A reverse micelle technique was used to prepare size-controlled tetrahedral micro- and nanocrystals of the coordination network [Ru(bpy)3][NaCr(ox)3], ox = oxalate, bpy = 2,2'-bipyridine. After laser excitation at 532 nm, the 2E emission of Cr(III) indicates an efficient directional energy transfer from the chromophores located in the core of the nanocrystals towards the ones closer or at the surface. The functionalization of the nanocrystals surface by direct chemical grafting of energy acceptors in form of encapsulated lanthanides complexes ([Ln(hafc)3dig], Ln3+ = Yb3+, Er3+, Eu3+, dig = diglyme) decreases the inhomogeneous width of the R-lines. The presence of the lanthanides transitions 4I13/2 → 4I15/2, 4I9/4 → 4I15/2 and 2F5/2 → 2F7/2 for Erbium and Ytterbium in the functionalized nanocrystals indicates down-conversion of the excitation energy. These results were evidenced by high-resolution absorption and emission spectroscopy.