A method for making a tris-(8-hydroxyquinoline) aluminum (Alq3) nano-crystals includes the steps of: (a) dissolving Alq3 powders into a solvent to form a solution A; (b) dissolving a surfactant in water to achieve a solution B; (c) uniformly mixing the solution A and the solution B to form a latex C; and (d) removing the solvent from the latex C, and subsequently, subjecting the remaining solute to centrifugal separation to form Alq3 nano-crystals.