Improvement of Luminescence and Photocatalytic Performance of ZnO:Eu\({}^{3+}\) Nanocrystals Activated by Na\({}^{+}\) Ions  
Wiem Bouslama  
Laboratory of Composite Materials and Clay Minerals, National Center of Research in Material Sciences, Hammam-Lif 2050, Tunisia; [EMAIL_ADDRESS] (W.B. ); [EMAIL_ADDRESS] (E.S.) Laboratory of Chemistry for Inorganic/Organic Hybrid Functionalized Materials, School of Chemistry and Chemical Engineering, Anhui University, Hefei 230601, China; [EMAIL_ADDRESS] (R.N. ); [EMAIL_ADDRESS] (J-M.S.) Graduate School of Science, Nagoya University, 2-24-16 Furo-Cho, Chikusa-ku, Nagoya 464-8602, Aichi, Japan; [EMAIL_ADDRESS]-u.acj  
[PERSON] Srasrasra  
Laboratory of Composite Materials and Clay Minerals, National Center of Research in Material Sciences, Hammam-Lif 2050, Tunisia; [EMAIL_ADDRESS] (W.B. ); [EMAIL_ADDRESS] (E.S.) Laboratory of Chemistry for Inorganic/Organic Hybrid Functionalized Materials, School of Chemistry and Chemical Engineering, Anhui University, Hefei 230601, China; [EMAIL_ADDRESS] (R.N. ); [EMAIL_ADDRESS] (J-M.S.) Graduate School of Science, Nagoya University, 2-24-16 Furo-Cho, Chikusa-ku, Nagoya 464-8602, Aichi, Japan; [EMAIL_ADDRESS]-u.acj  
Habib Elhouichet  
Laboratory of Composite Materials and Clay Minerals, National Center of Research in Material Sciences, Hammam-Lif 2050, Tunisia; [EMAIL_ADDRESS] (W.B. ); [EMAIL_ADDRESS] (E.S.) Laboratory of Chemistry for Inorganic/Organic Hybrid Functionalized Materials, School of Chemistry and Chemical Engineering, Anhui University, Hefei 230601, China; [EMAIL_ADDRESS] (R.N. ); jiming@ahu. Nanocrystalline ZnO is one of the promising hosts for rare earth and metallic ions since it has a direct large band gap (3.37 eV), high exciton binding energy (60 meV), and high thermal and chemical stabilities. Further, the wide luminescence spectrum of ZnO [6] (covering a part of the UV and most of the visible region) overlaps with the Eu\({}^{3+}\) absorption bands [7], which can generate further processes of excitation transfer. Moreover, as an effective strategy to improve ZnO photocatalytic activity, doping with metallic ions has attracted significant attention because these ions could efficiently trap the photoinduced charge carriers [8; 9]. Previously, we have shown a large enhancement of visible light absorption by doping ZnO NCs with Na\({}^{+}\) ions [10], which was due to the formation of an acceptor level related to NaZn species, as revealed from a photoluminescence (PL) study. Thereafter, the photocatalytic activities were evaluated. As a result, we have shown that doping ZnO with Na is a simple and efficient way to achieve a high photodegradation of organic dyes in water. On the other hand, several studies conducted thus far have focused on the doping of ZnO with rare earth (RE) ions [11; 12]. As known, Eu\({}^{3+}\) is the most-studied RE ion thanks to its efficient red emission, which is solicited in many applications. In addition, Eu\({}^{3+}\) doping can decrease the optical band gap and improve light absorption in the entire visible region for maximum utilization of the solar spectrum [13]. Furthermore, the longer charge carrier lifetime relative to Eu\({}^{3+}\) ions is promising for the application of ZnO-Eu\({}^{3+}\) as an efficient photocatalyst under sunlight irradiation. However, the presence of an activator such as Na\({}^{+}\) in the ZnO:Eu host can enhance the red luminescence of Eu\({}^{3+}\) and extend the charge carrier lifetime, which is beneficial for the photodegradation of dyes in water. In fact, alkali metals (Na\({}^{+}\), Li\({}^{+}\) and K\({}^{+}\)), which are widely used as sensitizers, can modify the environment around Eu\({}^{3+}\) ions and transfer electrons by interactions since they occupy both substitutional or interstitial sites and create oxygen vacancies [10]. [PERSON] et al. [2] showed the successful insertion of Sm\({}^{3+}\) ions into the ZnO crystal lattice and both PL features and photocatalytic efficiency were optimized for 1.5% doping.