Many inorganic and organic persistent luminescence materials act as an optical energy storage medium to store the energy of incident photoexcitation into that of trapped electrons and holes until releasing it under external stimuli, such as focused ultrasound, near-infrared irradiation, and heat. We are developing an endogenous optical flow battery by delivering and circulating these trap-engineered phosphors in the bloodstream. Blood circulation is the body’s main mechanism to provide nourishment, such as oxygen, nutrients, and hormones, throughout the body. We argue that the same mechanism can be utilized to deliver photon energy via circulating trap-engineered phosphors, thus effectively turning the circulatory system into an in vivo optical flow battery. Specifically, circulating phosphors absorb and store light energy incident on the skin and release the energy as localized emission under spatiotemporally defined external stimuli, such as focused ultrasound, thus fulfilling the construction of a circulatory light source. Read our PNAS and Science papers to learn more.