How to make phosphorescent material I was wondering if it's possible to make a phosphorescent material that stores the light-energy. I don't mean like fluorescent just by putting a emmision shader. 

I mean if light shines on it and then you mute the light, the material stores the light for a period of time until it fades out into darkness. You get this material sometimes on the pointer of analog wristwatches or like on fluorescent jackets. 

Hope my explanation is clear
I provided a video for better clarification, also used Eevee because the render is fast, but you can use cycles too.

What you want is to simply animate a emission property and a light brightness, in the case of cycles, you could use only the emission shader.

You will also need another shader when the light fades off, so you mix the emission with the other shader, for a nice effect, I applied the same texture to the emitter. To the sphere to not cast shadow, I simply set the shadows to none in the materials tab.