Luminescent materials store sunlight and light from lighting and can emit light for several hours, so they are used as light sources that do not require electric power, such as clock faces and emergency exit lights.However, inorganic materials containing rare metals such as europium are used, and high temperature treatment of 1000 ° C or higher and many complicated processes are required for synthesis.Due to such resource and economic constraints, the use of phosphorescent materials is still limited.

　In this study, it was found that phosphorescent emission can be achieved simply by mixing two organic molecules with a simple structure.When this mixture of organic molecules absorbs light, charges are transferred from the electron donor material to the electron acceptor material, and a charge separation state is formed.This time, we succeeded in stabilizing this charge separation state, which is generally regarded as unstable.

　This stabilized charge separation state returns to a state in which light can be emitted again by transferring charges in the opposite direction to the initial state with a certain probability, and it becomes possible to extract the energy as light.

　The two organic molecules used can be easily synthesized and simply mixed, eliminating the need for complicated processes.In addition, by designing the optimum molecule based on the phosphorescent mechanism elucidated this time, it is possible to easily improve the emission duration and emission efficiency and control the emission color.Furthermore, since it is possible to impart functions that are difficult to realize with existing inorganic phosphorescent materials such as solubility in solvents, transparency, and flexibility, it is expected to open up new applications for phosphorescent materials.

Paper information:[Nature] Organic long persistent luminescence