicated in the table above. This also will make these materials non emissive into the environment. Emissive probes use an electrode heated either electrically or by the exposure to the plasma.