Patent Grant
7452483
Electroluminescence is the emission of light under electric-field excitation. Based on this mechanism, electroluminescent (EL) lamps are finding an increasing number of applications in the field of flat panel displays due to the growing demand for consumer electronic products, e.g., cellular phones and portable computing devices. EL lamps also provide uniform light emission independent of viewing angle and they are insensitive to mechanical shock and vibration. They can be easily DC-driven at 1.5-9 volts by using inverters that generate AC voltages of about 100-300 V (peak-to-peak) at frequencies of 50 to 1000 Hz.
The two major EL lamp constructions are generally referred to as thin film and thick film. Thin-film EL lamps are made by depositing alternating thin layers of dielectric materials, phosphors and conductive oxides on a glass substrate using a vapor deposition technique such as CVD. Thick-film lamps are made by suspending powdered materials in resinous materials and then applying the materials in layers onto a plastic film using conventional screen printing techniques. Hence, the thick-film EL lamps can be thin, flexible and rugged thereby making them suitable for a wider range of lighting applications.
The phosphors available for thick-film EL lamps are primarily comprised of zinc sulfide that has been doped with various activators, e.g., Cu, Au, Ag, Mn, Br, I, and Cl. Examples of these phosphors are described in U.S. Pat. Nos. 5,009,808, 5,702,643, 6,090,311, and 5,643,496. Examples of commercial EL phosphors include: OSRAM SYLVANIA Type 813, a blue-emitting ZnS:Cu phosphor, OSRAM SYLVANIA Type 723, a blue-green emitting ZnS:Cu,Cl phosphor and OSRAM SYLVANIA Type 523, a yellow-orange emitting ZnS:Cu,Mn phosphor. Typically, the individual particles of the EL phosphors are encapsulated with an inorganic coating in order improve their resistance to moisture-induced degradation. Examples of such coatings are described in U.S. Pat. Nos. 5,220,243, 5,244,750, 6,309,700, and 6,064,150.
The brightest of the phosphors for thick-film EL lamps emit primarily in the blue to green spectral region at wavelengths from about 400 nm to about 550 nm. Because of this, the color palette available to manufacturers of EL lamps is relatively limited. EL phosphors have been combined with photoluminescent phosphors in order to produce a white light. Unlike EL phosphors, the photoluminescent phosphors are not stimulated by the electric field in an EL lamp. Instead, the photoluminescent phosphors are excited by the light emitted by the EL phosphor. These phosphors produce a visible light emission which when combined with the remaining emission from the EL phosphor makes a white light.
For example, Chinese Patent Publication No. CN 1340590A describes mixing blue- and blue-green emitting EL phosphors with a cerium-activated yttrium aluminum garnet phosphor Y3Al5O12:Ce, (YAG:Ce). The YAG:Ce phosphor is a photoluminescent phosphor that is excited by wavelengths emitted by the blue and blue-green EL phosphors. The yellow emission from the YAG:Ce phosphor together with the blue- or blue-green emission from the EL phosphor creates a white light. Other examples include U.S. patent application Ser. No. 11/164,153 which describes a white-emitting electroluminescent lamp that uses a phosphor blend comprising a blue- or blue-green emitting electroluminescent phosphor and an europium-activated alkaline earth phosphor having the general formula Sr1−xCaxS:Eu where 0≦x≦1, and U.S. patent application Ser. No. 10/711,682 which describes a high CRI electroluminescent lamp produced by combining a blue- or blue-green emitting EL phosphor with an europium-activated alkaline earth silicon nitride phosphor.
The present invention expands the color palette available to EL lamp manufacturers by providing a yellow-emitting phosphor blend for EL lamps. Preferably, the blend exhibits an x color coordinate from 0.220 to 0.350 and a y color coordinate from 0.450 to 0.475 when stimulated by an electric field. More particularly, it has been found that a green emission from an EL phosphor may be used to excite various red-emitting photoluminescent phosphors. By blending the phosphors and incorporating them into an EL lamp, the combined emission of the photoluminescent phosphor and the green-emitting EL phosphor produces a yellow light.
Preferably, the green-emitting EL phosphor is a copper-activated zinc sulfide (ZnS:Cu,Cl) phosphor that emits between 470 nm to 550 nm. Preferred photoluminescent phosphors are Sr1−xCaxS:Eu where 0≦×≦1 (herein referred to as (Sr,Ca)S:Eu) and (M1−xM′x)Si5N8:Eu where M and M′ are at least one of Ca, Sr, and Ba and 0≦×≦1. Preferably, the phosphors have a red emission having an x color coordinate from 0.570 to 0.695 and a y color coordinate from 0.325 to 0.430.
Preferably, the green-emitting EL phosphor comprises from 85 to 96 weight percent of the blend and the photoluminescent phosphor comprises from 4 to 15 weight percent of the blend. In a more preferred embodiment, the blend exhibits an x color coordinate from 0.235 to 0.335 and a y color coordinate from 0.460 to 0.465 when stimulated by an electric field.
For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims taken in conjunction with the above-described drawings.
The emission of a conventional green-emitting ZnS:Cu,Cl electroluminescent phosphor (e.g., OSRAM SYLVANIA Type 728) is shown in
Similarly, in
A green-emitting ZnS:Cu,Cl phosphor (OSRAM SYLVANIA Type 728) and a red-emitting (Sr,Ca)S:Eu phosphor where coated with a hydrolzyed trimethylaluminum (TMA) coating in accordance with U.S. Pat. No. 5,220,243. Several blends of these phosphors were prepared by adding various amounts of the phosphors to a plastic bottle and blending on a paint shaker for twenty minutes. The amount of the coated (Sr,Ca)S:Eu phosphor varied from 4 to 15% by weight. The remainder of the blend consisted of the coated green-emitting EL phosphor. Test lamps having a conventional thick-film construction were made with the phosphor blends and operated at 100V, 400 Hz. The results of the lamp tests are given in the Table. The x,y color coordinates referred to herein are for the 1931 Commission Internationale de I'Eclairage (CIE) Standard Observer (2°).
While there have been shown and described what are present considered to be the preferred embodiments of the invention, it will be apparent to those skilled in the art that various changes and modifications can be made herein without departing from the scope of the invention as defined by the appended claims.
This application is a continuation-in-part of copending application Ser. No. 11/164,153, filed Nov. 11, 2005, which is a continuation-in-part of application Ser. No. 10/711,682, filed Sep. 30, 2004, both of which are hereby incorporated by reference.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5009808 | Reilly et al. | Apr 1991 | A |
| 5156885 | Budd | Oct 1992 | A |
| 5220243 | Klinedinst et al. | Jun 1993 | A |
| 5244750 | Reilly et al. | Sep 1993 | A |
| 5643496 | Brese et al. | Jul 1997 | A |
| 5702643 | Reddy et al. | Dec 1997 | A |
| 6064150 | Klinedinst et al. | May 2000 | A |
| 6090311 | Brese et al. | Jul 2000 | A |
| 6309700 | Fan et al. | Oct 2001 | B1 |
| 6649946 | Bogner et al. | Nov 2003 | B2 |
| 6682663 | Botty et al. | Jan 2004 | B2 |
| 20040135504 | Tamaki et al. | Jul 2004 | A1 |
| 20050156496 | Takashima et al. | Jul 2005 | A1 |
| 20060066209 | Chau | Mar 2006 | A1 |
| 20060066221 | Belinski-Wolfe et al. | Mar 2006 | A1 |
| Number | Date | Country |
|---|---|---|
| 1340590 | Mar 2002 | CN |
| 1001660 | May 2000 | EP |
| 1605028 | Dec 2005 | EP |
| WO 0211173 | Feb 2002 | WO |
| WO2004081140 | Sep 2004 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20060261310 A1 | Nov 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11164153 | Nov 2005 | US |
| Child | 11462053 | US | |
| Parent | 10711682 | Sep 2004 | US |
| Child | 11164153 | US |
