Actually, there are a lot of scientific literature on the II-VI semiconductor material zinc oxide (ZnO) produced by researchers dedicated to the physical optical study in all the world, because the ZnO has singular and extraordinary physical and chemical properties: presents a wide direct band gap of 3.37 eV at room temperature [1] and has bonding energy of 60 meV that makes ZnO very apt for exciton-based applications [2] . However, such properties make to the ZnOa very versatile material ideal for working in conjunction with other materials. The ZnO has been studied in basic and technological applications: fabrication of the follow devices: electro-optic [3] , solar cells [4] , piezo-electric [5] , magnetic [6] , gas sensors [7] , photoluminescent [8] , etc. The ZnO can be synthesized using various methods, such as: magnetron sputtering [9] , chemical vapor deposition (CVD) [10] , Co-presipitation [11] , metalorganic [12] and solution combustion (SC) technique [13] : this last method is very fast, less expensive, easier variables deposit control, very efficient and highly reproducible. In this work we used SC as synthesis method. In other hand, the Cu atoms incorporation into the crystalline lattice of the ZnO leads to change or improvement in some properties of the ZnO material such as: band gap tailored, electric, magnetic, electronic, thermoluminescent, surface defects control, structural, and photoluminescent [14] [15] [16] [17] . Furthermore, the Cu ion has been used to quenching the Eu³⁺ PL in glasses and ZnO matrix [18] [19] . In addition, specifically, the ZnO can be doped with various elements of the periodical table (lanthanides, earth rare, metals, phosphorous, etc.) for changing the ZnO intrinsic PL emission spectra as well as its emission intensity [20] [21] [22] [23] . Between the ZnO dopants the most prominent is the cerium atom (Ce³⁺), the first element of the lanthanide series due to its high PL emission efficiency and wide versatility: according to the studies realized by various researchers [24] - [29] , from your experimental results the authors show that the Ce³⁺ doped ZnO can presents anomalous PL emission spectra: from the UV radiation until the red color emissions; this multiple color PL emission is attributed to the Ce³⁺ ion and also depend of the excitation radiation of illumination. In this work, pure ZnO, Ce³⁺ doped ZnO and Cu²⁺ + Ce³⁺ co-doped ZnO solution powders were synthesized by a solution combustion technique. The ZnO/Cu²⁺ + Ce³⁺ compound was synthesized as a function of the Cu²⁺ ion concentration in %wt. maintaining constant the Ce³⁺ ion concentration at 3% wt. The three type’s samples were annealed at 900˚C by 24 h. Structurally the samples were characterized by means of X-ray diffraction (XRD) technique. Your photoluminescence properties were studied by measuring its PL under an excitation wavelength of 378 nm at room temperature.

The chemical synthesis technique by solution combustion is possible thanks to the development of a chemical reaction of oxidation-reduction (REDOX) between an oxidizer agent and a fuel, the reaction is highly exothermic (1200˚C) [30] producing oxides metallic, water vapor, carbon-dioxide and nitrogen molecular. In our experiment zinc nitrate hexahydrate (Zn(NO₃)₂∙6H₂O) was used as oxidizer agent and urea (5H NCONH)as fuel. In the follow chemical REDOX reaction:

The Equation (1) is the stoichiometric form of the REDOX reaction obtained with a equivalence ratio value of unity (i.e. f = O/F = 1) where O and F are the total oxidizing and total reduction valences of the agents and the energy released by the combustion is at maximum [30] . Using the Equation (1), intrinsic ZnO, Ce³⁺ doped ZnO and Cu²⁺ + Ce³⁺ co-doped ZnO solid solution powders were synthesized and after annealed at 900˚C by 24 h. The source of the dopants Cu²⁺ and Ce³⁺ were copper chloride (CuCl₂) and cerium oxide Ce₂O₃ respectively. The Ce³⁺ ion concentration was fixed at 3%wt, while the Cu²⁺ ion concentration takes the values of 0%wt, 1%wt, 2%wt, 3%wt, 10%wt and 20%wt. The pure ZnO, ZnO/Ce³⁺, and ZnO/Cu²⁺ + Ce³⁺ samples thus obtained were structurally characterized by X-ray diffraction (XRD) technique using a Philips PW 1800 diffractometer with Cu kα radiation (1.5406 Å), the morphology of the powders samples was recorded using a scanning electron microscopy (SEM) JEOL JSM 840. The PL study was realized using a spectrofluorometer Fluoro Max-P that uses a xenon lamp.

In this work the effects caused by the Cu²⁺ ion on the structural and optical properties of co-doped compounds type ZnO: Cu²⁺ + Ce³⁺ synthesized by a solution combustion method have been investigated. It is found that the copper ion presence does not change the ZnO crystalline structure. The PL emission spectra consist of four relevant peaks: two peaks centered in the blue color region attributed to an electric-dipole-allowed; and the other two peaks centered in the red color region due to radiative recombination between donoroxygen vacancies defects and the acceptors Cu²⁺ impurity. However, it is concluded that the Cu²⁺ ion introduction into the ZnO crystalline lattice quenching the UV Pl of the ZnO semiconductor matrix caused by a non-radiative-recombination Auger effect; this result can be technologically used to fabric devices photoluminescent with ZnO matrix without UV emission.

The authors wish to thank to Dr. Ciro Falcony (IPN), Adriana Tejeda (IIM) for the XRD measurements, to Omar Novelo Peralta (IIM) for his SEM study, to M.A. Canseco Martinez (IIM) for their chemical analysis.

López-Romero, S., Quiroz Jiménez, M.J., García-Hipólito, M. and Chávez-Ramírez, J. (2017) Influenza of the Cu Ion on the Structural and Optical Properties in Cu + Ce Co-Doped ZnO Compounds. World Journal of Condensed Matter Physics, 7, 47-55. https://doi.org/10.4236/wjcmp.2017.72005