WO2012042441A1 - Light emitting device comprising a fluidized phosphor - Google Patents

Light emitting device comprising a fluidized phosphor Download PDF

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Publication number
WO2012042441A1
WO2012042441A1 PCT/IB2011/054160 IB2011054160W WO2012042441A1 WO 2012042441 A1 WO2012042441 A1 WO 2012042441A1 IB 2011054160 W IB2011054160 W IB 2011054160W WO 2012042441 A1 WO2012042441 A1 WO 2012042441A1
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WO
WIPO (PCT)
Prior art keywords
light
circulation path
phosphor
emitting device
light emitting
Prior art date
Application number
PCT/IB2011/054160
Other languages
French (fr)
Inventor
Jörg Meyer
René Theodorus WEGH
Boudewijn Lodewijk Kropman
Pieter Joseph Clara Van Der Wel
Josephus Paulus Augustinus Deeben
Jan Cornelis Kriege
Johannes Martinus Jansen
Original Assignee
Koninklijke Philips Electronics N.V.
Philips Intellectual Property & Standards Gmbh
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Publication date
Application filed by Koninklijke Philips Electronics N.V., Philips Intellectual Property & Standards Gmbh filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2012042441A1 publication Critical patent/WO2012042441A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/50—Wavelength conversion elements
    • H01L33/501—Wavelength conversion elements characterised by the materials, e.g. binder
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/64—Heat extraction or cooling elements
    • H01L33/648—Heat extraction or cooling elements the elements comprising fluids, e.g. heat-pipes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/52—Encapsulations
    • H01L33/56—Materials, e.g. epoxy or silicone resin
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/64—Heat extraction or cooling elements
    • H01L33/644—Heat extraction or cooling elements in intimate contact or integrated with parts of the device other than the semiconductor body

Definitions

  • Light emitting device comprising a fluidized phosphor
  • the present invention relates to a light emitting device comprising a fluidized phosphor, a light source, and a circulation path arranged to receive at least a part of the light emitted by said light source.
  • phosphors in lighting devices are to absorb light and reemit light of a different wavelength.
  • phosphors are applied in lighting devices in powder form, or in the form of ceramics like LUMIRAMIC. Phosphors may also be applied in a liquid carrier, which either dissolves or suspends luminescent molecules or particles.
  • a problem associated with phosphors in powder form is heat dissipation occurring from the phosphor layer in lighting devices such as phosphor converted LEDs with remote or vicinity phosphor.
  • lighting devices such as phosphor converted LEDs with remote or vicinity phosphor.
  • heat is generated in the phosphor layer itself, which is related to the Stokes loss.
  • the phosphor layer is heated up through heat flow from the LED. This heat hampers phosphor performance, as luminescent materials usually suffer from thermally induced quenching.
  • Thermal quenching is most prominent in quantum dots and organic phosphors, but is also common in many inorganic phosphor compositions. Any means to remove heat from the phosphor is therefore highly desired, however in classical phosphor layers heat transport is very hard to realize due to the limited heat conductivity of the phosphor itself as well as that of its encapsulants.
  • US 2009/0001372 Al discloses an optoelectronic device comprising a heat source and a heat transfer liquid in order to provide heat removing efficiency. Phosphor particles may be dispersed in the heat transfer liquid.
  • a light emitting device comprising a primary fluidized phosphor, a light source emitting light of a first wavelength, and at least one circulation path arranged to receive at least a part of the light emitted by said light source, wherein at least a part of said primary fluidized phosphor is circulated in said at least one circulation path during operation of said device, thereby converting at least a part of said light of the first wavelength into light of a second wavelength.
  • At least one reservoir containing a secondary fluidized phosphor may be connectably arranged to said at least one circulation path.
  • the secondary fluidized phosphor may be the same as said primary fluidized phosphor circulated in said at least one circulation path. Thereby, fresh phosphor may be introduced in the at least one circulation path by introducing the secondary fluidized phosphor into the at least one circulation path.
  • the secondary fluidized phosphor is different from the primary fluidized phosphor circulated in the at least one circulation path.
  • the emission color of the device can be changed by introducing the secondary fluidized phosphor into the at least one circulation path.
  • a plurality of reservoirs, each containing a unique secondary fluidized phosphor are connectably arranged to said at least one circulation path and/or to each other. Thereby, the emission color of said device can be multiply changed by introducing different secondary fluidized phosphors into the circulation path.
  • each one of the plurality of reservoirs is connectably arranged to a unique circulation path being different from said at least one circulation path.
  • the color emitted from the device may be changed by circulating different secondary fluidized phosphors in said circulation paths, and the secondary phosphors contained in the reservoirs can be separately recollected in separate containers.
  • the reservoirs are suitably arranged aside from said light source, such that the reservoirs do not interfere with light emitted from said light source.
  • the at least one circulation path is suitably a compartment arranged between said light source and an encapsulation layer, which may e.g. be a lens.
  • the compartment surrounds all sides of said light source, such that light can be emitted from all around the light source.
  • the light source may e.g. be a light emitting diode (LED), a lamp or a laser.
  • LED light emitting diode
  • the light source may e.g. be a light emitting diode (LED), a lamp or a laser.
  • the light emitting device suitably further comprises a pump and/or a heat exchanger.
  • the present invention also relates to a method for manufacturing a light emitting device comprising:
  • a secondary fluidized phosphor which may be the same as or different from said primary fluidized phosphor.
  • the method may also comprise the further optional steps of:
  • the invention relates to a method for operating a light emitting device comprising a primary fluidized phosphor, a light source emitting light of a first wavelength and at least one circulation path arranged to receive at least a part of said light of the first wavelength emitted by said light source, said method comprising: circulating said primary fluidized phosphor in said at least one circulation path during operation of said device, thereby converting at least a part of said light of the first wavelength into light of a second wavelength.
  • the method may further comprise the step of introducing into said at least on circulation path a predetermined amount of a secondary fluidized phosphor being the same as said primary fluidized phosphor, whereby said primary fluidized phosphor is refreshed.
  • the method further comprises the step of introducing into said at least one circulation path a predetermined amount of a secondary fluidized phosphor being different from said primary fluidized phosphor, whereby the emission color of said light emitting device is changed.
  • the method further comprises the step of introducing into said at least one circulation path predetermined amounts of a plurality of secondary fluidized phosphors being different from said primary fluidized phosphor, whereby the emission color of said light emitting device may be multiply changed.
  • the invention in another embodiment, relates to a method for operating a light emitting device comprising a plurality of circulation paths, wherein the method comprises the step of arranging the circulation paths such that the color emitted from the device may be changed by circulating different secondary fluidized phosphors in said circulation paths. Thereby, the phosphors may be recollected in separate containers.
  • Fig. 1 is a schematic view of a light emitting device in accordance with a first embodiment of the invention.
  • Fig. 2 is a schematic view of a light emitting device in accordance with a second embodiment of the invention.
  • a fluidized phosphor is highly advantageous in this respect, as it allows for an almost free form of the irradiated and emitting phosphor layer, which in turn guarantees uniform color impression.
  • the light emitting device comprises a fluidized phosphor acting as a color converter and a cooling liquid simultaneously.
  • the cooling is achieved e.g. through the heat capacity and conductivity of the liquid component.
  • a circulating fluidized phosphor system in the light path is suggested.
  • This construction not only imparts excellent cooling properties, but also provides for the possibility for replacing degraded phosphor material during operation of the device, as well as a great flexibility in terms of changing and adapting illumination color.
  • the present invention provides for a possibility to "refresh" the phosphor fluid circulating in the light path, by using a separate phosphor fluid reservoir which may be connected to the path, "circulation path", in which the phosphor fluid circulates.
  • the fluidized phosphor contained in the reservoir may be continuously or temporarily pumped into the circulation path to replace or complement the original phosphor fluid in case it suffers from degradation. This introduction of fresh phosphor fluid may also add to the cooling effect achieved by circulation of the fluid.
  • the reservoir may contain a phosphor fluid which is different from the original circulating phosphor fluid.
  • the color emitted by the device may change during operation of the device by introducing the different phosphor fluids into the circulation path and mixing with the original phosphor fluid.
  • any combination of luminescent dyes i.e. phosphors, dissolved or dispersed in identical or miscible solvents may be used.
  • solutions of Lumogen yellow (F170) (BASF) and Lumogen red (F305) (BASF) in acetone may be used. More specifically, a first solution of Lumogen yellow is circulated along the circulation path to interact with the primary light solely. A first reservoir containing a second solution of Lumogen red is connected to this circulation path and the second solution is slowly introduced into the circulation path. The first solution may be collected in an empty second reservoir and thus be removed from the circulation path, alternatively both solutions share the full volume of the circulation path and the first reservoir.
  • different wavelengths can be achieved depending on the amount of the different phosphors introduced into the circulation path. In this example the secondary wavelength, which is emitted by the luminescent materials, will shift from the yellow to the red spectral region.
  • the color of the device can be changed and adjusted over a wide wavelength range during operation of the device.
  • any combination of luminescent dyes i.e. phosphors, dissolved or dispersed in identical or miscible solvents may be used.
  • three solutions of Lumogens emitting yellow, green and red in acetone may be used. More specifically, a first solution of Lumogen yellow is circulated along the circulation path to interact with the primary light solely. A first reservoir containing a second solution of Lumogen green is connected to this circulation path and the second solution is slowly introduced into the circulation path. The first solution may be collected in an empty reservoir and thus be removed from the circulation path, alternatively both solutions share the full volume of the circulation path and the first reservoir. A second reservoir containing a third solution of Lumogen red is connected to this circulation path and the third solution is slowly introduced into the circulation path.
  • the second solution may be collected in an empty reservoir and thus be removed from the circulation path.
  • two of the solutions, or all three solutions share the full volume of the circulation path and second and/or first reservoir. This example may be extended to an arbitrary amount of different solutions or dispersions containing different luminescent dyes.
  • each reservoir may be connected to a unique circulation path.
  • This embodiment provides for a possibility to circulate different f uidized phosphors in different circulation paths which are separated from each other.
  • the unique circulation paths By combining the unique circulation paths in a suitable way in the light path of the light source, and by continuously or temporary circulating fluidized phosphor in each unique circulation path, the light emitted from the device can be adjusted.
  • This embodiment thus provides for f uidic phosphor screens with adjacent layered or lateral compartments that may be filled individually, allowing for high color variability adjustable to user needs.
  • any combination of luminescent dyes i.e. phosphors, dissolved or dispersed in suitable solvents may be used.
  • two dispersions of inorganic luminescent particles may be used.
  • the first dispersion comprises microcrystalline Y3Al 5 0i 2 :Ce particles in water as dispersant. Na 5 P 3 Oio may be used to avoid sedimentation of the particles.
  • the second dispersion comprises microcrystalline (Ba ⁇ r SisNsiEu particles in water as dispersant. Na 5 P 3 Oio may be used to avoid sedimentation of the particles.
  • As primary light source a blue emitting light emitting diode is used.
  • the color coordinates lie on the Planckian Locus at a correlated color temperature above 5000K.
  • a means is provided to introduce predetermined amounts of the second dispersion into a second circulation path, leading to secondary emission of red light from the (Ba ⁇ r SisNsiEu particles. This light is set to be in such proportions that the correlated color temperature CCT of the light source changes to warm white, i.e. CCT ⁇ 3500K. In this fashion white light sources with adjustable white point may be built.
  • the reservoir(s) are suitably positioned to not interfere with the light path. Further reservoirs, acting as waste containers for degraded phosphor material, may also be included in a device according to the invention.
  • the light source is completely surrounded by the fluidized phosphor.
  • the surrounding liquid acts as a coolant, which in turn renders it possible to replace the light blocking heat sink.
  • light can be emitted from all around the light source, which is of course very advantageous and very much sought after in the art.
  • the light source may be e.g. a light emitting diode (LED), a lamp or a laser.
  • LED light emitting diode
  • the light source may be e.g. a light emitting diode (LED), a lamp or a laser.
  • a “circulation path" in accordance with the present invention is a compartment in which fluidized phosphor can be circulated.
  • the circulation path may e.g. be formed by a space between a frontal lens and a substrate on which a light source is arranged. Any micro fluidic set-up to handle multiple liquids may be used for this purpose.
  • the channels can be arranged to allow for or avoid mixing of the liquids introduced. They can be arranged to allow different fluids to be moved adjacent to each other either side by side or on top of each other or in any combination of the two.
  • the fluidized phosphor(s) are circulated the circulation paths(s) by a pump.
  • a passive thermo-syphon system provides circulation.
  • the fluid may also be moved electrophoretically, through the introduction of suitable charge carriers.
  • a “reservoir” in accordance with the present invention is a compartment in which fluidized phosphors may be stored.
  • the fluidized phosphor stored in a reservoir may be introduced into a circulation path e.g. by using a pump, thermal movement, diffusion or electrophoretical movement.
  • fluidized phosphor relates either to a luminescent material in liquid form or to a non-luminescent and (in the visible and near-UV) non- absorbing liquid, a so-called “optical liquid”, containing a molecular, nano- or
  • microparticulate luminescent material in solid form.
  • the luminescent material may e.g. be dispersed or dissolved in the optical liquid.
  • the optical liquid is chemically inert to the dissolved or dispersed optically active luminescent component(s) and thermally stable. It has preferably a high heat capacity and high thermal conductivity and the viscosity is tuned to the desired application.
  • the refractive index of the liquid can be adapted to that of the dispersed luminescent particles; alternatively in case of a (slight) refractive index mismatch the blue light will be (slightly) scattered, avoiding a very intense LED spot.
  • Solutions, colloids or dispersions of the luminophore in the liquid must be stable at least for the intended device lifetime.
  • the liquids should be non-toxic, non-flammable and have relatively high boiling point and low vapour pressure. Such liquids comprise water, silicones (oils), paraffin and ionic liquids.
  • luminescent materials is not limited other than it has to harmonize with the primary light source (excitability) and should be sufficiently chemically and thermally stable under application conditions. Specific examples include, but are not limited, to the luminescent materials mentioned in the examples above.
  • a light emitting device (1) comprising a primary fiuidized phosphor (2), a light source (3) arranged on a substrate, and a circulation path (4).
  • the primary fiuidized phosphor (2) is circulated (illustrated by arrows in the figure) in the circulation path (4) during operation of said device, thereby converting at least a part of said light of the first wavelength into light of a second wavelength.
  • Two reservoirs (5, 7) containing a secondary fiuidized phosphors (6, 8) are connectably arranged to the circulation path (4).
  • the fiuidized phosphors are circulated by pumps (10).
  • Fig. 2 shows an embodiment of a light emitting device according to the invention, wherein the reservoirs (5, 7) are connectably arranged to unique circulation paths (9, 10) being different from the first circulation path (4).
  • a first reservoir may comprises a first secondary fiuidized phosphor comprising a first optical liquid and a first luminescent material
  • a second reservoir may comprises a second secondary fiuidized phosphor comprising a second optical liquid and a second luminescent material.
  • the first luminescent material may be the same as or different from said second luminescent material.
  • the first optical liquid may be the same as or different from said second optical liquid.
  • a light emitting device may be used in backlights, downlighters, TL- and GLS-retrofit lamps and also in office lighting systems, household application systems, shop lighting systems, home lighting systems, accent lighting systems, spot lighting systems, theater lighting systems, fiber-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, decorative lighting systems portable systems, automotive applications, and green house lighting systems Examples
  • Example 1 Color variable light source with two colors
  • a primary light source is provided, which is preferably a blue emitting LED. This is equipped with a microfluidic device allowing for the introduction of luminescent dyes into the light path.
  • a first solution of Lumogen yellow is circulated along the circulation path to interact with the primary light solely.
  • a first reservoir containing a second solution of Lumogen red is connected to this circulation path and the second solution is slowly introduced into the circulation path.
  • the first solution may be collected in an empty second reservoir and thus be removed from the circulation path, alternatively both solutions share the full volume of circulation path and first reservoir.
  • Example 2 Color variable light source with three or more colors
  • a primary light source is provided, which is preferably a blue emitting LED. This is equipped with a microfluidic device allowing for the introduction of luminescent dyes into the light path.
  • a first solution of Lumogen yellow is circulated along the circulation path to interact with the primary light solely.
  • a first reservoir containing a second solution of Lumogen green is connected to this circulation path and the second solution is slowly introduced into the circulation path.
  • the first solution may be collected in an empty reservoir and thus be removed from the circulation path, alternatively both solutions share the full volume of circulation path and first reservoir.
  • a second reservoir containing a third solution of Lumogen red is connected to this circulation path and the third solution is slowly introduced into the circulation path.
  • the second solution may be collected in an empty reservoir and thus be removed from the circulation path, alternatively two or all three solutions share the full volume of circulation path and second and/or first reservoir.
  • This example may be extended to an arbitrary amount of different solutions or dispersions containing different luminescent dyes.
  • Example 3 White light source with adjustable white point
  • a first dispersion consists of microcrystalline YsAlsO ⁇ Ce particles in water as dispersant Na 5 P 3 Oio may be used to avoid sedimentation of the particles.
  • a second dispersion consists of microcrystalline (Ba ⁇ r SisNsiEu particles in water as dispersant Na 5 P 3 Oio may be used to avoid sedimentation of the particles.
  • As primary light source a blue emitting light emitting diode is used. Through adjustment of the amount of Y 3 AlsOi 2 :Ce particles in the first dispersion interacting with the primary light on their circulation path, secondary yellow light is emitted from the luminescent particles in such a proportion, that a cool white light source obtained.
  • the color coordinates lie on the Planckian Locus at a correlated color temperature above 5000K.
  • a means is provided to introduce predetermined amounts of the second dispersion into the light source, leading to secondary emission of red light from the (Ba ⁇ r SisNsiEu particles. This light is set to be in such proportions that the correlated color temperature CCT of the light source changes to warm white, i.e. CCT ⁇ 3500K. In this fashion white light sources with adjustable white point may be built.

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Manufacturing & Machinery (AREA)
  • Computer Hardware Design (AREA)
  • Power Engineering (AREA)
  • Led Device Packages (AREA)
  • Non-Portable Lighting Devices Or Systems Thereof (AREA)

Abstract

A light emitting device (1) is disclosed, comprising a primary fluidized phosphor (2), a light source (3) emitting light of a first wavelength, and at least one circulation path (4) arranged to receive at least a part of the light emitted by said light source. At least a part of said primary fluidized phosphor is circulated in said at least one circulation path (4) during operation of said device, whereby at least a part of said light of the first wavelength is converted into light of a second wavelength. The invention also relates to a method for manufacturing such a device, as well as to a method for operating such a device.

Description

Light emitting device comprising a fluidized phosphor
FIELD OF THE INVENTION
The present invention relates to a light emitting device comprising a fluidized phosphor, a light source, and a circulation path arranged to receive at least a part of the light emitted by said light source.
BACKGROUND OF THE INVENTION
The function of phosphors in lighting devices is to absorb light and reemit light of a different wavelength. Generally, phosphors are applied in lighting devices in powder form, or in the form of ceramics like LUMIRAMIC. Phosphors may also be applied in a liquid carrier, which either dissolves or suspends luminescent molecules or particles.
A problem associated with phosphors in powder form is heat dissipation occurring from the phosphor layer in lighting devices such as phosphor converted LEDs with remote or vicinity phosphor. In high power LED lighting devices heat is generated in the phosphor layer itself, which is related to the Stokes loss. In addition the phosphor layer is heated up through heat flow from the LED. This heat hampers phosphor performance, as luminescent materials usually suffer from thermally induced quenching.
Thermal quenching is most prominent in quantum dots and organic phosphors, but is also common in many inorganic phosphor compositions. Any means to remove heat from the phosphor is therefore highly desired, however in classical phosphor layers heat transport is very hard to realize due to the limited heat conductivity of the phosphor itself as well as that of its encapsulants.
US 2009/0001372 Al discloses an optoelectronic device comprising a heat source and a heat transfer liquid in order to provide heat removing efficiency. Phosphor particles may be dispersed in the heat transfer liquid.
There is however still a need in the art for avoiding thermal degradation of phosphor particles in lighting devices, and also to improve the possibility to change and adapt the light emitted from the device during operation. SUMMARY OF THE INVENTION
It is an object of the present invention to provide a light emitting device which has improved color over angle performance, integrability of cooling properties and the possibility to adapt illumination colors.
According to a first aspect of the invention, this and other objects are achieved by a light emitting device comprising a primary fluidized phosphor, a light source emitting light of a first wavelength, and at least one circulation path arranged to receive at least a part of the light emitted by said light source, wherein at least a part of said primary fluidized phosphor is circulated in said at least one circulation path during operation of said device, thereby converting at least a part of said light of the first wavelength into light of a second wavelength.
At least one reservoir containing a secondary fluidized phosphor may be connectably arranged to said at least one circulation path. The secondary fluidized phosphor may be the same as said primary fluidized phosphor circulated in said at least one circulation path. Thereby, fresh phosphor may be introduced in the at least one circulation path by introducing the secondary fluidized phosphor into the at least one circulation path.
In another embodiment of the present invention, the secondary fluidized phosphor is different from the primary fluidized phosphor circulated in the at least one circulation path. Thereby, the emission color of the device can be changed by introducing the secondary fluidized phosphor into the at least one circulation path.
In a still further embodiment, a plurality of reservoirs, each containing a unique secondary fluidized phosphor, are connectably arranged to said at least one circulation path and/or to each other. Thereby, the emission color of said device can be multiply changed by introducing different secondary fluidized phosphors into the circulation path.
In another embodiment, each one of the plurality of reservoirs is connectably arranged to a unique circulation path being different from said at least one circulation path. Thereby, the color emitted from the device may be changed by circulating different secondary fluidized phosphors in said circulation paths, and the secondary phosphors contained in the reservoirs can be separately recollected in separate containers.
The reservoirs are suitably arranged aside from said light source, such that the reservoirs do not interfere with light emitted from said light source.
The at least one circulation path is suitably a compartment arranged between said light source and an encapsulation layer, which may e.g. be a lens. In one embodiment, the compartment surrounds all sides of said light source, such that light can be emitted from all around the light source.
The light source may e.g. be a light emitting diode (LED), a lamp or a laser.
The light emitting device according to the invention suitably further comprises a pump and/or a heat exchanger.
The present invention also relates to a method for manufacturing a light emitting device comprising:
providing a light source emitting light of a first wavelength;
providing at least one circulation path arranged to receive at least a part of said light of the first wavelength emitted by said light source;
introducing into said at least one circulation path a primary fluidized phospor for conversion of at least a part of said light of the first wavelength into light of a second wavelength;
providing one reservoir connectably arranged to said at least one circulation path; and
introducing into said reservoir a secondary fluidized phosphor, which may be the same as or different from said primary fluidized phosphor.
The method may also comprise the further optional steps of:
providing a plurality of reservoirs connectably arranged to said at least one circulation path, and/or
connectably arranging a unique circulation path to each one of said plurality of reservoirs.
Furthermore, the invention relates to a method for operating a light emitting device comprising a primary fluidized phosphor, a light source emitting light of a first wavelength and at least one circulation path arranged to receive at least a part of said light of the first wavelength emitted by said light source, said method comprising: circulating said primary fluidized phosphor in said at least one circulation path during operation of said device, thereby converting at least a part of said light of the first wavelength into light of a second wavelength.
The method may further comprise the step of introducing into said at least on circulation path a predetermined amount of a secondary fluidized phosphor being the same as said primary fluidized phosphor, whereby said primary fluidized phosphor is refreshed.
Alternatively, the method further comprises the step of introducing into said at least one circulation path a predetermined amount of a secondary fluidized phosphor being different from said primary fluidized phosphor, whereby the emission color of said light emitting device is changed.
As a further alternative, the method further comprises the step of introducing into said at least one circulation path predetermined amounts of a plurality of secondary fluidized phosphors being different from said primary fluidized phosphor, whereby the emission color of said light emitting device may be multiply changed.
In another embodiment, the invention relates to a method for operating a light emitting device comprising a plurality of circulation paths, wherein the method comprises the step of arranging the circulation paths such that the color emitted from the device may be changed by circulating different secondary fluidized phosphors in said circulation paths. Thereby, the phosphors may be recollected in separate containers.
It is noted that the invention relates to all possible combinations of features recited in the claims. BRIEF DESCRIPTION OF THE DRAWINGS
This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.
Fig. 1 is a schematic view of a light emitting device in accordance with a first embodiment of the invention.
Fig. 2 is a schematic view of a light emitting device in accordance with a second embodiment of the invention.
DETAILED DESCRIPTION
For general illumination, the color of a LED device must not change with the emission angle. A fluidized phosphor is highly advantageous in this respect, as it allows for an almost free form of the irradiated and emitting phosphor layer, which in turn guarantees uniform color impression.
The light emitting device according to the invention comprises a fluidized phosphor acting as a color converter and a cooling liquid simultaneously. The cooling is achieved e.g. through the heat capacity and conductivity of the liquid component.
In accordance with the invention, a circulating fluidized phosphor system in the light path is suggested. This construction not only imparts excellent cooling properties, but also provides for the possibility for replacing degraded phosphor material during operation of the device, as well as a great flexibility in terms of changing and adapting illumination color.
The present invention provides for a possibility to "refresh" the phosphor fluid circulating in the light path, by using a separate phosphor fluid reservoir which may be connected to the path, "circulation path", in which the phosphor fluid circulates. The fluidized phosphor contained in the reservoir may be continuously or temporarily pumped into the circulation path to replace or complement the original phosphor fluid in case it suffers from degradation. This introduction of fresh phosphor fluid may also add to the cooling effect achieved by circulation of the fluid.
The reservoir may contain a phosphor fluid which is different from the original circulating phosphor fluid. Thereby, the color emitted by the device may change during operation of the device by introducing the different phosphor fluids into the circulation path and mixing with the original phosphor fluid.
For this purpose, any combination of luminescent dyes, i.e. phosphors, dissolved or dispersed in identical or miscible solvents may be used. As an example, solutions of Lumogen yellow (F170) (BASF) and Lumogen red (F305) (BASF) in acetone may be used. More specifically, a first solution of Lumogen yellow is circulated along the circulation path to interact with the primary light solely. A first reservoir containing a second solution of Lumogen red is connected to this circulation path and the second solution is slowly introduced into the circulation path. The first solution may be collected in an empty second reservoir and thus be removed from the circulation path, alternatively both solutions share the full volume of the circulation path and the first reservoir. According to this embodiment, different wavelengths can be achieved depending on the amount of the different phosphors introduced into the circulation path. In this example the secondary wavelength, which is emitted by the luminescent materials, will shift from the yellow to the red spectral region.
By using several phosphor reservoirs, each containing a different kind of phosphor fluid, the color of the device can be changed and adjusted over a wide wavelength range during operation of the device.
For this purpose any combination of luminescent dyes, i.e. phosphors, dissolved or dispersed in identical or miscible solvents may be used. As an example, three solutions of Lumogens emitting yellow, green and red in acetone may be used. More specifically, a first solution of Lumogen yellow is circulated along the circulation path to interact with the primary light solely. A first reservoir containing a second solution of Lumogen green is connected to this circulation path and the second solution is slowly introduced into the circulation path. The first solution may be collected in an empty reservoir and thus be removed from the circulation path, alternatively both solutions share the full volume of the circulation path and the first reservoir. A second reservoir containing a third solution of Lumogen red is connected to this circulation path and the third solution is slowly introduced into the circulation path. The second solution may be collected in an empty reservoir and thus be removed from the circulation path. Alternatively, two of the solutions, or all three solutions, share the full volume of the circulation path and second and/or first reservoir. This example may be extended to an arbitrary amount of different solutions or dispersions containing different luminescent dyes.
When using several phosphor reservoirs, each reservoir may be connected to a unique circulation path. This embodiment provides for a possibility to circulate different f uidized phosphors in different circulation paths which are separated from each other. By combining the unique circulation paths in a suitable way in the light path of the light source, and by continuously or temporary circulating fluidized phosphor in each unique circulation path, the light emitted from the device can be adjusted. This embodiment thus provides for f uidic phosphor screens with adjacent layered or lateral compartments that may be filled individually, allowing for high color variability adjustable to user needs.
For this purpose, any combination of luminescent dyes, i.e. phosphors, dissolved or dispersed in suitable solvents may be used. As an example, two dispersions of inorganic luminescent particles may be used. The first dispersion comprises microcrystalline Y3Al50i2:Ce particles in water as dispersant. Na5P3Oio may be used to avoid sedimentation of the particles. The second dispersion comprises microcrystalline (Ba^r SisNsiEu particles in water as dispersant. Na5P3Oio may be used to avoid sedimentation of the particles. As primary light source a blue emitting light emitting diode is used. Through adjustment of the amount of YsAlsO^Ce particles in the first dispersion interacting with the primary light on its circulation path, secondary yellow light is emitted from the luminescent particles in such a proportion, that a cool white light source is obtained. The color coordinates lie on the Planckian Locus at a correlated color temperature above 5000K. A means is provided to introduce predetermined amounts of the second dispersion into a second circulation path, leading to secondary emission of red light from the (Ba^r SisNsiEu particles. This light is set to be in such proportions that the correlated color temperature CCT of the light source changes to warm white, i.e. CCT < 3500K. In this fashion white light sources with adjustable white point may be built. The reservoir(s) are suitably positioned to not interfere with the light path. Further reservoirs, acting as waste containers for degraded phosphor material, may also be included in a device according to the invention.
According to one embodiment of the invention, the light source is completely surrounded by the fluidized phosphor. Thereby, the surrounding liquid acts as a coolant, which in turn renders it possible to replace the light blocking heat sink. As a consequence, light can be emitted from all around the light source, which is of course very advantageous and very much sought after in the art.
In accordance with the present invention, the light source may be e.g. a light emitting diode (LED), a lamp or a laser.
A "circulation path" in accordance with the present invention is a compartment in which fluidized phosphor can be circulated. The circulation path may e.g. be formed by a space between a frontal lens and a substrate on which a light source is arranged. Any micro fluidic set-up to handle multiple liquids may be used for this purpose. The channels can be arranged to allow for or avoid mixing of the liquids introduced. They can be arranged to allow different fluids to be moved adjacent to each other either side by side or on top of each other or in any combination of the two.
Suitably, the fluidized phosphor(s) are circulated the circulation paths(s) by a pump. Alternatively, a passive thermo-syphon system provides circulation. The fluid may also be moved electrophoretically, through the introduction of suitable charge carriers.
A "reservoir" in accordance with the present invention is a compartment in which fluidized phosphors may be stored. The fluidized phosphor stored in a reservoir may be introduced into a circulation path e.g. by using a pump, thermal movement, diffusion or electrophoretical movement.
As used herein, the term "fluidized phosphor" relates either to a luminescent material in liquid form or to a non-luminescent and (in the visible and near-UV) non- absorbing liquid, a so-called "optical liquid", containing a molecular, nano- or
microparticulate luminescent material in solid form. The luminescent material may e.g. be dispersed or dissolved in the optical liquid.
The optical liquid is chemically inert to the dissolved or dispersed optically active luminescent component(s) and thermally stable. It has preferably a high heat capacity and high thermal conductivity and the viscosity is tuned to the desired application. To achieve transparent dispersions of microparticulate matter, the refractive index of the liquid can be adapted to that of the dispersed luminescent particles; alternatively in case of a (slight) refractive index mismatch the blue light will be (slightly) scattered, avoiding a very intense LED spot. Solutions, colloids or dispersions of the luminophore in the liquid must be stable at least for the intended device lifetime. The liquids should be non-toxic, non-flammable and have relatively high boiling point and low vapour pressure. Such liquids comprise water, silicones (oils), paraffin and ionic liquids.
The choice of luminescent materials is not limited other than it has to harmonize with the primary light source (excitability) and should be sufficiently chemically and thermally stable under application conditions. Specific examples include, but are not limited, to the luminescent materials mentioned in the examples above.
With reference to Fig 1, a light emitting device (1) according the present invention is shown, comprising a primary fiuidized phosphor (2), a light source (3) arranged on a substrate, and a circulation path (4). The primary fiuidized phosphor (2) is circulated (illustrated by arrows in the figure) in the circulation path (4) during operation of said device, thereby converting at least a part of said light of the first wavelength into light of a second wavelength. Two reservoirs (5, 7) containing a secondary fiuidized phosphors (6, 8) are connectably arranged to the circulation path (4). The fiuidized phosphors are circulated by pumps (10).
Fig. 2 shows an embodiment of a light emitting device according to the invention, wherein the reservoirs (5, 7) are connectably arranged to unique circulation paths (9, 10) being different from the first circulation path (4).
If several reservoirs are connectably arranged to the circulation path, a first reservoir may comprises a first secondary fiuidized phosphor comprising a first optical liquid and a first luminescent material, and a second reservoir may comprises a second secondary fiuidized phosphor comprising a second optical liquid and a second luminescent material. The first luminescent material may be the same as or different from said second luminescent material. Further, the first optical liquid may be the same as or different from said second optical liquid. Thus, the composition of the fiuidized phosphor circulating in the light path may be altered by using different optical liquids and different luminescent materials. This provides for a great flexibility of the device.
A light emitting device according to the present invention may be used in backlights, downlighters, TL- and GLS-retrofit lamps and also in office lighting systems, household application systems, shop lighting systems, home lighting systems, accent lighting systems, spot lighting systems, theater lighting systems, fiber-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, decorative lighting systems portable systems, automotive applications, and green house lighting systems Examples
Example 1 : Color variable light source with two colors
A primary light source is provided, which is preferably a blue emitting LED. This is equipped with a microfluidic device allowing for the introduction of luminescent dyes into the light path. A first solution of Lumogen yellow is circulated along the circulation path to interact with the primary light solely. A first reservoir containing a second solution of Lumogen red is connected to this circulation path and the second solution is slowly introduced into the circulation path. The first solution may be collected in an empty second reservoir and thus be removed from the circulation path, alternatively both solutions share the full volume of circulation path and first reservoir.
Example 2: Color variable light source with three or more colors
A primary light source is provided, which is preferably a blue emitting LED. This is equipped with a microfluidic device allowing for the introduction of luminescent dyes into the light path. A first solution of Lumogen yellow is circulated along the circulation path to interact with the primary light solely. A first reservoir containing a second solution of Lumogen green is connected to this circulation path and the second solution is slowly introduced into the circulation path. The first solution may be collected in an empty reservoir and thus be removed from the circulation path, alternatively both solutions share the full volume of circulation path and first reservoir. A second reservoir containing a third solution of Lumogen red is connected to this circulation path and the third solution is slowly introduced into the circulation path. The second solution may be collected in an empty reservoir and thus be removed from the circulation path, alternatively two or all three solutions share the full volume of circulation path and second and/or first reservoir. This example may be extended to an arbitrary amount of different solutions or dispersions containing different luminescent dyes.
Example 3 : White light source with adjustable white point
A first dispersion consists of microcrystalline YsAlsO^Ce particles in water as dispersant Na5P3Oio may be used to avoid sedimentation of the particles. A second dispersion consists of microcrystalline (Ba^r SisNsiEu particles in water as dispersant Na5P3Oio may be used to avoid sedimentation of the particles. As primary light source a blue emitting light emitting diode is used. Through adjustment of the amount of Y3AlsOi2:Ce particles in the first dispersion interacting with the primary light on their circulation path, secondary yellow light is emitted from the luminescent particles in such a proportion, that a cool white light source obtained. The color coordinates lie on the Planckian Locus at a correlated color temperature above 5000K. A means is provided to introduce predetermined amounts of the second dispersion into the light source, leading to secondary emission of red light from the (Ba^r SisNsiEu particles. This light is set to be in such proportions that the correlated color temperature CCT of the light source changes to warm white, i.e. CCT < 3500K. In this fashion white light sources with adjustable white point may be built.
The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

Claims

CLAIMS:
1. A light emitting device (1) comprising:
a primary fluidized phosphor (2),
a light source (3) emitting light of a first wavelength, and
at least one circulation path (4) arranged to receive at least a part of the light emitted by said light source,
wherein at least a part of said primary fluidized phosphor (2) is circulated in said at least one circulation path (4) during operation of said device, thereby converting at least a part of said light of the first wavelength into light of a second wavelength.
2. A light emitting device according to claim 1, wherein at least one reservoir (5) containing a secondary fluidized phosphor (6) is connectably arranged to said at least one circulation path (4).
3. A light emitting device according to claim 2, wherein said secondary fluidized phosphor (6) is the same as said primary fluidized phosphor (2) circulated in said at least one circulation path.
4. A light emitting device according to claim 2, wherein said secondary fluidized phosphor (6) is different from said primary fluidized phosphor (2) circulated in said at least one circulation path.
5. A light emitting device according to any one of the preceding claims, wherein a plurality of reservoirs (5, 7), each containing a unique secondary fluidized phosphor (6, 8), are connectably arranged to said at least one circulation path (4), and/or to each other.
6. A light emitting device according to claim 5, wherein each one of said plurality of reservoirs (5, 7) is connectably arranged to a unique circulation path (9, 10) being different from said at least one circulation path (4).
7. A light emitting device according to any one of the claims 2-6, wherein said reservoirs (5, 7) are arranged aside from said light source (3), such that the reservoirs (5, 7) do not receive any light emitted from said light source.
8. A light emitting device according to any one of the preceding claims, wherein said at least one circulation path (4) is a compartment arranged between said light source (3) and an encapsulation layer.
9. A light emitting device according to claim 8, wherein said compartment surrounds all sides of said light source.
10. A light emitting device according to any one of the preceding claims, further comprising at least one pump (10).
11. A light emitting device according to any one of the preceding claims, further comprising a heat exchanger.
12. A method for manufacturing a light emitting device (1) comprising:
providing a light source (3) emitting light of a first wavelength; - providing at least one circulation path (4) arranged to receive at least a part of said light of the first wavelength emitted by said light source (3);
introducing into said at least one circulation (4) path a primary fluidized phospor (2) for conversion of at least a part of said light of the first wavelength into light of a second wavelength;
- providing a reservoir (5) connectably arranged to said at least one circulation path; and
introducing into said reservoir (5) a secondary fluidized phosphor (6), which may be the same as or different from said primary fluidized phosphor.
13. A method according to claim 12, further comprising:
providing a plurality of reservoirs connectably arranged to said at least one circulation path.
14. A method according to claim 13, further comprising:
connectably arranging a unique circulation path (9, 10) to each one of said plurality of reservoirs (5, 7).
15. A method for operating a light emitting device (1) comprising a primary fluidized phosphor (2), a light source (3) emitting light of a first wavelength and at least one circulation path (4) arranged to receive at least a part of said light of the first wavelength emitted by said light source (3), said method comprising:
circulating said primary fluidized phosphor (2) in said at least one circulation path (4) during operation of said device, thereby converting at least a part of said light of the first wavelength into light of a second wavelength.
16. A method according to claim 15, further comprising:
introducing into said at least one circulation path (4) a predetermined amount of a secondary fluidized phosphor (6) being the same as said primary fluidized phosphor, thereby refreshing said primary fluidized phosphor.
17. A method according to claim 15, further comprising:
introducing into said at least one circulation path (4) a predetermined amount of a secondary fluidized phosphor (6) being different from said primary fluidized phosphor, thereby changing the emission color of said light emitting device.
18. A method according to claim 15, further comprising:
introducing into said at least one circulation path (4) predetermined amounts of a plurality of secondary fluidized phosphors (6, 8) being different from said primary fluidized phosphor,
thereby multiply changing the emission color of said light emitting device.
19. A method according to claim 15, wherein a plurality of circulation paths (9,
10) are arranged to receive at least a part of said light of the first wavelength, said method further comprising:
arranging said circulation paths (9, 10) such that the color emitted from the device may be changed by circulating different secondary fluidized phosphors in said circulation paths,
thereby providing for recollection of the secondary phosphors in separate containers.
PCT/IB2011/054160 2010-09-28 2011-09-22 Light emitting device comprising a fluidized phosphor WO2012042441A1 (en)

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