AC TFEL device having a white light emitting multilayer phosphor

• US 5,598,059 A
• Filed: 04/19/1995
• Issued: 01/28/1997
• Est. Priority Date: 04/28/1994
• Status: Expired due to Term

• Current Assignee: Beneq Oy (Qingdao Sifang SRI & Intellectual Co., Ltd.)
• Original Assignee: Planar Systems Incorporated (Leyard Optoelectronic Co., Ltd.)
• Inventors: Sun, Sey-Shing, Tuenge, Richard T.
• Primary Examiner(s): Horabik, Michael
• Assistant Examiner(s): DAY, MICHAEL HENRY
• Application Number:
  US08/424,222
• Time in Patent Office: 650 Days
• Field of Search: 313/506, 313/503, 313/512, 313/509
• US Class Current: 313/509
• CPC Class Codes: C09K 11/574 with zinc or cadmium
• CPC Class Codes: C09K 11/7718 with alkaline earth metals
• CPC Class Codes: H05B 33/10 Apparatus or processes specially adapted to the manufacture of electroluminescent light sources
• CPC Class Codes: H05B 33/14 characterised by the chemical or physical composition or the arrangement of the electroluminescent material , or by the simultaneous addition of the electroluminescent material in or onto the light source
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps

Abstract

An AC thin film electroluminescent (TFEL) device includes a multilayer phosphor for emitting white light having improved emission intensity in the blue region of the spectrum. The multilayer stack consists of an inverted structure thin film stack having a red light emitting manganese doped zinc sulfide (ZnS:Mn) layer disposed on a first insulating layer; a blue-green light emitting cerium doped strontium sulfide (SrS:Ce) layer disposed on the red light emitting layer; and a blue light emitting cerium activated thiogallate phosphor (Sr_x Ca_1-x Ga₂ S₄ :Ce) layer disposed on the blue-green light emitting layer. The manganese doped zinc sulfide layer acts as a nucleating layer that lowers the threshold voltage, and the cerium activated thiogallate phosphor layer provides a moisture barrier for the hydroscopic cerium doped strontium sulfide layer. The white light from the multilayer phosphor can be appropriately filtered to produce any desired color.

Claims

1. An AC thin film electroluminescent (TFEL) device including a plurality of phosphor layers for forming a white light-emitting phosphor comprising:

(a) a bottom substrate;

(b) a first electrode layer deposited on the bottom substrate;

(c) a first insulating layer deposited on the first electrode layer;

(d) a red light-emitting phosphor layer comprising a ZnS;

Mn layer deposited on the first insulating layer;

(e) a blue green light-emitting phosphor layer comprising an SrS;

Ce layer deposited on the red light-emitting phosphor layer;

(f) a blue light-emitting phosphor layer comprising a Sr_x Ca_1-x Ga₂ S₄ ;

Ce layer, where 1≧

x≧

0, deposited on the blue green layer;

(g) a transparent second insulating layer placed atop the blue light-emitting phosphor layer; and

(h) a transparent second electrode layer deposited on the transparent second insulating layer.

2. The TFEL device of claim 1 wherein the ZnS:

Mn layer has a thickness of between 150 and 300 nm, the SrS;

Ce layer has a thickness of between 600 and 1200 nm, and the Sr_x Ca_1-x Ga₂ S₄ ;

Ce layer has a thickness of between 200 and 400 nm.

3. The AC TFEL device of claim 2 wherein the ZnS:

Mn layer, the SrS;

Ce layer and the Sr_x Ca_1-x Ga₂ S₄ ;

Ce layer are all sputtered phosphor layers.

4. The AC TFEL device of claim 1 wherein x=0.5.

5. The AC TFEL device of claim 1 wherein x=0.