**13. Sintering enhances thin film electroluminescence**

(ZnxCd1-x)S phosphors are of considerable interest because of their use as window material in solar cells. While powder phosphors were prepared by heating at 9000C in argon atmosphere, thin films (15-25 µm) were obtained by painting uniformly the mixture of phosphor powder along with 30% of CdCl2 and 65% propylene glycol on SnO2 substrate, drying in air at 1200C for 2h and then sintering at 6250C in N2 atmosphere for 30 min. CdCl2 is used as a sintering aid in the preparation of thin films of (ZnxCd1-x)S. During sintering Zn is gradually replaced by Cd through the reaction ZnS + CdCl2 ZnCl2 + CdS. This is confirmed by the red shift in the optical absorption edge of thin film when compared to that of powder phosphor. In sintered films new centres are created which increases the luminescence efficiency and emission occurs in green, yellow-orange and red regions as against only yellow-orange emission in (Zn,Cd)S:Mn,Sm phosphors. While the 525 nm emission band was interpreted as due to free to bound transition from conduction band and acceptor band, the 625 nm emission band was attributed to the radiative recombination of electrons from the donor and acceptor levels. Excitation from Sm3+ ion can be transferred to donor-acceptor pair which leads to enhanced emission at 625 nm. In addition, new traps (donor levels) are created in ZnS type phosphors containing Cl as co-activator when Zn was gradually replaced by Cd. Moreover, during sintering, Zn vacancies (VZn) are created which act as deep acceptors.
