As shown in the experimental part, CdSe quantum dots doped with cobalt ions prepared by thermal decomposition of organometallic precursors for both Cd2+ and Co2+ ions . Different concentrations of cobalt ions were mixed with cadmium stearate in the reaction mixture. Samples prepared using different concentrations of cobalt ions were characterized by TEM and XRD in order to determine the influence of doping on the magnetic and optical properties. Structural properties: models were studied for four samples prepared using different concentrations of cobalt versus Cd2+ concentration, representing 0, 2, 10, and 20%. All compared samples have the same size of approximately 4.2 nm and the same optical band gap of approximately 516 nm. The only difference is the doping ratio. Doping the crystal with impurities does not result in the appearance of new XRD peaks, but instead leads to gradual changes in the lattice parameters of the host material as the dopant concentration increases above the dilute limit. The shifts result from deformation induced when the dopant is incorporated into the periodic crystal lattice. The XRD pattern as shown in Figure (1) indicates that the prepared particles have Wurtizite (Wz) crystal structure for both undoped CdSe and doped Co2+ CdSe QD samples. In case of undoped CdSe QDs; where the Wz structure shows four distinct characteristics: the first at 2θ= 23.9° due to (100), and the three general characteristics appearing at 2θ=41.82, 45.71 and 49.98° due to (110), (103), and (112) reflections, respectively. In the case of CdSe doped with Co2+ at a doping ratio of 2%, the three most distinct features of the Wz structure are slightly shifted... to the center of the paper...tes" J. Amer. Chem. Soc. , 115, (1993) 8706.70. Peng, Z.A. and Peng, CdO as a precursor", J. Am. Chimica. Soc. 123 (2001) 18372. Mona B. Mohamed, Dino Tonti, Awas Al-Salman, Abdelkrim Chemseddine and Majed El-Chagui. "Synthesis of CdSe zinc mixture nanocrystals of high quality" J. Phys. Chemistry. 10, (2005) 1533,73. Bawendi, MG; "Chemistry and physics of semiconductor nanoclusters", Abstracts of Papers of the American Chemical Society, 208 (1994) 4-Inor.74 Emam, AN; Girgis, E.; Mostafa, A.A.; Guirguis, O.W.; Mohamed, M.B., "Magnetic doped semiconductor nanocrystals: new synthetic method and characterization of Co+2 ion-doped CdSe nanocrystals." 2012