For this animation I have used an emission shader in a volumetric material for the first time. I added the shader on top of a volume scatter and a volume whatever shader and used a gradient curve to modify the density values for the emission shader a bit.
The input for the density function is a Point-Density Texture which is connected to a particle system.
The results aren' t quite as I expected them (which is kind of a recurring theme in my blender experiments :-) ) But I really like how it looks.
you can download the blend file here
volumetric density texture
point density smoke test
Dynamic Paint particle growth