[kamiyu]

For fabrication of OLED and LEEC, what level of purity is needed. If I come up with a sample which is very emissive, is this OK already??

[Enthalpy]

From the time I tinkered with semiconductors, I remember that their process is so specific that answers exist only in semiconductor journals.

Yes, I would expect impurities to ruin the emissivity as the very first effect, but there can be other effects, including on the long term only - more so for surface devices like Mos.

If commercial versions of your device exist, you could compare the emissivities using a sensor, and maybe the effect of prolonged high-temperature operation.