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

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Abstract
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.