After receive some other questions about emissive maps in blender, I did this small videoutorial demonstrating the way I use to do it, hope it helps to anyone interested.
In case you don’t know what is an emissive map, read this:
An emissive map uses colours to simulate a glowing effect within the texture. The effect of an emissive map does not go beyond the limits of an object, and therefore cannot be used to generate glows around the rest of the scene or the surrounding objects. (Autodesk Wikihelp)