White Phosphorus glows in the dark due to:

White phosphorus (P4) is a highly reactive non-metal allotrope that is stored in water because it spontaneously catches fire when exposed to atmospheric air [1]. The characteristic glow it exhibits in the dark is known as chemiluminescence [2]. This phenomenon occurs due to the slow oxidation of phosphorus when it comes into contact with oxygen in the air [2]. During this process, the energy released from the chemical reaction is emitted as light rather than heat, creating a faint green glow [2]. While the term "phosphorescence" was historically used to describe this effect, it is scientifically classified as chemiluminescence because the light is a product of a chemical reaction [2]. Phosphorus is a poor conductor of electricity, and its glow is unrelated to its amorphous character or ignition temperature [2].

Sources

1. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 4: The World of Metals and Non-metals > Activity 4.8: Let us explore > p. 53
2. [2] https://www.sciencedirect.com/science/article/abs/pii/B9780128001370000017