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Illumination system comprising a radiation source and a luminescent materialIllumination system comprising a radiation source and a luminescent material description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080093979, Illumination system comprising a radiation source and a luminescent material. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001]The present invention generally relates to an illumination system comprising a radiation source and a luminescent material comprising a phosphor. The invention also relates to a phosphor for use in such an illumination system. [0002]More particularly, the invention relates to an illumination system for the generation of specific, colored light, including white light, by luminescent down conversion and additive color mixing based on a blue to violet radiation-emitting diode in combination with a luminescent material comprising a phosphor. Today light emitting illumination systems comprising visible colored light emitting diodes as radiation sources are used single or in clusters for all kind of applications where rugged, compact, lightweight, high efficiency, long-life, low voltage sources of white or coloured illumination are needed. [0003]Such applications comprise inter alia illumination of small LCD displays in consumer products such as cellular phones, digital cameras and hand held computers. Pertinent uses include also status indicators on such products as computer monitors, stereo receivers, CD players, VCRs, and the like. Such indicators are also found in systems such as instrument panels in aircraft, trains, ships, cars, etc. [0004]Recently, various attempts have been made to make white light emitting illumination systems by using light-emitting diodes as radiation sources. When generating white light with an arrangement of red, green and blue light emitting diodes, the problem has been that white light of the desired tone cannot be generated owing to variations in the tone, luminance, and other properties of the individual light-emitting diodes. [0005]In order to solve this problem, various illumination system concepts have been developed for converting the color of light-emitted by light-emitting diodes by means of a luminescent material comprising a phosphor so as to provide a visible white light illumination. [0006]Such white light illumination systems have been based in particular either on the trichromatic (RGB) approach, i.e. mixing of three colors: namely red, green and blue, in which case the latter component of the output light may be provided by a phosphor or by the primary emission of the LED; or in a second, simplified solution, on the dichromatic (BY) approach, i.e. mixing of yellow and blue, in which case the yellow secondary component of the output light may be provided by a yellow phosphor and the blue component may be provided by a phosphor or by the primary emission of blue LEDs. [0007]One dichromatic (BY) approach, as disclosed, for example, in U.S. Pat. No. 5,998,925, uses a blue light emitting diode of InGaN semiconductor material combined with Y.sub.3Al.sub.5O.sub.12:Ce(YAG-Ce) as a phosphor. The YAG-Ce phosphor is coated on the InGaN LED, and a portion of the blue light emitted from the LED is converted into yellow light by the phosphor. Another portion of the blue light from the LED is transmitted through the phosphor. This system thus emits both blue light emitted from the LED and yellow light emitted from the phosphor. The mixture of blue and yellow emission bands is perceived as white light by an observer with a typical CRI in the middle 70 s and a color temperature Tc, that ranges from about 6000 K to about 8000 K. [0008]Although the method is advantageously simple and readily implemented, it is disadvantageously poor in color rendering at low color temperatures, resulting from a lack of red color content, and it suffers from a color-shifting problem as the operational current increases. Therefore it is not an ideal light source for illumination. [0009]One trichromatic RGB approach for manufacturing a white LED may be implemented by exploiting an ultraviolet-emitting UV LED for excitation of a set of phosphors. In this approach the visible part of the emitting spectrum is completely generated by phosphors. The UV radiation emitted by the LED excites the phosphors to emit red, green and blue light, and these tri-color lights are further mixed into white light. However, moving the pump source into the UV spectral range results in a reduced radiant efficacy because of increased energy losses in the conversion process. Besides, the packaging materials have an ageing problem due to the UV light damages. Therefore this is not a proper way to produce a white illumination source. [0010]Another trichromatic lamp approach for generating white light is disclosed in U.S. Pat. No. 6,686,691. The invention according to U.S. Pat. No. 6,686,691 relates to a tri-color lamp with specific red and green phosphors excitable by a common blue light emitting diode (LED). This arrangement provides a mixing of three light sources: light emitted from the two phosphors and unabsorbed light emitted from the LED. Power fractions of each of the light sources can be varied to achieve good color rendering. [0011]Yet, it is a general concern with phosphor-converted LED lamps using blue to violet emitting LEDs for excitation of phosphors that currently known phosphors have not been developed and optimized for such excitation. [0012]Currently known phosphors were developed and optimized for two major applications: (1) fluorescent lamps that utilize 254 nm UV radiation from a Hg discharge for excitation and (2) CRTs, where the RGB-phosphors are excited by an electron beam. [0013]This leads to a new challenge to be met by phosphors in phosphor- converted LEDs. [0014]It has been found in particular that the electro-optical efficiency of conventional red phosphors, for example Y.sub.2O.sub.3:Eu(III), as mentioned in US2004/0000862, is unsatisfactory in illumination systems, using a LED die? as a radiation source, as these red phosphors only slightly absorb radiation having a wavelength above 300 nm. [0015]Therefore, there is a need to provide an illumination system comprising a novel luminescent material that is excitable by a radiation source with an emission in the blue-violet range and emits in the visible yellow-amber-red range of the electromagnetic spectrum. [0016]Desirable characteristics for illumination systems for general purposes are also a high brightness at economical cost. [0017]Thus the present invention provides an illumination system, comprising a radiation source and a luminescent material comprising a first phosphor capable of absorbing part of the light emitted by the radiation source and emitting light of a wavelength different from that of the absorbed light; wherein said first phosphor comprises europium(III) as an activator in a host lattice selected from the compounds of an anionic oxygen-containing species with a cationic metal species, comprising yttrium(III) and gadolinium(III). [0018]According to a first aspect of the invention, a white-light illumination system comprises a blue light emitting diode having a peak emission wavelength in the range of 325 to 495 nm as a radiation source. [0019]An illumination system comprising this phosphor has an improved quantum yield for the blue to violet excitation radiation having a wavelength .lamda. in the range between 325 and 495 nm. [0020]As the phosphor comprising europium(III) as an activator in a host lattice selected from the compounds of an anionic oxygen-containing species with a cationic metal species, comprising yttrium(III) and gadolinium(III), emits in the red-amber-yellow range of the electromagnetic spectrum, the illumination system comprising such a phosphor is capable of providing red to amber to yellow or white light. [0021]An essential factor is that the europium(III)-activated phosphors are narrow-band emitters in the red-amber-yellow wavelength range emitting between 580 and 700 nm range of the electromagnetic spectrum, so that little or no light is generated at wavelengths that are positioned in the visible spectrum away from the desired red, amber, or yellow wavelengths. [0022]Such a narrow-band emission helps to increase the efficacy of the illumination system. [0023]Applications of the invention include inter alia indicators, traffic lighting, street lighting, security lighting and lighting of automated factory, and signal lighting for cars and traffic as well as general illumination. Applications of the invention include colored also security lighting as well as signage lighting for cars and traffic. Another field of applications includes backlighting of liquid crystal displays. [0024]One embodiment of the invention provides a white light illumination system comprising a blue light emitting diode having a peak emission wavelength in the blue-violet range of 400 to 495 nm as a radiation source and a luminescent material comprising a first phosphor capable of absorbing part of the light emitted by the radiation source and emitting light of a wavelength different from that of the absorbed light; wherein said first phosphor comprises europium(III) as an activator in a host lattice selected from the compounds of an anionic oxygen-containing species with a cationic metal species, comprising yttrium(III) and gadolinium(III), and at least one second phosphor. Continue reading about Illumination system comprising a radiation source and a luminescent material... Full patent description for Illumination system comprising a radiation source and a luminescent material Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Illumination system comprising a radiation source and a luminescent material patent application. Patent Applications in related categories: 20090267486 - Organic light emitting display device - An organic light emitting display device according to one or more embodiments is provided. An organic light emitting display device according to an exemplary embodiment of the present invention includes a reinforcement member disposed on a substrate and having a refractive index of greater than about 2.1, a transflective electrode ... 20090267487 - Organic light emitting display device - An organic light emitting display device includes a substrate; an organic light emitting unit formed on the substrate; and a sealing unit which seals the organic light emitting unit, wherein the sealing unit is formed by alternately stacking at least one first thin film and at least one second thin ... 20090267485 - Phosphor and manufacturing method therefore, and light emission device using the phosphor - To provide a phosphor for manufacturing an one chip type LED illumination, etc, by combining a near ultraviolet/ultraviolet LED and a blue LED, and having an excellent emission efficiency including luminance. The phosphor is given as a general composition formula expressed by MmAaBbOoNn:Z, (where element M is one or more ... 20090267488 - Wavelength converting material and use of same - This invention discloses a wavelength converting material. The wavelength converting material comprises a metal haloaluminate compound phosphor with a chemical formula Mw-pAlyOzXq:Rp, wherein M is at least one element selected from the group of Be, Mg, Ca, Sr, Ba and Zn; X is at least one element selected from the ... ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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