Pro, it is the function of phosphor. Phosphor itself has no radiation, but its luminescence depends on the excitation of other radiation sources. Therefore, phosphors are often mixed with trace radioactive substances, while those without radioactive substances can only maintain fluorescence for a short time after strong light irradiation. When you see the light from the fluorescent toy, it means that you are exposed to radiation. The greater the fluorescence intensity, the greater the radiation. Of course, its radiation dose is large and small, and shoddy toys may be very unsafe. It's ok to play occasionally, and don't put it near.