1, energy level structure: In the electronic energy level structure of molecules or atoms, S 1 and T 1 are the lowest excited states, and the energy level difference between them is very small, so that electrons will emit a specific wavelength in the visible spectrum when they return to the ground state from these two energy levels.

2. Excitation mode: The excitation mode of fluorescence and phosphorescence is to make electrons jump from the ground state to the excited state of S 1 or T 1 by absorbing photon energy of a certain wavelength, at which time the electrons will be at the lowest vibration level. When electrons return to the ground state from S 1 or T 1, the emitted spectrum will also be at the corresponding energy level, which is the wavelength of the visible region.