I agree with your choice of "phosphorescence"; it seems to fit the term you need here as it describes the effect of storing light and then radiating it outwards. Luminousity is slightly off as it describes the effect of something producing light its self. As the Japanese sentence you included speaks of light glowing in the dark, the term "light storage" or "light absorption" would seem slightly inadiquate as they don't speak of radiating the light later (even if it is implied).
蓄光 is also called 燐光(りんこう).