Purple Light Captives?
As far as I can tell, there is no holding light unfortunately. There's a LOT of elements that are missing from MA, but think of this as v1 of MA (because it is). Hopefully they'll add things like that in the future...hopefully.
I think you mean the animation/emote Captured (Energy Field), That's teh closest I can think of from your description.
I hope the following is in MA somewhere, but I am not sure where. Remember the Lost being held in purple light in the red side mission arc to enter Cim? Is there a way to get stasis chambers to hold captives in the purple light until the chamber is destroyed, then the purple light quits, and the captives attack? If I can't get the purple light effect with the stasis chamber, under what options can I set up the rest of it? Thanks.