Light Tape UK's History of Electroluminescence

Light Tape UK's "History of Electroluminescence" (Page 2)


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One of the key disadvantages of ELDs relative to liquid crystal displays (LCDs) was that until 1981 ELDs were not capable of displaying more than one colour. Even after 1981, colour ELDs were restricted to a limited range of colours (red, green, and yellow) until 1993 when a blue phosphor was discovered.

A SrS: Cu blue phosphor showing improved blue colour and efficiency was reported by Sey-Shing Sun of Planar in 1997. Planar demonstrated true white colour EL prototype displays using this blue phosphor in a SrS:Cu/ZnS:Mn multi-layer structure. The SrS:Cu phosphor will enable colour EL displays to be produced with a wider colour gamut.

Because of Planar's willingness to work with customers to adapt products for specific applications, it was able to command a price premium over the products of its main competitor, Sharp. By the late 1980s, Planar controlled over 90 percent of the world market for ELDs.

In spring 1995 Planar organized a consortium to develop the next generation of High Resolution and Colour TFEL Displays. This consortium was funded by the Department of Defense under the DARPA managed Technology Reinvestment Program (TRP). The total funding for the consortium was to be $30 million; half funded by the government and half by the consortium’s private firms. Other members of the consortium were: Allied Signal Aerospace, Computing Devices of Canada, Ltd., Advanced Technology Materials, Boeing, CVC Products, Georgia Tech Research Institute, Hewlett Packard, Honeywell, Lawrence Livermore National Laboratory, Los Alamos National Laboratory, Oregon State University, Positive Technologies and the University of Florida.[

In 1989, the Defense Advanced Research Projects Agency (DARPA) began to fund work on advanced displays as part of its High Definition Systems program. DARPA issued a Broad Area Announcement in that year and in subsequent years asking for proposals. Planar won one of the first grants from DARPA in 1990 and used the funds to set up a laboratory to develop colour ELDs.

Electroluminescent displays (ELDs) have a venerable history starting with the experiments of Captain Henry J. Round in 1907, O.V. Lossev in the Soviet Union, and Georges Destriau in France. Electroluminescence was mostly a scientific curiosity until the invention of thin film deposition techniques and the discovery that a sandwich of conductors, insulators and phosphors could result in a very efficient and long-lasting form of emissive display. ELDs were very important in the early days of the laptop computer industry and remained important in niche markets for military, medical and industrial equipment where high brightness, speed, contrast, and ruggedness are necessary.

The rise of the colour TFT LCD display forced the ELD producers to engage in research on colour ELDs with the result that by the mid 1990’s there were multicolour ELDs on the market and full-colour AMELs in development for microdisplays. By 1999 the ELD industry was limited to two major players: Planar and Sharp. Planar acquired its only European competitor, the Finlux Display Division of Lohja Oy, (Finland) in 1990. Sharp remains committed to competing in ELDs but its main focus is on liquid crystal displays. Most of the important research on ELDs remains within the corporate laboratories of Planar and Sharp, but several publicly funded research laboratories and consortia have also made important contributions to ELD technology.

The use of Electroluminescence has been limited until relatively recent times. The major obstacles to effective use of EL in the past have been: low light output, susceptibility to moisture and ultraviolet, colour shift, cost effective manufacture and short life.

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