Luminescence principles and material classifications in watches

Matter luminescence phenomena are generally divided into two categories: one is when a substance is heated, producing thermal radiation and emitting light, and the other is when a substance is excited to absorb energy, transitioning to an excited state (an unstable state) and then returning to the ground state while releasing energy in the form of light. The luminous coating used on watches utilises this second category of principles, which is that fluorescent materials emit light after being excited.

Types of luminous materials

Traditional luminous coating materials can be divided into self-luminous and storage-luminous types. Self-luminous phosphors mostly rely on trace radioactive substances they carry to emit rays that excite the phosphor to glow. Storage-luminous phosphors, on the other hand, contain virtually no radioactive substances, but they need to absorb and store a sufficient intensity of external light beforehand, transitioning their own electrons from a low energy level to a high energy level to store them. When the surrounding environment becomes dark, they slowly release the absorbed energy step by step; at this point, electrons transition from high to low energy levels, and the phosphor begins to glow. Since the storage-luminous type does not carry ray-exciting materials itself, its afterglow persistence is temporarily inferior to that of the self-luminous type.