Semiconducting properties of Tm doped Yb-ZnO films by spray pyrolysis Imane Chaki, Azzam Belayachi, Toufik El Bahraoui, Mohamed Regragui and Mohamed Abd-Lefdil Eur. Phys. J. Appl. Phys., 68 3 (2014) 30301 Published online: 25 November 2014 DOI: 10.1051/epjap/2014140371