CHARACTERIZATION AND OPTICAL PROPERTIES OF CDS:CU NANOCRYSTALS PREPARED BY CHEMICAL SYNTHESIS. O. Portillo-Moreno1a, J. Martínez1b* , R. Lozada-Morales1c, H. Lima-Lima1a, G. Juárez2a, O. Zelaya-Angel2b, E. Rosendo1b, H. Juárez1b, and T. Díaz1b Benemérita Universidad Autónoma de Puebla. aFacultad de Ciencias Químicas, bCIDSICUAP, cFacultad de Ciencias Físico-Matemáticas. Av. 14 sur y Av. San Claudio, Col. San Manuel. Puebla, México 2 Centro de Investigación y de Estudios Avanzados. aDepartamento de Ingeniería Eléctrica, b Departamento de Física. P.O. Box 14-740, México 07360 D.F. 1 Abstract CdS:Cu nanocrystalline films were prepared by chemical bath on glass substrates at 80°C of deposition temperature (Td). Different Cu-doping levels were obtained by changing the volume of the Cu-reagent-solution into the CdS growing solution. The Cudoping was carried out adding small volumes of an aqueous solution of Cu(NO3)2 to the aqueous CdS growing solution. X-ray diffraction (XRD) and optical absorption (OA) measurements were carried out in order to characterize the material. From the XRD patterns it is concluded that the grains in undoped films grow in the Wurzite hexagonal phase, and in Cu-doped films they grow in the Zincblende cubic phase. The average grains size, located in the range 14-23 nm, was calculated by employing the Scherer’s formula. From OA spectra the forbidden energy band gap (Eg) was determined by using the (áhã) ! (E - hã )2 relation. As effect of doping, E shifts to lower values depending on the impurity level of the film.