Electroluminescence of ZnS Lumocen Devices Containing Rare-Earth and Transition-Metal Fluorides

ZnS LUMOCEN (luminescence from molecular centers) films typically 2000-Å thick doped with rare-earth and transition-metal fluorides have been fabricated by vacuum coevaporation. Details of the fabrication techniques are presented for the 12 fluorides studied: PrF3, NdF3, SmF3, EuF3, TbF3, DyF3, HoF3, ErF3, TmF3, YbF3, CrF3, and MnF2. Concentration dependence of the brightness has been investigated for the ZnS/TbF3 device, the maximum occurring at 1.8 at.% Tb. Studies of brightness as a function of input power indicate that the ZnS/TbF3 device is the brightest with 50 foot-lamberts readily obtained. The power efficiency for ZnS:TbF3 is about 10−4. Emission spectra of the devices have been measured from 0.35 to 1.1 μ and related to known energy level schemes where possible. The intensity distributions of the spectra generally differ from those obtained by doping ZnS with the bare ions; the ZnS:CrF3 device yields a spectrum radically different from any Cr3+ luminescence previously investigated.