Cubic phase CsPbI3 quantum dots (α-CsPbI3 QD), as a new kind of semiconductor quantum dots, bring great hope for basic research and application of optoelectronic devices. However, so far, due to its highly unstable ionic structure and low phase stability, a stable sub-5nm α-CsPbI3 has rarely been found so far. Yao et al. reported a new strontium doping and iodide passivation strategy to stabilize α-CsPbI3, and realized the simple synthesis of α-CsPbI3 QD, which has a series of controllable sizes, down to sub-5 nm. Studies have shown that the doped strontium ions can significantly increase the formation energy of α-CsPbI3 quantum dots, thereby reducing structural deformation, thereby stabilizing the cubic phase of a few nanometers in size. The size of the prepared stable α-CsPbI3 QD ranges from 15 nm to 5 nm. The red LED made based on α-CsPbI3 quantum dots exhibits high brightness (1250 cd m-2 at 9.2 V) and good operational stability.