Is the pointer of the watch coated with phosphor? Why does it glow at night? What is the principle?

The hands of fluorescent watches are coated with fluorescent powder, which absorbs energy during the day and slowly releases it in the form of light, so there is a so-called "night light".

The luminous time of a luminous watch is limited by the time and intensity of absorbing light, which generally won't last long, and it will go out by itself after a long time in the dark. Later, scientists coated the phosphor with a layer of artificial radioactive substance, so that the phosphor was always irradiated by rays, so that the fluorometer could always emit light, and there was no longer the problem of impermanence.

Extended data

Luminous coating (luminescent material): a new generation of luminescent material, applied to hands and dials, which is irradiated by sunlight during the day and electrons jump to high energy level to absorb energy; At night, electrons jump from high energy level to low energy level, giving off light without radiation. In this way, you can read the time by distinguishing the hands where there is no light.

Radioactive noctilucent powder is a kind of luminescent powder, which is doped with radioactive substances, and excites the phosphor to emit light through the continuous radiation of radioactive substances. This luminous powder has a long luminous time, but its application range is small because of its toxicity and environmental pollution.

The main luminescent materials at home and abroad are ZnS (zinc sulfide), SrS (strontium sulfide) and CaS (calcium sulfide), which emit green light and yellow light. However, SrS and CaS materials are easy to deliquesce, which brings difficulties to their wide application. Therefore, the market is dominated by ZnS luminescent materials. However, the rest glow time is only 1 ~ 3 hours, which is easy to deteriorate and turn black in strong light (such as sunlight), ultraviolet light and humid air, and its application in many fields is limited.

Baidu encyclopedia-fluorescent watch