Illumination system comprising a radiation source and a fluorescent material

Illumination system including radiation source and fluorescent material

The present invention generally relates to a lighting system including a radiation source and a fluorescent material, wherein the fluorescent material includes a phosphor. The invention also relates to phosphors used in such lighting systems.

More particularly, the present invention relates to an illumination system and fluorescent material that generate special colored light including white light through luminescent down conversion and additive color mixing based on an ultraviolet or blue radiation emitting radiation source. The fluorescent material includes a phosphor. In particular, light-emitting diodes are considered as radiation sources.

Recently, various attempts have been made to manufacture white light-emitting lighting systems by using light-emitting diodes as radiation sources. When red, green, and blue-emitting diode devices are used to generate white light, there is a problem that white light of a desired hue cannot be generated due to changes in the hue, brightness, and other factors of the light emitting diode.

In order to solve these problems, various lighting systems have previously been developed, which utilize fluorescent materials including phosphors to transform the color of light emitted by light emitting diodes to provide visible white light illumination.

Previous lighting systems are particularly based on the three-color (RGB) approach, that is, based on a mixture of three colors, namely red, green and blue. In this case, the latter components can be provided by phosphors or by the primary emission of LEDs, or In the second simplified solution, based on the two-color (BY) approach, yellow light and blue light are mixed. In this case, the yellow component can be provided by the yellow phosphor, and the blue component can be emitted by the original emission of the blue LED. provide.

In particular, the two-color approach, as disclosed in, for example, US Patent 5,998,925, uses InGaN semiconductor blue light emitting diodes combined with Y3Al5O12:Ce(YAG-Ce3+) phosphors. The YAG-Ce3+ phosphor is coated on the InGaN LED, and part of the blue light emitted by the LED is converted into yellow light by the phosphor. Another part of the blue light of the LED passes through the phosphor. Therefore, this system emits both the blue light emitted by the LED and the yellow light emitted by the phosphor. The mixture of blue and yellow emission bands is perceived by the observer as white light, the CRI is in the middle 80s, and the color temperature Tc is in the range from about 6000K to about 8000K.

However, white LEDs based on the two-color approach can only be used in a limited range of general lighting because they lack the red component and cause poor color rendering.

The universal ideal white light lamp features high brightness and high color rendering at economic cost. According to the RGB approach with three emission bands: red at 590-630nm, green at 520-560nm and blue at 450nm, it is possible for the three-color lamp spectrum to increase efficiency and much higher color rendering capabilities. These wavelengths are close to the peaks in the CIE tristimulus function, which is used to define the colors.

Unfortunately, there is no known green light emitter with sufficient efficiency and stability.

Therefore, there is a need to provide new phosphors that can be excited in the near UV to blue light range and emit in the visible green light range. It is also desirable to provide new phosphor mixtures that can emit light in a wide wavelength range from green to red, so that they can be combined with UV/blue LEDs to produce white light with high efficiency and/or high color rendering index ("CRI").

Therefore, the present invention provides a lighting system, including a radiation source and a fluorescent material. The fluorescent material includes at least one phosphor that can absorb part of the light emitted by the radiation source and emit light with a wavelength different from that of the absorbed light; wherein the at least one The phosphor is a garnet with the general formula (Lu1-xya-bYxGdy)3(Al1-zGaz)5O12:CeaPrb, where 0<x<1, 0<y<1, 0<z0.1, 0<a 0.2 and 0<b0.1.

Preferably, the radiation source is selected from radiation sources having emission with a peak emission wavelength in the range of 400-480 nm.

Preferably, the radiation source is a light emitting diode.

Another aspect of the present invention provides a lighting system comprising a fluorescent material, the fluorescent material comprising a garnet having the general formula (Lu1-xya-bYxGdy)3(Al1-zGaz)5O12:CeaPrb and at least one second phosphor, wherein 0 <x<1, 0<y<1, 0<z0.1, 0<a0.2, and 0<b0.1.

In particular, the fluorescent material is a white-emitting phosphor blend, including garnet and red phosphor with the general formula (Lu1-xya-bYxGdy)3(Al1-zGaz)5O12:CeaPrb, where 0<x<1.0 <y<1, 0<z0.1, 0<a0.2, and 0<b0.1.

This red phosphor can be selected from Eu(II)-activated phosphors, selected from (Ca1-xSrx)S:Eu, where 0x1, and (Sr1-x-yBaxCay)2-zSi5-aAlaN8- aOa: Euz, where 0a<5, 0<x1, 0y1, 0<Z1.

The principle of the white-emitting LED according to the present invention is based on RGB mixing, that is, a combination of blue, red and green. The basic element is that the yellow-green and red phosphors are broad-band so that they have a sufficient proportion of emission in the entire spectral range.

The emission spectrum of this fluorescent material has a suitable wavelength to obtain high-quality white light with good color rendering properties at the desired color temperature together with the blue light of the LED and the green light of the garnet according to the present invention.

The white light illuminating device has color coordinates basically on the black body locus of the CIE chromaticity diagram.

By using red and green broad-band emitter phosphors and blue-emitting LEDs that cover the entire spectral range, it is possible to generate white light emission with high color rendering. The mixture using the broadband phosphor according to the present invention can have a higher color rendering index, even as high as 91-93.

Another aspect of the present invention provides a phosphor capable of absorbing part of the light emitted by a radiation source and emitting light having a wavelength different from that of the absorbed light; wherein the phosphor has the general formula (Lu1-xya-bYxGdy) 3 (Al1-zGaz ) 5O12: CeaPrb garnet, where 0<x<1, 0<y<1, 0<z0.1, 0<a0.2 and 0<b0.1.

These cerium-activated lutetium-aluminum-garnet phosphors include primary garnets activated by photoluminescence or X-rays of suitable ions, which include lutetium and cerium. These garnets may also include praseodymium and other cations, including mixtures of cations, as activators.

The main garnet of these materials may be a ternary (two cation) garnet, such as lutetium aluminum garnet (Lu3Al5O12), for example, or may include more than three elements, such as lutetium-yttrium-aluminum garnet ((Lu, Y) 3Al5O12), or lutetium-gallium-aluminum garnet ((Lu3(Al,Ga)5O12), for example.

When used in light sources, especially LEDs, the concentration of lutetium affects the color trajectory of the emitted light. The color trajectory of this phosphor can be additionally fine-tuned using the ratio of two concentrations of Lu:Ce, which simplifies or optimizes the adaptability to any other (yellow or red) phosphors in the LED.

In particular, these garnet compositions in which praseodymium is present in a low concentration as the activator cation are particularly desirable because such compositions also exhibit sharp line emission in the red region of the visible spectrum.

These phosphors are broad-band emitters, in which the visible emission is so wide that there is no 80nm wavelength range in the zone where the visible emission is mainly located.

These garnet phosphors can emit very high-intensity broad bands in the yellow-green spectral range of the visible spectrum under UV and blue excitation, so they can provide green components in LEDs that emit special colors or white light. The total conversion efficiency can reach 90%. Other important features of phosphors include: 1) resistance to quenching of luminescence heat at typical device operating temperatures (eg 80°C); 2) non-interference with the reactivity of the encapsulating resin used in the device; 3) enabling visible light spectrum The internal dead absorption is the smallest suitable absorption distribution; 4) the luminous output is temporarily stable during the operating life of the device; and 5) the composition is controlled to adjust the phosphor excitation and emission performance. These garnet phosphors can be easily synthesized.

Preferably, the fluorescent material of the lighting system includes a phosphor with the general formula (Lu1-xya-bYxGdy)3(Al1-zGaz)5O12:CeaPrb, where 0<x<1, y=0, z=0, a=0.01 And b=0.

In particular, the present invention relates to a specific phosphor composition (Lu0.99Ce0.01) 3Al5O12, which exhibits a high quantum efficiency of 80-90%, a high absorption rate of 60-80% in the range of 370nm-470nm and a From room temperature to 100°C, the luminous lumen output caused by thermal quenching is less than 10% low loss.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a three-color white LED lamp including two phosphor mixtures of the present invention, wherein the phosphor mixture is located in the light path emitted by the LED structure.

Figure 2 shows the coordinates of the phosphor mixture of (Lu0.495Y0.495Ce0.01)3Al5O12 and Sr Ga2S4:Eu in the chromaticity diagram of Commission Internationals de I'Eclairage ("CIE"). Mixtures of these phosphors can be produced with coordinates close to the blackbody locus.

Figure 3 discloses the emission spectrum of a green LED when excited by a blue LED at 460nm.

Figure 4 discloses the emission spectrum of a white LED when excited by a blue LED at 460nm.

Figure 5 discloses the excitation and emission spectra of (Lu0.99Ce0.01)3Al5O12.

Figure 6 discloses the excitation and emission spectra of (Lu0.989Ce0.01Pr0.001)3Al5O12.

Figure 7 discloses the excitation and emission spectra of (Lu0.495Y0.495Ce0.01)3Al5O12.

DETAILED DESCRIPTION OF THE INVENTION The present invention focuses on cerium-activated lutetium-aluminum garnet as a phosphor in any structure of a lighting system containing a radiation source, including but not limited to discharge lamps, fluorescent lamps, LEDs, LDs and X-ray tubes. The term "radiation" as used herein includes radiation in the UV, IR, and visible regions of the electromagnetic spectrum.

Although the phosphor of the present invention is considered to be used in various lighting devices, the present invention is described with specific reference to light-emitting diodes, especially diodes that emit UV and blue light, and find specific applications therein.

The fluorescent material according to the present invention includes cerium-activated lutetium-aluminum garnet as a phosphor.

The phosphor conforms to the general formula (Lu1-xya-bYxGdy)3(Al1-zGaz)5O12:CeaPrb, where 0<x<1, 0<y<1, 0<z0.1, 0<a0.2 and 0<b 0.1.

This type of phosphor material is based on the activated luminescence of cubic garnet crystals. Garnet is a type of material with the crystal chemical formula A3B5O12.

The garnet lattice has three different atomic positions: dodecahedron octahedral coordination, octahedral hexahedral coordination and tetrahedral tetrahedral coordination. Among them, the A cation is octahedral with oxygen and the B cation is octahedral (six) or tetrahedral (Four) Coordination aerobic. The crystal structure is cubic, and each unit cell containing eight chemical formula units has 160 ions. According to the present invention, the A cation is a lutetium ion alone or combined with yttrium and gadolinium, combined and substituted with an activator with cerium and possibly praseodymium. The B cation can be aluminum and possibly gallium or other ions, as well, individually, in combination and/or with substitution. In particular, it has been found that these garnets emit light in response to X-ray stimulation using activator ions substituted in the eight-coordination or six-coordination sites. The particularly important activator ion for X-ray emission in this host material is Ce3+ ion located at the eight coordination site.

Instead of a portion of lutetium in the cerium-activated lutetium-aluminum garnet, the Lu3Al5O12:Ce phosphor with smaller ions such as gadolinium Gd3+ or yttrium Y3+ causes the phosphor emission band to shift from the green to the yellow range.

Instead of cerium-activated lutetium-aluminum garnet with part of the aluminum, the Lu3Al5O12:Ce phosphor with larger ions such as gallium Ga3+ causes the phosphor emission band to shift from the green to the blue range.

Using praseodymium as an auxiliary activator to replace part of the cerium in the cerium-activated lutetium-aluminum garnet has the effect that praseodymium produces a secondary emission concentrated in the red region of the visible spectrum, replacing the typical wide band of cerium-activated lutetium-aluminum phosphors Secondary emission, which is usually located in the center of the yellow region of the visible spectrum. The amount of praseodymium as a secondary activator can vary, depending on the amount of red required in the white output light for a particular application.

Preferably these garnet phosphors may be coated with a thin uniform layer of one or more compounds selected from the fluorides and orthophosphates of elemental aluminum, scandium, yttrium, lanthanum, gadolinium and lutetium, oxides of aluminum, yttrium and lanthanum And aluminum nitride.

The thickness of the layer is usually from 0.001 to 0.02 μm, so it is so thin that it can be penetrated by the radiation from the radiation source without substantial energy loss. These material coatings on the phosphor particles can be applied, for example, by vapor deposition or wet coating processes.

These phosphors respond to parts of the electromagnetic spectrum that have higher energy than the visible part of the spectrum.

In particular, the phosphor according to the present invention responds to ultraviolet light such as in fluorescent lamps and light-emitting diodes, visible light such as in blue-emitting diodes, electrons (as in cathode ray tubes) and X-rays (as in radiography).

The present invention also relates to an illumination system including a radiation source and a fluorescent material, wherein the fluorescent material includes at least one phosphor with the general formula (Lu1-xya-bYxGdy)3(Al1-zGaz)5O12:CeaPrb, wherein 0<x<1 , 0<y<1, 0<z0.1, 0<a0.2, and 0<b0.1.

Radiation sources include semiconductor optical radiation emitters and other devices that emit optical radiation in response to electrical excitation. Semiconductor light radiation emitters include light emitting diode LED chips, light emitting polymers (LEP), organic light emitting devices (OLED), polymer light emitting devices (PLED), and the like.

In addition, with the phosphor composition of the present invention, light-emitting elements such as those present in discharge lamps and fluorescent lamps such as mercury low-pressure and high-pressure discharge lamps, sulfur discharge lamps, and molecular radiator-based discharge lamps are also considered as radiation sources.

In a preferred embodiment of the invention, the radiation source is a light emitting diode.

In the present invention, any configuration of a lighting system including an LED and a cerium-activated lutetium-aluminum garnet phosphor composition is considered, and other well-known phosphors are preferably added. As described above, when irradiated with an LED emitting primary color UV or blue light, They are combined to obtain a special color or white light.

In a preferred embodiment of the present invention, the main radiation source used is the radiation of an LED chip emitting UV or blue light. Particularly good results are obtained with blue LEDs with emission maximums in the range of 400-480nm. Considering the excitation spectrum of the garnet phosphor in particular, it is found that the best value is at 445-460nm.

A variant with particularly good color rendering is the combined use of two phosphors, namely the green-emitting cerium-activated lutetium-aluminum garnet phosphor and the red-emitting europium-excited phosphor in the red phosphor, wherein Cerium-activated lutetium-aluminum garnet phosphor has the general formula (Lu1-xya-bYxGdy)3(Al1-zGaz)5O12:CeaPrb, where 0<x<1, 0<y<1, 0<z0.1, 0 <a0.2 and 0<b0.1, Europium excited phosphor is selected from (Ca1-xSrx)S:Eu where 0x1 and where 0a<5, 0<x1, 0y 1 and 0<z1 (Sr1-x-yBaxCay)2-zSi5-aAlaN8-aOa: Euz.

It is preferable to use europium-excited strontium calcium sulfide, which is a high-chromaticity red phosphor that can be excited from near UV (400 nm) to blue-green light (500 nm) with high quantum efficiency. In order to optimally use this phosphor for the luminescence conversion of primary color LED light, the physical properties of the light must be changed to obtain, for example, the effectiveness, color specifications, and lifespan of the relevant light-emitting device. The chromaticity and quantum efficiency of strontium sulfide excited by europium can be changed by substituting divalent metal ions in the list including Ba, Ca, Mg, and Zn for strontium.

Table 1

The phosphor mixture includes a certain amount and relative proportion of a mixture of cerium-activated garnet structure lutetium-aluminum oxide and divalent europium-activated calcium-strontium sulfide. The apatite structure material has a wide band of visible radiation emission, the yttrium oxide material has a narrow emission in the red-orange region of the visible spectrum, and the relative phosphor ratio makes the composite emission of the first phosphor layer roughly fall on the ICI system xy Inside the warm white ellipse recorded on the chromaticity diagram.

Particularly preferred is a white light-emitting radiation source, which includes an InGaN chip that emits light in the blue range of the visible spectrum and has a peak emission at 455 nm, and a phosphor mixture that includes a corresponding spectral weight ratio of blue: green : Red=1.1:2.4:2.18 and Lu3Al5O12:Ce and CaS:Eu emitting white light, the white light color coordinates x=0.336 and y=0.339, the color rendering index is 83, and the luminous efficiency is about 21 lumens/watt. The spectrum of this white-emitting LED including three different mixtures of Lu3Al5O12: Ce and CaS: Eu is shown in Figure 4.

The detailed structure of this light-emitting device is shown in FIG. 1.

Figure 1 is a schematic diagram of the device of the present invention. The device includes LED1. The LED1 is located in the reflector cup 2. LED1 emits patterned light. Phosphor compositions 4, 5 are located in the pattern. The phosphor composition is embedded in the resin 3. In this example, the reflective cup 2 can change the light pattern if the light is reflected into a space that was not previously covered by the initial light pattern (for example, in a parabolic reflector). It can be appreciated that those skilled in the art can provide any shape of reflector cup 2 that can optimize light emission back to the phosphor composition 4, 5, or optimize the position of the LED 1 to provide a light pattern for effective conversion of any shape. Reflector cup 2. For example, the wall of the reflector cup 2 may be parabolic.

In one embodiment, the device further includes a polymer for sealing the phosphor or phosphor mixture. In this embodiment, the phosphor or phosphor mixture should exhibit high stability performance in the sealant. Preferably, the polymer is optically transparent to prevent significant light scattering. In one embodiment, the polymer is selected from epoxy resins and silicone resins. Various polymers used in the manufacture of LED lamps are known in the LED industry. Adding the phosphor mixture to the liquid that is the polymer precursor can be preformed into an encapsulation. For example, the phosphor mixture may be a powder. The introduction of phosphor particles into the polymer precursor liquid results in the formation of a slurry (ie, a suspension of particles). When polymerized, the phosphor mixture is firmly held in place by the encapsulation. In one embodiment, both the composition and the LED are encapsulated in a polymer.

Phosphors can be applied individually or as a mixture. The phosphor completely or partially absorbs the light from the LED emitting UV/blue light, and forms a full-broadband (especially red with a significant proportion) in other spectral regions (mainly yellow and green) with the desired color point. ) Before launching it.

The color points of black bodies corresponding to different temperatures are given by the black body locus (BBL). Since the color emitted by the black body is considered white, and white light is usually required by the lamp, it is usually hoped that the color point of the light emitted by the luminescent material of the light-emitting lamp should be on or near the BBL. A part of the BBL is shown in FIG. 2. The BBL corresponding to the white light emitting LED has the brightest three color temperature points, and its emission spectrum is shown in FIG. 4.

Another valuable graph is to show the quality of the illumination color of the white-emitting radiation source, which is expressed by the color rendering index (CRI). A CRI of 100 means that the light emitted by the light source is similar to that of a black body source, that is, an incandescent lamp or a halogen lamp. A CRI of 85-95 can be obtained by applying a phosphor screen including Lu3Al5O12:Ce and CaS:Eu in a blue-emitting LED.

Figure 4 shows the color coordinates of a series of lighting systems that provide white light, where white light can be produced by various combinations of blue LEDs and the cerium-activated lutetium-aluminum-garnet phosphor of the present invention and CaS:Eu.

More than one phosphor of the present invention can be combined in the same device to provide color adjustment.

Another group of embodiments relates to a green light-emitting lighting system with particularly good color rendering properties, including a combination of a light-emitting semiconductor element that emits primary color light in the blue spectral range of 420-480 nm and a phosphor mixture, wherein the phosphor mixture comprises The green-emitting cerium-activated lutetium-aluminum garnet phosphor Lu3Al5O12: Ce, the corresponding spectral weight ratio blue: green is selected from 1.0: 2.4 to 1.0: 3.5, can emit color coordinates x = 0.336 and y = 0.339, display Green light with a color index of 83 and a luminous efficiency of about 450 lumens/watt.

Due to the wide absorption band, for the primary color light emitted by the light-emitting semiconductor element, the phosphor exhibits suitable absorption or low reflectivity in the disclosed 370nm-480nm spectral range.

If appropriate, the green-emitting phosphor can be used in combination with another yellow or red-emitting phosphor to produce a special color of light, and is preferably used to produce white light with a high color rendering index >80.

Due to the green-yellow wide-band emission, the green emission shown in FIG. 3 can be produced in some embodiments.

Specific Examples In order to synthesize a phosphor with the general formula (Lu1-xya-bYxGdy)3(Al1-zGaz)5O12:CeaPrb, where 0<x<1, 0<y<1, 0<z0.1, 0<a0.2 and 0<b0.1, one or more raw materials can be oxygen-containing compounds that can be dissolved in nitric acid solution, such as oxides, nitrates, sulfates, acetates, citrates or chloric acid salt. For example, a certain amount of Lu2O3, Al(NO3)39H2O, Ce(NO3)36H2O and AlF3 are mixed and dissolved in a nitric acid solution. The choice of the strength of the acid solution to quickly dissolve the oxygen-containing compound is within the skill of those skilled in the art. Evaporate the nitric acid solution. Ball mill or otherwise thoroughly mix the dried precipitate, and then calcinate in a CO atmosphere at about 1300°C for a sufficient time to ensure sufficient and complete dehydration of the raw material. Calcining can be carried out at a constant temperature. Alternatively, the calcination temperature can be ramped from room temperature to and maintained at the final temperature during the calcination duration. After the intermittent milling step, the calcined material is similarly fired in a reducing atmosphere such as H2, CO, or a mixture of one of these gases and an inert gas at 1500-1700°C for a sufficient time to decompose oxygen-containing compounds, The entire calcined material is converted into the desired phosphor composition.

The resulting powder was milled on a roller table for several hours. The ground powder has an average particle size of 40-60 μm.

Its quantum efficiency is 90%, and its luminous efficiency is between 430 and 4701m/W. The color point is at x=0.33-0.38 and y=0.57-0.58.

Table 2

In Figures 5, 6, and 7 of the accompanying drawings of this specification, the emission spectra of various compounds are shown. When excited with 355nm wavelength radiation, these garnet phosphors were found to give broad-band emission, forming a peak at 515nm.

Figure 5 of the accompanying drawings in this specification shows the excitation and emission spectra of the composition (Lu0.99Ce0.01)3Al5O12.

Figure 6 of the accompanying drawings of this specification shows the excitation and emission spectra of the composition (Lu0.495Y0.495Ce0.01) 3Al5O12.

Figure 7 shows that (Lu0.989Ce0.01Pr0.001)3Al5O12 was found to have a broad band (515-540nm) excitation with a peak extension range of 515-540nm and a side band at 610nm when the excitation was scanned.

It can also be clearly seen from the excitation spectrum that these cerium-activated lutetium-aluminum-garnet phosphors can be effectively excited by radiation with wavelengths of 254 and 355 and 420 nm.

In order to manufacture a white lighting system based on 460nm emitting InGaN LEDs, phosphors including at least one garnet of the general formula (Lu1-xya-bYxGdy)3(Al1-zGaz)5O12: CeaPrb and a red phosphor according to Table 2 The mixture is suspended in the silicone precursor, where 0<x<1, 0<y<1, 0<z0.1, 0<a0.2, and 0<b0.1. A drop of this suspension is deposited on the LED chip and then polymerized. Plastic lens seals the LED.