WO2007080541A1 - Light emitting device with a eu-comprising phosphor material - Google Patents

Light emitting device with a eu-comprising phosphor material Download PDF

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Publication number
WO2007080541A1
WO2007080541A1 PCT/IB2007/050068 IB2007050068W WO2007080541A1 WO 2007080541 A1 WO2007080541 A1 WO 2007080541A1 IB 2007050068 W IB2007050068 W IB 2007050068W WO 2007080541 A1 WO2007080541 A1 WO 2007080541A1
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Prior art keywords
systems
phosphor material
emitting device
light emitting
wavelength range
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PCT/IB2007/050068
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French (fr)
Inventor
Thomas JÜSTEL
Petra Huppertz
Detlef Uwe Wiechert
Dominik Uhlich
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Philips Intellectual Property & Standards Gmbh
Koninklijke Philips Electronics N. V.
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Application filed by Philips Intellectual Property & Standards Gmbh, Koninklijke Philips Electronics N. V. filed Critical Philips Intellectual Property & Standards Gmbh
Priority to JP2008549959A priority Critical patent/JP2009524212A/en
Priority to EP07700560A priority patent/EP1979439A1/en
Publication of WO2007080541A1 publication Critical patent/WO2007080541A1/en

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Definitions

  • the present invention is directed to light emitting devices, especially to the field of LEDs and to a light converting Eu-comprising phosphor material.
  • Line emitting phosphors are widely applied as red emitters in fluorescent light emitting devices and emissive displays, e.g. in fluorescent lamps, CRTs, and PDPs.
  • Eu-containing light emitting devices suffer from the drawback that the common Eu-doped materials such as CaS :Eu or Sr 2 SIsNgIEu comprises Eu 2+ ions, which are subject of instability due to its oxidation or reaction with other components present in the light emitting device.
  • Another drawback of Eu 2+ activated red-emitting phosphors according to prior art is their relatively wide emission band, which results in a low lumen equivalent.
  • Eu 3+ activated red-emitting phosphors show a better lifetime stability compared to Eu 2+ , but showing a strong absorption only in the UV-C and VUV spectral range, while the absorption is very weak below the low edge of the charge transfer state around 300nm.
  • phosphor-converted light emitting diodes pcLEDs
  • the LED emits a primary radiation, which is at least partly converted into a secondary radiation with a longer wavelength by the light converting material, the so-called phosphor material.
  • a light emitting device comprising an excitation energy source to deliver a primary energy and a converting element essentially comprising Eu 3+ - phosphor material to at least partly convert the primary energy into a secondary radiation whereby in the excitation spectrum of the Eu-comprising phosphor material at 298 K and 1,013 bar the maximum intensity in the wavelength range between > 460 nm to ⁇ 470 nm is >5% of the maximum intensity in the wavelength range between > 220 nm to ⁇ 320 nm.
  • the term “intensity” denotes the amount of absorbed light (corresponding to an absorption strength).
  • the term “essentially comprising Eu 3+ -phosphor material” means and/or includes especially that >90%, according to another embodiment >95% and according to another embodiment >98% of the Eu comprised in the Eu-comprising material are in the form of Eu 3+ .
  • the spectral (absorption and emission) properties of Eu 3+ materials are more stable over time as compared to Eu 2+ materials, because of the lesser tendency to be oxidized. The lower the remaining Eu 2+ content, the better the lifetime behaviour of the Eu-phosphor material.
  • the excitation energy source can be any suitable energy source to excite the secondary light emission of Eu 3+ -comprising phosphor materials such as electron beam sources (e.g. electron guns in CRTs) or light sources such as organic LEDs, inorganic LEDs or laser diodes. Therefore the primary energy can be the energy of an electron beam or the energy of a radiation.
  • electron beam sources e.g. electron guns in CRTs
  • light sources such as organic LEDs, inorganic LEDs or laser diodes. Therefore the primary energy can be the energy of an electron beam or the energy of a radiation.
  • the terms “wavelength range” or more specific "UV-A spectral range” or “blue spectral range” denote energy ranges not limited only to electro-magnetic radiation energy.
  • a light-emitting device could be operated efficiently with LEDs with blue primary radiation (primary energy).
  • the absorption strength of a converting element depends on the absorption strength of the material itself and on the thickness of the converting element in primary energy, e.g. primary light energy, propagation direction.
  • a more effective light conversion material for instance enables the application of thinner phosphor materials for more compact devices and/or to reduce the risk of re-absorption of the secondary emission and following radiation-less transition leading to an enhanced efficiency of the light emitting device due to a thinner converting element.
  • An enhancement of the blue absorption capability simultaneously also enhances the absorption capability in the near UV-A range between 350nm and 420nm. Therefore, also LEDs emitting within the UV- A spectral range can be used to emit the primary radiation of the pcLED by using a phosphor material according to the present invention.
  • the peak area in the wavelength range between > 680 nm to ⁇ 720 nm is >15% of the peak area in the wavelength range between > 570 nm to ⁇ 720 nm.
  • the LED shows an improved deep red emittance characteristics in that for some applications efficiencies of 100 - 200 Lumen/Watt are feasible. Additionally, the LED shows improved colour point stability due to the stability of the red emitter.
  • peak area denotes the integral amount of light within the specified wavelength range.
  • the atomic dopant level (in atom-% of the trivalent cation of the host lattice) of Eu in the Eu-comprising phosphor material is up to 20%.
  • Higher Eu 3+ concentration would led to pronounced energy transfer of the absorbed energy to the surface and defect sites and thus to quenching of the Eu3+ luminescence, a phenomenon which is known as concentration quenching.
  • the Eu-comprising phosphor material furthermore comprises a co-dopant M selected out of the group comprising Bi, In, Tl, Sb or mixtures thereof.
  • M co-dopant
  • the atomic dopant concentration of M (in atom- %) in the Eu-comprising material is up to 20%. Higher M 3+ concentration would led to pronounced energy transfer of the absorbed energy to the surface and defect sites and thus to quenching of the activator luminescence.
  • the ratio of Eu (in atom-%) towards M (in atom-%) in the Eu comprising material is > 0.1:1 to ⁇ 10:1.
  • the term "the ratio of Eu towards M” means or includes especially that M represents the sum of all co-dopants as described above.
  • the Eu-comprising material is selected out of the group comprising oxides, oxyhalogenides, garnets, vanadates, tungstates, borates, silicates, germanates or mixtures thereof. These materials offer a high electron density at the sites of the oxygen anions within the host lattice leading to improved absorption properties of Eu 3+ .
  • the Eu-comprising material is selected out of the group comprising (Gdi_ x _ z Lu x ) 2 ⁇ 3 :Eu z , (Y 1-x-y- z Gd x Lu y ) 3 Al 5 0i 2 :Eu z , Ba 2 (Yi- ⁇ - y - z Gd x Lu y ) 2 Si 4 ⁇ i 3 :Eu z , (Yi- x - y - z Gd x Lu y )VO 4 :Eu z , (Yi- x - y - z Gd x Lu y )OF:Euz, (Yi -x-y-z Gd x Lu y )OCl:Eu z , Ba(Yi -x-y- z Gd x Lu y )B 9 Oi 6 :Eu z , Ba 3 (Yi-
  • a light-emitting device may be of use in a broad variety of systems and/or applications, amongst them one or more of the following:
  • Fig. 1 shows an excitation spectrum of a Y 2 O 3 IEu material according to prior art
  • Fig. 2 shows an emission spectrum of the material of Fig. 1
  • Fig. 3 shows an excitation spectrum of a Eu-comprising material according to a first Example of a first embodiment of the present invention
  • Fig. 4 shows an emission spectrum of the material of Fig. 3
  • Fig. 5 shows an excitation spectrum of a Eu-comprising material according to a second Example of a second embodiment of the present invention
  • Fig. 6 shows an emission spectrum of the material of Fig. 5
  • Fig. 7 shows an excitation spectrum of a Eu-comprising material according to a third Example of a third embodiment of the present invention
  • Fig. 8 shows an emission spectrum of the material of Fig. 7
  • Fig. 9 shows an excitation spectrum of a Eu-comprising material according to a fourth Example of a fourth embodiment of the present invention
  • Fig. 10 shows an emission spectrum of the material of Fig. 9
  • Fig. 11 shows an emission spectrum of an LED according to a fifth
  • Fig. 12 shows an emission spectrum of an LED according to a sixth
  • Fig. 1 and 2 refer to Y 2 O 3 IEu material with a Eu-doping level of 5% (prior art Eu-component).
  • Fig. 1 shows an excitation spectrum
  • Fig. 2 shows an emission spectrum. It can be clearly seen that the intensity as well as the peak area as described above is much lower than according to materials within the present invention. While the absorption of Eu 3+ phosphors in the UV-C and VUV spectral range is strong, it is only very weak below the low energy edge of the charge transfer state around 300nm.
  • the present invention describes red line emitting Eu 3+ phosphors with relatively strong absorption of UV-A radiation and/or blue radiation due to the enhancement of the weak absorption lines at around 395nm ( 7 Fo - 5 D 3 ) and 465nm ( 7 Fo - 5 D 2 ). This is achieved by using lattices with a high covalency or by co-doping the host lattice by ions having the [Ar]3d 10 , [Kr]4d 10 or [Xe]4f 14 5d 10 electron configuration.
  • the spin forbidden character of the 4f-4f transitions of Eu 3+ is relaxed to a certain extent, which results in an enhanced absorption strength of these transitions.
  • the improved absorption properties enable the efficient application of these materials as a colour converter for organic or inorganic state of the art phosphors converted light emitting diodes with emission wavelength in the UV-A and/or blue spectral range.
  • Suitable Eu-comprising phosphor materials for the absorption enhancement according to the present invention are high covalent lattices such as (Gdi_ x Lu x ) 2 O 3 :Eu, (Yi_ x _ y Gd x Lu y ) 3 Al 5 0i2:Eu, Ba 2 (Y 1-x-y Gd x Lu y ) 2 Si4 ⁇ 13 :Eu, Ba 2 (Y 1-x- y Gd x Lu y ) 2 Ge 4 0i 3 :Eu, (Yi_ x _ y Gd x Lu y )VO 4 :Eu, (Yi_ x _ y Gd x Lu y )OF:Eu, (Yi_ x .
  • high covalent lattices such as (Gdi_ x Lu x ) 2 O 3 :Eu, (Yi_ x _ y Gd x Lu y ) 3 Al 5
  • Eu 3+ is surrounded from ions with high negative charge density. Suitable Eu-doping levels are levels up to atomic 20%. Within these materials, Eu 3+ exhibits a strong covalent interaction with the host lattice influencing the transition probability of the spin forbidden transition in comparison to atomic transition probabilities.
  • the covalent interaction of Eu 3+ with the host lattices can be even more enhanced by co-doping of the host lattice with other triple positive charged ions such as Bi 3+ , In 3+ , Tl 3+ or Sb 3+ or mixtures thereof.
  • suitable In 3+ co-doping levels are up to atomic 10%.
  • the atomic dopant level of M in the Eu-comprising phosphor material is up to 5%.
  • the atomic dopant level of M in the Eu-comprising phosphor material is up to 1%.
  • the ratio in atom% of Eu towards M in the Eu-comprising phosphor material is > 0.5:1 to ⁇ 5:1. According to an embodiment of the present invention, the ratio in atom% of Eu towards M in the Eu-comprising phosphor material is > 1:1 to ⁇ 3:1. In case that more than one co- dopant is present, the term "the ratio of Eu towards M" means or includes especially that M represents the sum of all co-dopants as described above.
  • the absorbed excitation energy will be released by a secondary radiation with longer wavelength.
  • the excited D-levels relax radiation-less to the excited D-ground state 5 Do.
  • transitions to the 7 F 2 state are allowed, while transitions to the 7 F 4 state leading to a deep red emission are spin forbidden.
  • a deep red emission with wavelengths around 700nm are preferred.
  • the high electron density of the Eu 3+ -comprising phosphor materials according to the present invention also influencing the emission properties, where the spin forbidden transition 5 D 0 - » 7 F 4 is enhanced in comparison to the allowed transition 5 Do- » 7 F 2 .
  • Fig. 3 and 4 refer to LaOCl: Eu.
  • Fig.3 shows an excitation spectrum
  • Fig. 4 shows an emission spectrum.
  • the maximum intensity in the wavelength range between > 460 nm to ⁇ 470 nm is approx. 21 % of the maximum intensity in the wavelength range between > 220 nm to ⁇ 320 nm.
  • the peak area in the wavelength range between > 680 nm to ⁇ 720 nm is 22% of the peak area in the wavelength range between > 570 nm to ⁇ 720 nm.
  • Fig. 5 and 6 refer to Sr 3 In 2 Ge 3 Oi 2 IEu.
  • Fig.5 shows an excitation spectrum
  • Fig. 6 shows an emission spectrum.
  • the maximum intensity in the wavelength range between > 460 nm to ⁇ 470 nm is approx. 25 % of the maximum intensity in the wavelength range between > 220 nm to ⁇ 320 nm.
  • the peak area in the wavelength range between > 680 nm to ⁇ 720 nm is 25 %of the peak area in the wavelength range between > 570 nm to ⁇ 720 nm.
  • Fig. 7 and 8 refer to Y 2 SiOs:Eu.
  • Fig.7 shows an excitation spectrum
  • Fig. 8 shows an emission spectrum.
  • the maximum intensity in the wavelength range between > 460 nm to ⁇ 470 nm is approx. 11 % of the maximum intensity in the wavelength range between > 220 nm to ⁇ 320 nm.
  • Fig. 9 and 10 refer to Ca 3 Ga 2 Ge 3 Oi 2 IEu. Fig.9 shows an excitation spectrum
  • Fig. 10 shows an emission spectrum
  • the maximum intensity in the wavelength range between > 460 nm to ⁇ 470 nm is approx. 11 % of the maximum intensity in the wavelength range between > 220 nm to ⁇ 320 nm.
  • the peak area in the wavelength range between > 680 nm to ⁇ 720 nm is 27% of the peak area in the wavelength range between > 570 nm to ⁇ 720 nm.
  • the maximum intensity in the wavelength range between > 460 nm to ⁇ 470 nm is >10% of the maximum intensity in the wavelength range between > 220 nm to ⁇ 320 nm as shown for example for Y 2 SiOsIEu and Ca 3 Ga 2 Ge 3 Oi 2 IEu.
  • the maximum intensity in the wavelength range between > 460 nm to ⁇ 470 nm is >15% of the maximum intensity in the wavelength range between > 220 nm to ⁇ 320 nm.
  • the maximum intensity in the wavelength range between > 460 nm to ⁇ 470 nm is >20% of the maximum intensity in the wavelength range between > 220 nm to ⁇ 320 nm as shown for example for LaOCliEu and Sr 3 In 2 Ge 3 Oi 2 IEu.
  • the peak area in the wavelength range between > 680 nm to ⁇ 720 nm is >20% of the peak area in the wavelength range between > 570 nm to ⁇ 720 nm as shown for example for Ca 3 Ga 2 Ge 3 Oi 2 IEu, Y 2 SiOsIEu, Sr 3 In 2 Ge 3 Oi 2 IEu and LaOCIiEu.
  • Other Eu-comprising phosphor materials can show different peak area ratios.
  • EXAMPLE V Fig. 11 shows an emission spectrum of an LED according to a fifth Example of a fifth embodiment of the present invention. The LED was manufactured as follows:
  • a powder mixture of 20% (Y 5 Gd) 3 Al 5 Oi 2 ICe and 80%Y 2 SiO 5 :Eu were suspended in a fluid silicon precursor compound. A drop of this silicon precursor was placed on a Chip emitting light of the wavelength 465 nm and the silicon polymerized. The LED is then sealed with a plastic lens.
  • Fig. 11 shows a good optical characteristic with a T c value of 3000K.
  • Fig. 12 shows an emission spectrum of an LED according to a sixth
  • Example of a sixth embodiment of the present invention The LED was manufactured as follows:
  • a powder mixture of 20% (Y,Gd) 3 Al 5 Oi 2 :Ce and 80% LaOChEu were suspended in a fluid silicon precursor compound. A drop of this silicon precursor was placed on a Chip emitting light of the wavelength 465 nm and the silicon polymerized. The LED is then sealed with a plastic lens.
  • Eu-doping levels different from 5atom% can be chosen in order to adapt for instance the converting element size or the spectral properties of the converting element to the desired application.
  • the light source of this spectrofluorimeter system is a 150W Xe-lamp in an airflow-cooled housing.
  • the lamp output is focused on the entrance slit of the excitation monochromator (Bentham) with a focal length of 0.5 m.
  • the escaping light from the exit slit of the excitation monochromator is fed into a sample chamber and focused onto the sample material under test via several mirrors. While the sample under test is horizontal orientated the optical axis of the excitation and the emission branch are oriented vertically and nearly parallel. This geometric orientation ensures reliable and quantitative comparative measurements of different samples.
  • the sample chamber is coupled optically to the emission monochromator (Bentham, focal length 0.5m) via a mirror system. Detection of the emitted light occurs with a thermo-electrically cooled photomultiplier tube (PMT) unit mounted to the exit slit of the emission monochromator.
  • PMT thermo-electrically cooled photomultiplier tube
  • the sample under test is shaped as a powder layer of 2 mm thickness and the spot size of the excitation light beam is approx. 2x3 mm 2 .
  • the spectral resolution of the excitation and emission branch was in the order of 1-2 nm.
  • a 1 nm step size was chosen for the determination of the excitation and emission spectra.

Abstract

Light emitting device comprising an excitation energy source to deliver a primary excitation energy and a converting element essentially comprising Eu3+- phosphor material to at least partly convert the primary energy into a secondary radiation whereby in the excitation spectrum of the Eu-comprising phosphor material at 298 K and 1,013 bar the maximum intensity in the wavelength range between ≥ 460 nm to ≤ 470 nm is ≥5% of the maximum intensity in the wavelength range between ≥ 220 nm to ≤ 320 nm. The excitation energy source can be any suitable energy source to excite a secondary light emission such as electron beam sources (e.g. electron guns in CRTs) or light sources such as organic LEDs, inorganic LEDs or laser diodes.

Description

Light emitting device with a Eu-comprising phosphor material
The present invention is directed to light emitting devices, especially to the field of LEDs and to a light converting Eu-comprising phosphor material.
Line emitting phosphors are widely applied as red emitters in fluorescent light emitting devices and emissive displays, e.g. in fluorescent lamps, CRTs, and PDPs.
However, especially Eu-containing light emitting devices suffer from the drawback that the common Eu-doped materials such as CaS :Eu or Sr2SIsNgIEu comprises Eu2+ ions, which are subject of instability due to its oxidation or reaction with other components present in the light emitting device. Another drawback of Eu2+ activated red-emitting phosphors according to prior art is their relatively wide emission band, which results in a low lumen equivalent. Eu3+ activated red-emitting phosphors show a better lifetime stability compared to Eu2+, but showing a strong absorption only in the UV-C and VUV spectral range, while the absorption is very weak below the low edge of the charge transfer state around 300nm. This prevents the application of Eu3+ for instance in phosphor-converted light emitting diodes (pcLEDs), since the emission wavelength of such efficient high brightness LEDs is within the near UV-A spectral range above 350nm or within the blue spectral range. In phosphor converted LEDs, the LED emits a primary radiation, which is at least partly converted into a secondary radiation with a longer wavelength by the light converting material, the so-called phosphor material.
It is an object of the present invention to provide a phosphor converted light-emitting device comprising a stable and efficient Eu-comprising phosphor material.
This object is solved by a light emitting device comprising an excitation energy source to deliver a primary energy and a converting element essentially comprising Eu3+- phosphor material to at least partly convert the primary energy into a secondary radiation whereby in the excitation spectrum of the Eu-comprising phosphor material at 298 K and 1,013 bar the maximum intensity in the wavelength range between > 460 nm to ≤ 470 nm is >5% of the maximum intensity in the wavelength range between > 220 nm to ≤ 320 nm.
In absorption spectra, the term "intensity" denotes the amount of absorbed light (corresponding to an absorption strength). The term "essentially comprising Eu3+-phosphor material" means and/or includes especially that >90%, according to another embodiment >95% and according to another embodiment >98% of the Eu comprised in the Eu-comprising material are in the form of Eu3+. The spectral (absorption and emission) properties of Eu3+ materials are more stable over time as compared to Eu2+ materials, because of the lesser tendency to be oxidized. The lower the remaining Eu2+ content, the better the lifetime behaviour of the Eu-phosphor material.
The excitation energy source can be any suitable energy source to excite the secondary light emission of Eu3+-comprising phosphor materials such as electron beam sources (e.g. electron guns in CRTs) or light sources such as organic LEDs, inorganic LEDs or laser diodes. Therefore the primary energy can be the energy of an electron beam or the energy of a radiation. The terms "wavelength range" or more specific "UV-A spectral range" or "blue spectral range" denote energy ranges not limited only to electro-magnetic radiation energy.
With an enhanced absorption capability of the Eu-comprising phosphor material in the above-specified blue spectral range compared to state in the art materials, a light-emitting device according to the present invention could be operated efficiently with LEDs with blue primary radiation (primary energy). The absorption strength of a converting element depends on the absorption strength of the material itself and on the thickness of the converting element in primary energy, e.g. primary light energy, propagation direction. To obtain an equal absorption strength, a more effective light conversion material (high absorption strength of the material itself) for instance enables the application of thinner phosphor materials for more compact devices and/or to reduce the risk of re-absorption of the secondary emission and following radiation-less transition leading to an enhanced efficiency of the light emitting device due to a thinner converting element. An enhancement of the blue absorption capability simultaneously also enhances the absorption capability in the near UV-A range between 350nm and 420nm. Therefore, also LEDs emitting within the UV- A spectral range can be used to emit the primary radiation of the pcLED by using a phosphor material according to the present invention.
According to an embodiment of the present invention, in the emission spectrum of the Eu-comprising material at 298 K and 1,013 bar the peak area in the wavelength range between > 680 nm to ≤ 720 nm is >15% of the peak area in the wavelength range between > 570 nm to ≤ 720 nm. Here, the LED shows an improved deep red emittance characteristics in that for some applications efficiencies of 100 - 200 Lumen/Watt are feasible. Additionally, the LED shows improved colour point stability due to the stability of the red emitter. The term "peak area" denotes the integral amount of light within the specified wavelength range. According to an embodiment of the present invention, the atomic dopant level (in atom-% of the trivalent cation of the host lattice) of Eu in the Eu-comprising phosphor material is up to 20%. Higher Eu3+ concentration would led to pronounced energy transfer of the absorbed energy to the surface and defect sites and thus to quenching of the Eu3+ luminescence, a phenomenon which is known as concentration quenching.
According to an embodiment of the present invention, the Eu-comprising phosphor material furthermore comprises a co-dopant M selected out of the group comprising Bi, In, Tl, Sb or mixtures thereof. These additional dopants are elements with a large number of electrons on d-orbitals increasing the electron density to enhance the absorption capability of Eu3+ within the host lattice. According to an embodiment of the present invention, the atomic dopant concentration of M (in atom- %) in the Eu-comprising material is up to 20%. Higher M3+ concentration would led to pronounced energy transfer of the absorbed energy to the surface and defect sites and thus to quenching of the activator luminescence. According to an embodiment of the present invention, the ratio of Eu (in atom-%) towards M (in atom-%) in the Eu comprising material is > 0.1:1 to < 10:1. In case that more than one co-dopant is present, the term " the ratio of Eu towards M" means or includes especially that M represents the sum of all co-dopants as described above.
According to an embodiment of the present invention, the Eu-comprising material is selected out of the group comprising oxides, oxyhalogenides, garnets, vanadates, tungstates, borates, silicates, germanates or mixtures thereof. These materials offer a high electron density at the sites of the oxygen anions within the host lattice leading to improved absorption properties of Eu3+.
According to an embodiment of the present invention, the Eu-comprising material is selected out of the group comprising (Gdi_x_zLux)2θ3:Euz, (Y1-x-y- zGdxLuy)3Al50i2:Euz, Ba2(Yi-χ-y-zGdxLuy)2Si4θi3:Euz,
Figure imgf000006_0001
(Yi-x-y-zGdxLuy)VO4:Euz, (Yi-x-y-zGdxLuy)OF:Euz, (Yi-x-y-zGdxLuy)OCl:Euz, Ba(Yi-x-y- zGdxLuy)B9Oi6:Euz, Ba3(Yi-x-y-zGdxLuy)(BO3)3:Euz, (Yi-x-y-zGdxLuy)2Si05:Euz, (Ca1-a Sra)3(Yi-w-x-y-zLuwGaxIny)2Ge30i2:Euz (a, w, x, y = 0.0 - 1.0, z = 0.0 - 0.2), (Ca1- aSra)3(Yi_w_x_y_zLuvGawInx)2Ge30i2:EuyBiz (a, v, w, x = 0.0 - 1.0, y, z = 0.0 - 0.2), LaOM:Eu with M = (Br, Cl, I), Na9[(Yi-x-y-zLuxGdy)Wi0O36]:Euz, (Y1-x-y- zLuxGdy) [P(Mo3Oio)4] :Euz (x, y = 0.0 - 1.0, z = 0.0 - 0.2), or mixtures thereof. Here, Eu3+ is surrounded from ions with high negative charge density leading to an enhanced absorption properties in the near UV-A and blue spectral range.
A light-emitting device according to the present invention may be of use in a broad variety of systems and/or applications, amongst them one or more of the following:
Office lighting systems household application systems shop lighting systems, - home lighting systems, accent lighting systems, spot lighting systems, theatre lighting systems, fibre-optics application systems, - projection systems, self-lit display systems, pixelated display systems, segmented display systems, warning sign systems, medical lighting application systems, indicator sign systems, and - decorative lighting systems portable systems automotive applications green house lighting systems
The aforementioned components, as well as the claimed components and the components to be used in accordance with the invention in the described embodiments, are not subject to any special exceptions with respect to their size, shape, material selection and technical concept such that the selection criteria known in the pertinent field can be applied without limitations.
Additional details, characteristics and advantages of the object of the invention are disclosed in the subclaims, the figures and the following description of the respective figures and examples, which —in an exemplary fashion— show several embodiments of an Eu-comprising phosphor material use in a light emitting device according to the present invention as well as an LED according to embodiments of the present invention.
Fig. 1 shows an excitation spectrum of a Y2O3IEu material according to prior art
Fig. 2 shows an emission spectrum of the material of Fig. 1 Fig. 3 shows an excitation spectrum of a Eu-comprising material according to a first Example of a first embodiment of the present invention Fig. 4 shows an emission spectrum of the material of Fig. 3
Fig. 5 shows an excitation spectrum of a Eu-comprising material according to a second Example of a second embodiment of the present invention Fig. 6 shows an emission spectrum of the material of Fig. 5
Fig. 7 shows an excitation spectrum of a Eu-comprising material according to a third Example of a third embodiment of the present invention Fig. 8 shows an emission spectrum of the material of Fig. 7 Fig. 9 shows an excitation spectrum of a Eu-comprising material according to a fourth Example of a fourth embodiment of the present invention Fig. 10 shows an emission spectrum of the material of Fig. 9 Fig. 11 shows an emission spectrum of an LED according to a fifth
Example of a fifth embodiment of the present invention Fig. 12 shows an emission spectrum of an LED according to a sixth
Example of a sixth embodiment of the present invention.
Fig. 1 and 2 refer to Y2O3IEu material with a Eu-doping level of 5% (prior art Eu-component). Fig. 1 shows an excitation spectrum, Fig. 2 shows an emission spectrum. It can be clearly seen that the intensity as well as the peak area as described above is much lower than according to materials within the present invention. While the absorption of Eu3+ phosphors in the UV-C and VUV spectral range is strong, it is only very weak below the low energy edge of the charge transfer state around 300nm. This prevents the application of Eu3+ in state of the art phosphors for phosphor converted light emitting diodes (pcLEDs), since the minimum emission wavelength for efficient high brightness LEDs is at around 370nm, which is below the strong absorption wavelength range (≤300nm) of the Y2O3 :Eu phosphor material. The absorption lines around 395nm (7Fo - 5D3) and 465nm (7Fo - 5D2) are spin forbidden 4f- 4f transitions and therefore very weak absorption lines.
The present invention describes red line emitting Eu3+ phosphors with relatively strong absorption of UV-A radiation and/or blue radiation due to the enhancement of the weak absorption lines at around 395nm (7Fo - 5D3) and 465nm (7Fo - 5D2). This is achieved by using lattices with a high covalency or by co-doping the host lattice by ions having the [Ar]3d10, [Kr]4d10 or [Xe]4f145d10 electron configuration. By the application of covalent lattices or electron rich co-dopants, the spin forbidden character of the 4f-4f transitions of Eu3+ is relaxed to a certain extent, which results in an enhanced absorption strength of these transitions. The improved absorption properties enable the efficient application of these materials as a colour converter for organic or inorganic state of the art phosphors converted light emitting diodes with emission wavelength in the UV-A and/or blue spectral range.
Suitable Eu-comprising phosphor materials for the absorption enhancement according to the present invention are high covalent lattices such as (Gdi_ xLux)2O3:Eu, (Yi_x_yGdxLuy)3Al50i2:Eu, Ba2(Y1-x-yGdxLuy)2Si4θ13:Eu, Ba2(Y1-x- yGdxLuy)2Ge40i3:Eu, (Yi_x_yGdxLuy)VO4:Eu, (Yi_x_yGdxLuy)OF:Eu, (Yi_x. yGdxLuy)OCl:Eu, Ba:(Yi_x.yGdxLuy)B9Oi6:Eu, Ba3(Yi_x.yGdxLuy)(BO3)3:Eu, (Yi_x_ yGdxLuy)2Siθ5:Eu, (Cai_aSra)3(Yi_w_x_y_zLuwGaxIny)2Ge30i2:Euz (a, w, x, y = 0.0 - 1.0, z = 0.0 - 0.2), (Ca i_a Sra)3(Yi-w-x-y-zLuvGawInx)2Ge30i2:EuyBiz (a, v, w, x = 0.0 - 1.0, y,z = 0.0 - 0.2), LaOM:Eu with M=(Br,Cl,I) or mixtures thereof. Here, Eu3+ is surrounded from ions with high negative charge density. Suitable Eu-doping levels are levels up to atomic 20%. Within these materials, Eu3+ exhibits a strong covalent interaction with the host lattice influencing the transition probability of the spin forbidden transition in comparison to atomic transition probabilities.
The covalent interaction of Eu3+ with the host lattices can be even more enhanced by co-doping of the host lattice with other triple positive charged ions such as Bi3+, In3+, Tl3+ or Sb3+ or mixtures thereof. For example, suitable In3+ co-doping levels are up to atomic 10%. According to another embodiment of the present invention, the atomic dopant level of M in the Eu-comprising phosphor material is up to 5%. According to another embodiment of the present invention, the atomic dopant level of M in the Eu-comprising phosphor material is up to 1%.
According to an embodiment of the present invention, the ratio in atom% of Eu towards M in the Eu-comprising phosphor material is > 0.5:1 to ≤ 5:1. According to an embodiment of the present invention, the ratio in atom% of Eu towards M in the Eu-comprising phosphor material is > 1:1 to < 3:1. In case that more than one co- dopant is present, the term " the ratio of Eu towards M" means or includes especially that M represents the sum of all co-dopants as described above.
The absorbed excitation energy will be released by a secondary radiation with longer wavelength. Before radiation release (electron transition from the excited to the ground state), the excited D-levels relax radiation-less to the excited D-ground state 5Do. According to the transition rules, transitions to the 7F2 state are allowed, while transitions to the 7F4 state leading to a deep red emission are spin forbidden. To increase light efficiency and colour rendering index a deep red emission with wavelengths around 700nm are preferred. The high electron density of the Eu3+-comprising phosphor materials according to the present invention also influencing the emission properties, where the spin forbidden transition 5D0- » 7F4 is enhanced in comparison to the allowed transition 5Do- » 7F2. The following examples show the improved absorption and emission properties of Eu3+ comprising phosphor materials according to the present invention. For a better comparison to prior art, all following samples contain the same Eu-doping level of 5atom% Eu3+. The presence of Eu3+ is predetermined by the material preparation. People skilled in the art know, which starting materials have to be chosen in order to prepare materials essentially comprising Eu3+. EXAMPLE I
Fig. 3 and 4 refer to LaOCl: Eu. Fig.3 shows an excitation spectrum, Fig. 4 shows an emission spectrum.
In fig.3, the maximum intensity in the wavelength range between > 460 nm to ≤ 470 nm is approx. 21 % of the maximum intensity in the wavelength range between > 220 nm to ≤ 320 nm.
In fig.4, the peak area in the wavelength range between > 680 nm to ≤ 720 nm is 22% of the peak area in the wavelength range between > 570 nm to ≤ 720 nm. EXAMPLE II
Fig. 5 and 6 refer to Sr3In2Ge3Oi2IEu. Fig.5 shows an excitation spectrum, Fig. 6 shows an emission spectrum.
In fig.5, the maximum intensity in the wavelength range between > 460 nm to ≤ 470 nm is approx. 25 % of the maximum intensity in the wavelength range between > 220 nm to ≤ 320 nm.
In fig.6, the peak area in the wavelength range between > 680 nm to ≤ 720 nm is 25 %of the peak area in the wavelength range between > 570 nm to ≤ 720 nm. EXAMPLE III
Fig. 7 and 8 refer to Y2SiOs:Eu. Fig.7 shows an excitation spectrum, Fig. 8 shows an emission spectrum.
In fig.7, the maximum intensity in the wavelength range between > 460 nm to ≤ 470 nm is approx. 11 % of the maximum intensity in the wavelength range between > 220 nm to ≤ 320 nm.
In fig.8, the peak area in the wavelength range between > 680 nm to ≤ 720 nm is 21% of the peak area in the wavelength range between > 570 nm to ≤ 720 nm. EXAMPLE IV Fig. 9 and 10 refer to Ca3Ga2Ge3Oi2IEu. Fig.9 shows an excitation spectrum,
Fig. 10 shows an emission spectrum.
In fig.9, the maximum intensity in the wavelength range between > 460 nm to ≤ 470 nm is approx. 11 % of the maximum intensity in the wavelength range between > 220 nm to ≤ 320 nm. In fig.10, the peak area in the wavelength range between > 680 nm to ≤ 720 nm is 27% of the peak area in the wavelength range between > 570 nm to ≤ 720 nm.
According to an embodiment of the present invention, in the excitation spectrum of the Eu-comprising phosphor material at 298 K and 1,013 bar the maximum intensity in the wavelength range between > 460 nm to ≤ 470 nm is >10% of the maximum intensity in the wavelength range between > 220 nm to ≤ 320 nm as shown for example for Y2SiOsIEu and Ca3Ga2Ge3Oi2IEu.
According to another embodiment of the present invention, in the excitation spectrum of the Eu-comprising phosphor material at 298 K and 1,013 bar the maximum intensity in the wavelength range between > 460 nm to ≤ 470 nm is >15% of the maximum intensity in the wavelength range between > 220 nm to ≤ 320 nm.
According to an embodiment of the present invention, in the excitation spectrum of the Eu-comprising phosphor material at 298 K and 1,013 bar the maximum intensity in the wavelength range between > 460 nm to ≤ 470 nm is >20% of the maximum intensity in the wavelength range between > 220 nm to ≤ 320 nm as shown for example for LaOCliEu and Sr3In2Ge3Oi2IEu.
According to an embodiment of the present invention, in the emission spectrum of the Eu-comprising phosphor material at 298 K and 1,013 bar the peak area in the wavelength range between > 680 nm to ≤ 720 nm is >20% of the peak area in the wavelength range between > 570 nm to ≤ 720 nm as shown for example for Ca3Ga2Ge3Oi2IEu, Y2SiOsIEu, Sr3In2Ge3Oi2IEu and LaOCIiEu. Other Eu-comprising phosphor materials can show different peak area ratios. EXAMPLE V Fig. 11 shows an emission spectrum of an LED according to a fifth Example of a fifth embodiment of the present invention. The LED was manufactured as follows:
A powder mixture of 20% (Y5Gd)3Al5Oi2ICe and 80%Y2SiO5:Eu were suspended in a fluid silicon precursor compound. A drop of this silicon precursor was placed on a Chip emitting light of the wavelength 465 nm and the silicon polymerized. The LED is then sealed with a plastic lens.
In Fig. 11 it can be clearly seen that the resulting LED shows a good optical characteristic with a Tc value of 3000K. EXAMPLE VI Fig. 12 shows an emission spectrum of an LED according to a sixth
Example of a sixth embodiment of the present invention. The LED was manufactured as follows:
A powder mixture of 20% (Y,Gd)3Al5Oi2:Ce and 80% LaOChEu were suspended in a fluid silicon precursor compound. A drop of this silicon precursor was placed on a Chip emitting light of the wavelength 465 nm and the silicon polymerized. The LED is then sealed with a plastic lens.
In Fig. 12 it can be clearly seen that the resulting LED shows a good optical characteristic with a Tc value of 3100K.
In other embodiments, Eu-doping levels different from 5atom% can be chosen in order to adapt for instance the converting element size or the spectral properties of the converting element to the desired application.
The particular combinations of elements and features in the above detailed embodiments are exemplary only; the interchanging and substitution of these teachings with other teachings in this and the patents/applications incorporated by reference are also expressly contemplated. As those skilled in the art will recognize, variations, modifications, and other implementations of what is described herein can occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention as claimed. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The invention's scope is defined in the following claims and the equivalents thereto. Furthermore, reference signs used in the description and claims do not limit the scope of the invention as claimed. MATERIALS AND METHODS The spectra of the Eu-comprising materials according to the present invention were measured with an in-house built spectrofluorimeter system:
The light source of this spectrofluorimeter system is a 150W Xe-lamp in an airflow-cooled housing. The lamp output is focused on the entrance slit of the excitation monochromator (Bentham) with a focal length of 0.5 m. The escaping light from the exit slit of the excitation monochromator is fed into a sample chamber and focused onto the sample material under test via several mirrors. While the sample under test is horizontal orientated the optical axis of the excitation and the emission branch are oriented vertically and nearly parallel. This geometric orientation ensures reliable and quantitative comparative measurements of different samples. The sample chamber is coupled optically to the emission monochromator (Bentham, focal length 0.5m) via a mirror system. Detection of the emitted light occurs with a thermo-electrically cooled photomultiplier tube (PMT) unit mounted to the exit slit of the emission monochromator. The system is fully computer controlled by an in-house developed software program based on DOS
The sample under test is shaped as a powder layer of 2 mm thickness and the spot size of the excitation light beam is approx. 2x3 mm2. The spectral resolution of the excitation and emission branch was in the order of 1-2 nm. A 1 nm step size was chosen for the determination of the excitation and emission spectra.

Claims

CLAIMS:
1. Light emitting device comprising an excitation energy source to deliver a primary excitation energy and a converting element essentially comprising Eu3+- phosphor material to at least partly convert the primary energy into a secondary radiation whereby in the excitation spectrum of the Eu-comprising phosphor material at 298K and 1,013 bar the maximum intensity in the wavelength range between > 460 nm to ≤ 470 nm is >5% of the maximum intensity in the wavelength range between > 220 nm to ≤ 320 nm.
2. The light emitting device of claim 1, whereby in the emission spectrum of the Eu-comprising phosphor material at 298 K and 1,013 bar the peak area in the wavelength range between > 680 nm to ≤ 720 nm is >15% of the peak area in the wavelength range between > 570 nm to ≤ 720 nm.
3. The light emitting device of any of the claims 1 to 3 whereby the atomic dopant level of Eu in the Eu-comprising phosphor material is up to 20 %
4. The light-emitting device of any of the claims 1 to 4 whereby the Eu- comprising phosphor material furthermore comprises a co-dopant M selected out of the group comprising Bi, In, Tl, Sb or mixtures thereof.
5. The light emitting device of any of the claims 1 to 5 whereby the atomic dopant concentration of M in the Eu-comprising phosphor material is up to 20 %
6. The light emitting device of any of the claims 1 to 6 whereby the ratio in atom% of Eu towards M in the Eu-comprising phosphor material is > 0.1 : 1 to ≤
10:1.
7. The light emitting device of any of the claims 1 to 7 whereby the Eu- comprising phosphor material is selected out of the group comprising oxides, oxyhalogenides, garnets, vanadates, tungstates, borates, silicates, germanates or mixtures thereof
8. The light emitting device of any of the claims 1 to 8, whereby the Eu- comprising phosphor material is selected out of the group comprising (Gdi_x_ zLux)2O3:Euz, (Yi_x_y_zGdxLuy)3Al50i2:Euz, Ba2(Yi-x-y-zGdxLuy)2Si4θi3:Euz, Ba2(Y1-x- y_zGdxLuy)2Ge40i3:Euz, (Yi_x_y_zGdxLuy)VO4:Euz, (Yi_x_y_zGdxLuy)OF:Euz, (Y1-x-y- zGdxLuy)OCl:Euz, Ba(Yi_x_y_zGdxLuy)B9Oi6:Euz, Ba3(Yi-x-y-zGdxLuy)(BO3)3:Euz, (Yi- x_y_zGdxLuy)2Siθ5:Euz, (Cai_a Sra)3(Yi_w_x_y_zLuwGaxIny)2Ge30i2:Euz (a, w, x, y = 0.0 - 1.0, z = 0.0 - 0.2), (Cai_aSra)3(Yi_w_x_y_zLuvGawInx)2Ge30i2:EuyBiz (a, v, w, x = 0.0 - 1.0, y, z = 0.0 - 0.2), LaOM:Eu with M = (Br, Cl, I), Na9[(Yi-x-y- zLuxGdy)Wi0O36]:Euz, (Yi_x_y_zLuxGdy)[P(Mo3Oio)4]:Euz (x, y = 0.0 - 1.0, z = 0.0 -
0.2) or mixtures thereof
9. A system comprising a light emitting device according to any of the claims 1 to 9 the system being used in one or more of the following applications:
Office lighting systems household application systems shop lighting systems, home lighting systems, - accent lighting systems, spot lighting systems, theatre lighting systems, fibre-optics application systems, projection systems, - self-lit display systems, pixelated display systems, segmented display systems, warning sign systems, medical lighting application systems, indicator sign systems, and decorative lighting systems portable systems automotive applications green house lighting systems
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