The micro mechanism of anti-Stokes fluorescent cooling was investigated on
molecular or ionic scale. A new conception of single molecule-photon cryoco
oler (SMPC) was given, and the smallest cryocooler in the world was predict
ed. We described SMPC and its running principle in detail. The quantum tran
sition processes of SMPC and the largest cooling coefficient that SMPC can
get in an optical transition were given. Also we studied the random propert
y of SMPC in cooling processes. The thermodynamic behavior of single Yb3+ i
on as a photon cryocooler was imitated.