Phosphor blends and backlight sources for liquid crystal...

Liquid crystal cells – elements and systems – Particular structure – Particular illumination

Reexamination Certificate

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C252S30140R, C252S30140P, C252S30140F, C252S30140H, C252S30160P, C252S30160F

Reexamination Certificate

active

06809781

ABSTRACT:

BACKGROUND OF INVENTION
The present invention relates generally to liquid crystal displays (“LCDs”) and backlight sources thereof. In particular, the present invention relates to phosphor blends for improved back lighting for color LCDs.
LCDs are widely used in the electronic industry on products ranging from cellular telephones, calculators, and watches to computers and information displays in automobiles. LCDs have many advantages over competing display technologies in areas such as size, cost, design, flexibility, reliability, and power consumption. These advantages make LCDs a popular choice for designers of electronic devices.
Liquid crystal material is characterized in that the light transmission through a thin layer of liquid crystal may be altered by applying an electric field to the material. This property is put to use in LCDs.
The essential component of an LCD consists of a thin liquid crystal material contained between two transparent plates, made of a material such as glass or an organic polymer. The inner surfaces of the transparent plates are provided with transparent electrodes that define the patterns, characters, or images to the displayed. The outer surfaces of the transparent plates are provided with polarizing lenses. When a voltage is applied across a pair of corresponding electrodes, light is blocked or permitted to pass through the assembly, depending on the relative orientation of the polarizing lenses. The location at which two electrodes overlap defines a pixel of the display. Such a display is termed a passive matrix display. In an active matrix display, a matrix of thin-film transistors (TFTs) are disposed on one transparent plate to serve as switching elements. A common electrode is provided on the second transparent plate. When a particular TFT is addressed to switch on, the liquid crystal material between that TFT and the common electrode becomes untwisted and allows light to pass through. A precisely controlled voltage can be supplied to the TFT to control the brightness at the pixel. Red, green, and blue color filters are disposed at adjacent pixels to create a different shade and color from each group of three TFTs when the chosen TFT is activated with a controlled level of voltage.
For display devices having high luminance, a source of backlight is provided behind the transparent plate opposite to the viewer. A miniature fluorescent lamp or a plurality of light-emitting diodes (“LEDs”) is typically used for this purpose. Such a light source that emits a broad spectrum, coupled with the color filters, allows for the transmission of a particular light color through the pixel. One white light-emitting backlight system disclosed in U.S. Pat. No. 5,982,092 consists of semiconductor LEDs emitting blue light or ultraviolet (“UV”) radiation in the wavelength range of 360-380 nm coupled with a layer of yellow light-emitting Y
3
Al
5
O
12
:Ce phosphor. such a system is not energy-efficient because the emission spectrum of Y
3
Al
5
O
12
:Ce is not concentrated in the wavelength ranges specific to the color filters that are typically used (about 440-460 nm, about 550-570 nm, and about 630-680 nm), as is shown in FIG.
1
.
Therefore, there is a continued need to provide more energy-efficient backlight systems for LCDs. It is also very desirable to provide phosphor blends for improved color LCDs.
SUMMARY OF INVENTION
The present invention provides phosphor compositions for backlight sources in LCDs. Such phosphor compositions offer improved utilization of energy by emitting visible light more intensely in the wavelength ranges of typical blue, green, and red color filters. The terms “light” and “electromagnetic radiation” are used interchangeably herein to mean electromagnetic radiation having wavelengths in the range from about 200 nm to about 770 nm.
A phosphor composition of the present invention comprises at least a phosphor emitting blue light, at least a phosphor emitting green light, and at least a phosphor emitting red light. The phosphor emitting blue light is selected from the group consisting of (Sr,Ca,Ba,Mg)
10
(PO
4
)
6
(F,Cl,Br,OH):Eu
2+
(hereinafter also called “SECA”); (Ba,Sr,Ca)MgAl
10
O
17
:Eu (hereinafter also called “BAM”); (Sr,Ca)
10
(PO
4
)
6
•nB
2
O
3
:Eu
2+
, wherein 0<n<1; 2 SrO•0.84 P
2
O
5
•0.16 B
2
O
3
:Eu
2+
; Sr
2
Si
3
O
8
•2 SrCl
2
:Eu
2+
; Ba
3
MgSi
2
O
8
:Eu
2+
; Sr
4
Al
14
O
25
:Eu
2+
(hereinafter also called “SAE”); BaAl
8
O
13
:Eu
2+
; and mixtures thereof. The phosphor emitting green light is selected from the group consisting of (Ba,Sr,Ca)MgAl
10
O
17
:Eu
2+
,Mn
2+
(hereinafter also called “BAMn”); (Ba,Sr,Ca)Al
2
O
4
:Eu
2
+; (Y,Gd,Lu,Sc,La)BO
3
:C
3+
,Tb
3+
; (Ba,Sr,Ca)
2
SiO
4
; Eu
2+
; (Ba,Sr,Ca)
2
(Mg,Zn)Si
2
O
7
:Eu
2+
; (Sr,Ca,Ba)(Al,Ga,In)
2
S
4
:Eu
2+
; (Y,Gd,Tb,La,Sm,Pr,Lu)
x
(Al,Ga,In)
y
O
12
:Ce
3+
, wherein x is in the range from about 2.8 to and including 3, and y is in the range from about 4.9 to about 5.1; (Sr,Ca,Ba,Mg,Zn)
2
P
2
O
7
:Eu
2+
, Mn
2+
(hereinafter also called “SPP”); (Ca,Sr,Ba,Mg)
10
(PO
4
)
6
(F,Cl,Br,OH): Eu
2+
,Mn
2+
(hereinafter also called “HALO”); (Ca,Sr,Ba)
8
(Mg,Zn)(SiO
4
)
4
(Cl,F)
2
:Eu
2+
,Mn
2+
(hereinafter also called “CASI”); and mixtures thereof. The phosphor emitting red light is selected from the group consisting of (Gd,Y,Lu,La)
2
O
3
:Eu
3+
,Bi
3+
; (Gd,Y,Lu,La)
2
O
2
S:Eu
3+
,Bi
3+
; (Gd,Y,Lu,La)VO
4
:Eu
3+
,Bi
3+
; SrS:Eu
2+
; SrY
2
S
4
:Eu
2+
; CaLa
2
S
4
:Ce
3+
; (Ca,Sr)S:Eu
2+
; 3.5 MgO•0.5 MgF
2
•GeO
2
:Mn
4+
(hereinafter also called “MFG”); (Ba,Sr,Ca)MgP
2
O
7
:Eu
2+
,Mn
2+
; and mixtures thereof.
In one aspect of the present invention, an LCD comprises a backlight source comprising at least a light source emitting in at least a range from about 300 nm to about 450 nm and a light-conversion phosphor composition comprising at least a phosphor emitting blue light, a phosphor emitting green light, and a phosphor emitting red light. The phosphor composition is disposed to receive electromagnetic radiation emitted by the light source and emits visible light.
In another aspect of the present invention, the phosphor composition is disposed between the light source and a layer of liquid crystal material of the LCD.
Other features and advantages of the present invention will be apparent from a perusal of the following detailed description of the invention and the accompanying drawings in which the same numerals refer to like elements.


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