What material is used to make luminescent placard on civil aircraft?
I don't know what exactly AD400 TV25/3881/83 is, but if you are talking about a sign like this:



It appears to be plastic and Larchfield sells them. This material AD400 TV25/3881/83 could very well be a type of plastic, but I don't know about it.

In my opinion, you can contact companies which make or sell them (Larchfield or this or this) to get more reliable information.