In the past, the radioactive element was radium, which has a half-life of 1600 years. In these products, the phosphor is mixed with a radioactive element, and the radioactive emissions (see How Nuclear Radiation Works) energize the phosphor continuously. The most common place is on the hands of expensive watches. Occasionally you will see something glowing but it does not need charging. The phosphor is mixed into a plastic and molded to make most glow-in-the-dark stuff. It has a much longer persistence than Zinc Sulfide does. Strontium Aluminate is newer - it's what you see in the "super" glow-in-the-dark toys. Two phosphors that have these properties are Zinc Sulfide and Strontium Aluminate. To make a glow-in-the-dark toy, what you want is a phosphor that is energized by normal light and that has a very long persistence. The length of time that they glow after being energized (known as the persistence of the phosphor).The color of the visible light that they produce.The type of energy they require to be energized.
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