Patent Grant
7749405
This invention generally relates to electroluminescent (EL) lamps and phosphors, and, more particularly, to electroluminescent lamps for generating white light.
Electroluminescence is the emission of light under electric-field excitation. Based on this mechanism, 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. 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.
For signage and backlighting involving multi-color informational displays, it is important to be able to generate a white light with a high color rendering index (CRI). However, the brightest electroluminescent phosphors emit primarily in the blue to green spectral region at wavelengths from about 400 nm to about 550 nm. This makes it difficult to obtain a high CRI, white emission with EL lamps especially since a satisfactory red-emitting electroluminescent phosphor for thick-film EL lamps has yet to be developed.
A white-emitting electroluminescent lamp has been developed using 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, (herein referred to as (Sr,Ca)S:Eu). In the present invention, the (Sr,Ca)S:Eu functions as a photoluminescent phosphor by converting some of the blue- or blue-green light emitted by the electroluminescent phosphor into a red emission. The combined emissions of the electroluminescent phosphor and the (Sr,Ca)S:Eu phosphor produces an overall white emission from the lamp. In terms of CIE x,y color coordinates, white light may be generally defined as the central and generally ellipsoidal region of the CIE chromaticity diagram (also known as a Kelly Chart) shown in
The (Sr,Ca)S:Eu phosphor may be co-doped with another activator such as samarium ((Sr,Ca)S:Eu,Sm). A preferred (Sr,Ca)S:Eu phosphor contains from 0 to about 2 weight percent (wt. %) Ca. Preferably, the amount of (Sr,Ca)S:Eu phosphor in the phosphor blend is from about 5 to about 60 weight percent, and more preferably from about 5 to about 20 weight percent. The electroluminescent phosphor is preferably a ZnS:Cu electroluminescent phosphor and may contain other co-activators such as chlorine and gold. Preferably, the electroluminescent phosphor emits primarily between about 400 nm to about 550 nm and the (Sr,Ca)S:Eu phosphor emits primarily between about 580 nm to about 730 nm. In addition, it is preferred to provide the particles of the (Sr,Ca)S:Eu phosphor with a protective coating like the protective coatings applied to EL phosphors. In particular, it is preferred to apply the hydrolyzed trimethylaluminum (TMA) coating described in U.S. Pat. No. 5,220,243.
The white-emitting electroluminescent lamp made with the phosphor blend preferably has an CIE x color coordinate of between about 0.245 and about 0.320 and a y color coordinate of between about 0.300 and about 0.370. More preferably, the x color coordinate is between about 0.250 and about 0.260 and the y color coordinate is between about 0.330 and about 0.370. The lamp exhibits a CRI of at least about 75 and more preferably at least about 80. The blend ratio may have to be adjusted depending on the operating conditions of the lamp since this can affect the intensity of the light emitted by the EL phosphor.
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.
Referring to
Several phosphor blends were prepared by adding the appropriate amounts of the phosphors to a plastic bottle and blending on a paint shaker for twenty minutes. Two electroluminescent (EL) phosphors were used: OSRAM SYLVANIA Inc.'s GlacierGlo® types GG65 (blue-emitting) and GG25 (blue-green emitting). The amount of the (Sr,Ca)S:Eu phosphor was varied from 10 to 50% by weight (wt. %). The remainder of the blend consisted of types GG65 and GG25, or a combination thereof. The amount of the GG65 EL phosphor ranged from 0 to 60% and the amount of the GG25 EL phosphor ranged from 0 to 70% by weight. The EL phosphors and the (Sr,Ca)S:Eu phosphor had a protective coating of hydrolyzed TMA on the individual phosphor particles. The phosphor blends were incorporated into thick-film EL lamps and operated generally at 100V, 400 Hz.
A series of six samples were prepared by blending 30, 40 or 50 wt. % of a (Sr,Ca)S:Eu phosphor containing 1.3 wt. % Ca with either type GG65 or GG25 EL phosphor. The lamp data is given in Table 1. Lamp luminance was measured at 24 and 100 hours. The color coordinates of the 40 wt. % (Sr,Ca)S:Eu with GG65 are very close to the coordinates for Daylight White (0.333, 0.333).
Three samples were prepared by blending 10, 20 and 30 wt. % of a (Sr,Ca)S:Eu phosphor containing 1.3 wt. % Ca with a 50/50 blend of GG65 and GG25 by weight. The lamp results are given in Table 2. The lamp resulting from the blend of 10 wt. % (Sr,Ca)S:Eu with the EL blend resulted in a preferred white emitting lamp.
Two more series of blends were prepared by blending 10 wt. % of a (Sr,Ca)S:Eu phosphor containing 1.3 wt. % Ca with different ratios of types GG65 and GG25, 30/70 to 60/40 by weight, respectively. The lamp results are given in Table 3. The lamp produced using the 40/60 ratio produced a lamp that was white at both low and high frequencies.
While there has been shown and described what are at the present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein 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. 10/711,682, filed Sep. 30, 2004 which is 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 |
| 6153123 | Hampden-Smith et al. | Nov 2000 | A |
| 6309700 | Fan et al. | Oct 2001 | B1 |
| 6580224 | Ishii et al. | Jun 2003 | B2 |
| 6649946 | Bogner et al. | Nov 2003 | B2 |
| 6682663 | Botty et al. | Jan 2004 | B2 |
| 7452483 | Belinski-Wolfe et al. | Nov 2008 | B2 |
| 20010008363 | Sanghera et al. | Jul 2001 | A1 |
| 20030020101 | Bogner et al. | Jan 2003 | A1 |
| 20040135504 | Tamaki et al. | Jul 2004 | A1 |
| 20040227705 | Fujimoto et al. | Nov 2004 | A1 |
| 20050156496 | Takashima et al. | Jul 2005 | A1 |
| 20060066209 | Chau | Mar 2006 | A1 |
| Number | Date | Country |
|---|---|---|
| 1340590 | Mar 2002 | CN |
| 200510107656.4 | Sep 2005 | CN |
| 1001660 | May 2000 | EP |
| 1 104 799 | Jun 2001 | EP |
| 1 371 711 | Jun 2003 | EP |
| 1 433 831 | Jun 2004 | EP |
| 1 447 854 | Aug 2004 | EP |
| 05019930.6 | Sep 2005 | EP |
| 1605028 | Dec 2005 | EP |
| 06019597.1 | Sep 2006 | EP |
| 07011710.6 | Jun 2007 | EP |
| 01-302691 | Dec 1989 | JP |
| 2005-146190 | Jun 2005 | JP |
| 1098912006 | Nov 2006 | KR |
| WO 0033390 | Jun 2000 | WO |
| WO 0169982 | Sep 2001 | WO |
| WO 0211173 | Feb 2002 | WO |
| WO 03042327 | May 2003 | WO |
| WO 03080764 | Oct 2003 | WO |
| WO 2004081140 | Sep 2004 | WO |
| WO 2005029596 | Mar 2005 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20060066221 A1 | Mar 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10711682 | Sep 2004 | US |
| Child | 11164153 | US |
