Phosphors for light generation from light emitting...

Details Phosphors for light generation from light emitting... Phosphors for light generation from light emitting...

2000-05-26

2001-07-03

Tran, Minh Loan (Department: 2826)

Active solid-state devices (e.g., transistors, solid-state diode

Incoherent light emitter structure

Plural light emitting devices

C257S098000, C257S099000, C257S100000, C313S501000, C313S503000

Reexamination Certificate

active

06255670

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to phosphors. In particular, the invention relates to phosphor compositions for light emitting diodes and laser diodes.
BACKGROUND OF THE INVENTION
Semiconductor light emitters are well known in the art. Semiconductor light emitters include light emitting diodes (LEDs) and laser diodes. LEDs are devices of choice for many display applications because of the advantages LEDs have over other light sources. These advantages include a relatively small size, a low operating current, a naturally colored light, a low power consumption, a long life, a maintained high efficiency (power in versus light output), an acceptable dispersal of light, and a relatively low cost of manufacture compared to other light sources.
Applications for LEDs include the replacement of light sources, such as incandescent lamps, especially where a colored light source is desired. LEDs are often used as display lights, warning lights and indicating lights. LEDs are advantageous in such applications, because they emit light in a relatively narrow range of wavelengths corresponding to a particular color. LEDs have not conventionally been used for lighting applications where a bright white light is needed, due to their inherent color.
Recently, blue emitting LEDs have been used to provide a whitish light, for example as backlights in liquid crystal displays and as replacements for small conventional lamps and fluorescent lamps. As discussed in chapter 10.4 of “The Blue Laser Diode” by S. Nakamura et al., pages 216-221 (Springer 1997), incorporated herein by reference, white light LEDs can be fabricated by forming a ceramic phosphor layer on the output surface of a blue emitting semiconductor LED. The blue LED is an InGaN single quantum well LED, and the phosphor is a cerium doped yttrium aluminum garnet Y
3
Al
5
O
2
:Ce
3+
(“YAG:Ce”). The blue light emitted by the LED excites the phosphor, causing it to emit yellow light. The blue light emitted by the LED is transmitted through the phosphor and is mixed with the yellow light emitted by the phosphor. The viewer perceives the mixture of blue and yellow light as white light.
However, the blue LED—YAG:Ce phosphor white light illumination system suffers from the following disadvantages. The blue LED—YAG:Ce phosphor system produces white light with a high color temperature ranging from 6000 K to 8000 K, which is comparable to sunlight, and a typical color rendering index (CRI) of about 70 to 75. While the blue LED—YAG:Ce phosphor illumination system with a relatively high color temperature and a relatively low CRI is acceptable to customers in the far east lighting markets, the customers in the North American markets generally prefer an illumination system with a lower color temperature, while the customers European markets generally prefer an illumination system with a high CRI. For example, North American customers generally prefer systems with color temperatures between 3000 K and 4100 K, while European customers generally prefer systems with a CRI above 90.
The color temperature of a light source refers to the temperature of a blackbody source having the closest color match to the light source in question. Generally, as the color temperature increases, the light becomes more blue. As the color temperature decreases, the light appears more red. The color rendering index (CRI) is a measure of the degree of distortion in the apparent colors of a set of standard pigments when measured with the light source in question as opposed to a standard light source. Light sources having a relatively continuous output spectrum, such as incandescent lamps, typically have a high CRI, e.g. equal to or near 100. Light sources having a multi-line output spectrum, such as high pressure discharge lamps, typically have a CRI ranging from about 50 to 80.
Another disadvantage of the above LED lamp relates to the efficiency of the lamp. The lumens per watt (LPW) of the above-described LED is in a range of about 5 LPW to about 10 LPW. LED radiation at about 5 LPW to about 10 LPW with a CRI of about 70-75 may not be acceptable for many lighting applications. For example, many lighting applications require a LPW that is 15 LPW or more, with a CRI maintained at or above 85. Known LED light sources do not provide a single LED with a sufficient LPW and CRI for most generalized lighting applications, especially for white light.
Therefore, a semiconductor light source that produces a bright white light is needed. Also, efficient green light emitting phosphors are needed for phosphor conversion material blends to produce a bright white light.
SUMMARY OF THE INVENTION
Accordingly, the invention provides light source that overcomes the above-noted deficiencies. The invention also provides phosphors that produce light that when combined with other lights produce a bright white light.
In accordance with one embodiment of the invention, a phosphor Ca
8
Mg(SiO
4
)
4
Cl
2
:Eu
2+
,Mn
2+
absorbs ultraviolet radiation from a light emitting diode and converts the radiation into visible light.
In another embodiment of the invention a phosphor, Y
2
O
3
:Eu
3+
,Bi
3+
absorbs ultraviolet radiation from a light emitting diode and converts the radiation into visible light.
In a further embodiment of the invention a phosphor A
2
DSi
2
O
7
:Eu
2+
, wherein A is one or more of Ba, Ca, Sr, and D is Mg and Zn, absorbs ultraviolet radiation from a light emitting diode and converts the radiation into visible light.
Yet another embodiment of the invention is a phosphor conversion material blend comprising green, red and blue phosphors that absorb ultraviolet radiation from a light emitting diode, and convert the radiation into visible bright white light. The green phosphor comprises Ca
8
Mg(SiO
4
)
4
Cl
2
:Eu
2+
,Mn
2+
, the red phosphor comprises Y
2
O
3
:Eu
3+
,Bi
3+
, and the blue phosphor comprises known blue phosphors, such as (Sr,Ba,Ca)
5
(PO
4
)
3
Cl:Eu
2+
and BaMg
2
Al
16
O
27
:Eu
2+
.
Furthermore, another embodiment of the invention provides an LED including a phosphor comprising Ca
8
Mg(SiO
4
)
4
Cl
2
:Eu
2+
,Mn
2+
capable of absorbing ultraviolet radiation and converting the radiation into a green visible light.
In a yet further embodiment of the invention, an LED includes a phosphor comprising (Sr,Ba,Ca)
5
(PO
4
)
3
Cl:Eu
2+
and BaMg
2
Al
16
O
27
:Eu
2+
capable of absorbing ultraviolet radiation and converting the radiation into blue visible light.
In a further embodiment of the invention, an LED includes a phosphor comprising Y
2
O
3
:Eu
3+
,Bi
3+
capable of absorbing ultraviolet radiation and converting the radiation into red visible light.
In a still further embodiment of the invention, an LED includes a phosphor comprising A
2
DSi
2
O
7
:Eu
2+
, where A is one or more of Ba, Ca, Sr, and D is Mg and Zn, capable of absorbing ultraviolet radiation and converting the radiation into green visible light.
Another embodiment of the invention provides an LED with a phosphor conversion material blend that comprises Ca
8
Mg(SiO
4
)
4
Cl
2
:Eu
2+
,Mn
2+
, Y
2
O
3
:Eu
3+
,Bi
3+
, and (Sr,Ba,Ca)
5
(PO
4
)
3
Cl:Eu
2+
and BaMg
2
Al
16
O
27
:Eu
2+
to absorb ultraviolet radiation from a light emitting diode and convert the radiation into visible bright white light.
According to another embodiment of the invention, a lighting apparatus is provided which comprises a semiconductor light emitting element such as an LED or a laser diode, a red emitting phosphor, a blue emitting phosphor, and the green emitting phosphor A
2
DSi
2
O
7
:Eu
2+
, where A is one or more of Ba, Ca, Sr, and D is Mg and Zn.
According to another embodiment of the invention, a lamp is provided which comprises a laser diode which emits radiation, a transmissive body fixed to the laser diode through which radiation from the laser diode propagates, and at least one phosphor fixed with respect to the transmissive body which converts the radiation to radiation of a different wavel

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