Band-Gap Energy Dependence of Emission Spectra in Rare Earth-Doped Zn(1-x)CdxS Thin Film Electroluminescent Devices

Electroluminescence has been measured for Zn(1-x)Cd x S thin films doped with rare earth ions. The ZnS thin film doped with the Pr ion shows the 495 and 658 nm emissions due to the transitions from the 3P0 to 3H4 and 3F2 levels, respectively. With increasing value of X, the emission from the 3P0 level vanished and 618 nm emission arose from the transition of 1D2→3H4. The reason for this change may be related to the band-gap energy of the host lattice. From these experimental results, it is concluded that the excitation process of the rare earth ions involves the energy transfer from the host lattice for the Zn(1-x)Cd x S electroluminescent devices. In addition, the transition around 800 nm emission for the Tm3+ ion is also discussed.