Fluorescent dye can be a great addition for decorating around the house for Halloween, especially for a haunted one. Creating your own fluorescent dye is a simple experiment, as long as you've got the proper chemicals and safety gear. Nurd Rage details the chemical process of creating your own fluorescein below.
The process, per Nurd Rage's directions:
Combine 166 mg of phthalic anhydride, 220mg of resorcinol and 3 drops of concentrated sulfuric acid. Heat to 200 degrees celsius for 5 minutes. The crude fluorescein produced is dissolved in dilute sodium hydroxide solution (300mg in 10mL of water). To demonstrate fluorescence, a few drops of the solution are dropped into water under ultraviolet light.
You can use the dye to fill up jars and containers, and it works well with potion/witch jars to give it that added spooky glow effect. You can even get more creative and throw in other props into the jar like eyeballs...or even a severed hand.
If you don't have the proper chemicals to make your own fluorescent dye, you can always purchase some from your local craft shop.