What is the action mechanism of plastic luminous agent?

The reason why plastic luminous agent can store light energy in plastic material after receiving sunlight or other illumination and can automatically emit light in the dark is related to its special structure and composition. Although there are many types of plastic luminous agents, their luminous process is basically the same, which consists of three steps: (1) the matrix lattice absorbs excitation energy; The matrix lattice transfers the absorbed excitation energy to the activated ions to excite them; The excited ions emit light and return to the ground state. The luminous process of the plastic luminous agent can be seen from the figure that the matrix, activator and sensitizer that make up the plastic luminous agent
Agents play different roles respectively, and jointly complete the functions of light absorption, light storage and light emission. The activator in the plastic luminous agent matrix forms an activation center, and the sensitizer forms a sensitization center. If the absorption of the matrix does not produce radiation, A absorbs excitation energy and produces radiation (including thermal diffusion) luminescence; S absorbs the excitation energy, transfers the energy to A, and is radiated by A, thus forming sensitized luminescence. Although the luminous process of different types of plastic luminous agents is roughly the same, it
The specific mechanism of luminescence may be different. The luminous mechanism of plastic luminous agent mainly includes energy transfer mechanism, electron transfer mechanism and hole transfer mechanism. Energy transfer is the process of energy transfer between defects and rare earth ions. For trivalent rare earths such as Ce3+, Pr3+ and Tb3+
Ions, which are easy to form tetravalent oxidation state, so the three elements can coexist in the matrix system in tetravalent oxidation state and +4 oxidation state respectively. In this way, RE4+ can be used as a hole trap center, and RE4 can be used as an electron trap center. These holes and electrons trapped by defect centers recombine under thermal disturbance, and the released energy is transferred to trivalent rare earth ionization.
Excites the ground state electrons to the excited state, and finally causes trivalent rare earth ions to automatically emit light in the dark. However, in the reducing atmosphere, the +4 oxidation state of these rare earth ions is not easy to form. At this time, the plastic luminous agent generates electrons and holes under the excitation of ultraviolet light or laser, and can be captured by different defects respectively. After the excitation stops, the energy generated by the recombination of electrons and holes in defects is transferred to rare earth ions. Because Ce3+, Pr3+ and Tb3+ have lower 5d-4f transition energies than other rare earth ions, the energy released by the recombination of electrons and holes matches the corresponding energy levels of Ce3+, Pr3+ and Tb3+ ions, and because the depth of electron and hole traps is appropriate, these ions can automatically emit light for a long time at room temperature. It should be pointed out that in the matrix system with alkaline earth ions as the component, oxygen ion vacancies play a vital role, because oxygen ion vacancies can trap electrons and become electron traps. As for the hole traps, they can be A13+ ion vacancies or other defects in the system, even rare earth ions such as Ce3+. The existence of oxygen ion vacancies in these systems has been confirmed by electron paramagnetic resonance spectroscopy (EPR).