Phosphorus

The first form or sighting of Phosphorus was in 1669. Phosphorus emits a faint glow upon exposure to oxygen.

How To Get
You can get Phosphorus by decomposing Glowstone (block or dust, doesn't matter) and bones as well as brown mushrooms.

You can also get Phosphorus by fusing two elements whose atomic number equals 15 such as Oxygen (Atomic Number: 8) and Nitrogen (Atomic Number: 7).

Other Information
Atomic Number: 15

Element Symbol: P