Multi-source reactive deposition process for the preparation of blue light emitting phosphor layers for AC TFEL devices

A process for preparing a phosphor layer for an AC TFEL device comprising a transparent substrate, said phosphor layer having the chemical formula:

• M.sup.II M.sup.III.sub.2 X.sub.4 :RE
• where M.sup.II is a group II metal taken from the group magnesium, calcium, strontium and barium;
• M.sup.III is a group III metal taken from the group aluminum, gallium and indium;
• X is taken from the group selenium and sulfur;
• and RE comprises a rare earth activator dopant taken from the group cerium and europium, said process comprising the steps of:
• (a) placing each one of a plurality of deposition source chemicals comprising all of the elements of said phosphor layer in a respective effusion source having a selectively openable and closable shutter under an inert gas atmosphere and closing said shutter, wherein at least one of said deposition source chemicals of said group II metal or said group III metal is a compound;
• (b) thereafter placing said substrate and each said effusion source into a vacuum chamber and evacuating said vacuum chamber;
• (c) thereafter heating said substrate and each said effusion source to a respective elevated temperature to form a heated substrate and a chemical vapor in each said effusion source;
• (d) thereafter opening the shutter of each said effusion source for a vapor deposition time to allow said chemical vapor to form a phosphor layer on said heated substrate, and after said vapor deposition time, closing said shutter;
• and
• (e) thereafter cooling said substrate and venting said chamber to atmospheric pressure.