DE102013223902A1 - Thermoformed phosphor wheel and lighting device with this phosphor wheel and excitation radiation source - Google Patents

Abstract

The invention proposes a lighting device with a deep-drawn phosphor wheel (12) for converting excitation radiation into conversion light. In this case, an annular or annular segment-shaped recess (140) for the phosphor (180) is introduced by deep drawing into an initially planar carrier substrate (120). As a result, it is advantageously possible to use commercially available metal carrier substrates with a highly reflective surface, which only have to be reshaped. The embedding of the phosphor in the deep-drawn depression (140) results in improved heat dissipation from the embedded phosphor (180) into the carrier substrate (120). In addition, the embedding of the phosphor (180) in the preferably mirrored, deep-drawn depression (140) also causes an increase in the conversion efficiency.

Description

Technical area

The present invention relates to a phosphor wheel for converting excitation radiation into conversion light and to a method for producing such a phosphor wheel. In addition, the invention also relates to a lighting device, ie an arrangement of phosphor wheel and excitation radiation source, optionally supplemented by further optical components.

Such a phosphor wheel lighting device is particularly applicable as a light generating unit in a projector, e.g. for video projectors or data projectors, but also for headlight applications in the automotive sector as well as for lighting equipment in the entertainment, architectural and general lighting sector.

State of the art

From the prior art, for example the document US 2010/0245777 A1 , Lighting devices for projection applications are known, which have a phosphor wheel with one or more phosphors. In this case, these illumination devices comprise an excitation radiation source which excites the phosphor to emit light at a wavelength which is different from the excitation radiation wavelength (wavelength conversion of the excitation radiation by means of a phosphor). Usually, the phosphors in the form of circular or annular tracks or segments are arranged successively in the direction of rotation on a disk-shaped carrier substrate of the phosphor wheel, so that the light emitted by the respective phosphor light (conversion light) is generated sequentially in time and fed to the imaging system.

The excitation radiation source used is preferably lasers, for example laser diodes. In this case, the technology is also known as LARP ("Laser Activated Remote Phosphor").

The coating of a phosphor wheel 100 ( 2a , b) with phosphor is carried out according to previous practice so that raised phosphor lanes or segments 110 of defined layer thickness and width on a disk-shaped carrier substrate 120 is applied. The sublime fluorescent web 110 is particularly clearly visible in the enlarged schematic cross-sectional view 2b. In practice, the layer thickness is typically between about one hundred and a few hundred micrometers, depending on the type of phosphor. The carrier substrate 120 consists of a good heat-conducting metal, such as aluminum, the surface of which is tempered with a highly reflective layer.

A structured carrier substrate surface would have the advantage of a more efficient heat dissipation from the phosphor into the carrier substrate due to the increased surface area. Highly reflective coatings on structured surfaces are difficult to produce.

The document US 2010/0328617 A1 discloses a phosphor wheel with three annular phosphor segments for a red, green or blue phosphor (R, G, B). For this purpose, provided for the irradiation with excitation radiation front side of a disc-shaped carrier substrate is provided with an annular groove in which the phosphors are embedded. At the bottom of the annular groove, reflecting structures are provided to increase the coupling-out efficiency for the conversion light.

Presentation of the invention

The object of the present invention is to provide an improved phosphor wheel.

This object is achieved by a phosphor wheel for a lighting device for converting excitation radiation into conversion light, which is designed for rotation about an axis of rotation, with a disk-shaped carrier substrate having a front and a rear side and at least one arranged on a front side of the carrier substrate and with excitation radiation irradiated phosphor region, wherein the phosphor region is formed by a recess in the front side of the carrier substrate and wherein in the recess at least one phosphor layer is embedded, characterized in that the recess is formed by deep drawing.

Particularly advantageous embodiments can be found in the dependent claims.

The method-related object of the invention is achieved by the independent method claim. Further advantageous method steps and embodiments can be found in the dependent claims.

In addition, protection is claimed on a lighting device with the phosphor wheel according to the invention.

In the following, features that relate more to the subject aspects of the invention will also be described, along with features that characterize the procedural aspects together to facilitate the understanding of the technical context of the invention.

The basic idea of the present invention is to provide, on the front side of an at least substantially planar carrier substrate, at least one, preferably annular or circular segment, recess by deep drawing and to use this deep-drawn depression for the at least one phosphor region. embed at least one phosphor in at least part of the deep-drawn well. As a result, the phosphor web is no longer raised on a completely planar carrier substrate but embedded in the depression. The depth and width of the recess is adjusted to the desired layer thickness and width of the phosphor web.

Preferably, as a carrier substrate for the deep drawing of the at least one recess, a plane reflecting disk, in particular metal disk, is provided. As a result, it is advantageously possible to use commercially available metal carrier substrates with a highly reflective surface, which only have to be reshaped. In principle, however, any material is suitable for the carrier substrate which is sufficiently ductile for thermoforming and preferably can be mirrored well. Due to the deep-drawing process, a depression on one side inevitably results in an increase on the other side.

The deep-drawn depression achieves an enlargement of the surface of the carrier substrate and thus improved heat dissipation from the embedded phosphor into the carrier substrate. In addition, the embedding of the phosphor in the preferably mirrored depression also causes an increased lateral backscatter of the converted light and the unconverted portion of the excitation radiation and consequently a more efficient use of the conversion light or improvement of the conversion efficiency. Finally, the dimensional stability (stiffening) of the carrier substrate structured in this way as a result of the deepening or deep-drawing causes a smaller axial movement of the phosphor wheel at its peripheral edge (reduced fluttering at the edge by reducing the curvature or deflection of the carrier substrate) where the phosphor is embedded , Also, by reducing the axial movement at the edge, a smoother running of a wheel rotating rapidly in a projector is effected. The phosphor web therefore moves with greater precision through the narrow gap between the excitation radiation and conversion optics. In order to further increase the dimensional stability of the carrier substrate, further stiffening structures may be provided.

The cross-section of the recess and thus the thermoforming cross-section are preferably formed as at least approximately trapezoid with transition radii. This has the decisive advantage that the usually brittle surface coating in the region of the plane, deep-drawn plane of the annular circumferential trapezium, so to speak on the planned "bottom" of the depression does not rupture. For this purpose, the thermoforming tool is suitably shaped such that this critical surface is clamped during deep drawing between two plane-parallel surfaces of the tool. As a result, this area, which ultimately forms the flat bottom of the depression, is not subject to bending, shearing, stretching or compression during deep drawing. It retains its original structure without damaging the surface finish layer. The flat floor remains free of cracks, warping, roughening, so that the high reflectivity of the coated surface is not reduced. This is important for reasons of efficiency, because the excitation radiation entering the embedded phosphor on the front side of the phosphor wheel and the partly converted light should be reflected back as far as possible without optical losses. The enclosing flanks of the depression also reflect, despite possible small surface cracks, part of the light scattered to the side back into the conversion layer, so that less light is lost in comparison to the conventional raised layer. In addition, prevent the flanks of the recess that the phosphor web flows uncontrollably in the width during the manufacturing process. Rather, due to the embedding between the flanks and the two-sided edge of the phosphor web is defined sharper.

In addition, however, the cross section of the recess can also be chosen differently, for example as a trough-shaped circular section.

As the next step for producing the phosphor wheel according to the invention, a usually initially homogeneous viscous mixture of a phosphor, for example CaAlSiN ₃ : Eu as red phosphor, and a carrier matrix, for example optical silicones, sodium silicates, etc., is prepared and introduced into the recess of the carrier substrate. In addition, it is advantageous to subsequently densify the phosphor on the carrier substrate. This can be achieved with vibration or even more intensively by centrifugal force, in which the carrier substrate is held in a corresponding holder in a centrifuge so that a centrifugal force in the direction perpendicular to the carrier substrate surface is effective (centrifugal compression). Because the side flanks of the depression prevent lateral flow of the viscous mixture, the centrifugal force causes a vertical separation between the phosphor grains and the floating, excess, poorly heat-conductive matrix material. In other words, this phosphor compaction towards the bottom leads to an increase in the phosphor concentration on the carrier substrate surface. The phosphor is thus concentrated directly and with a minimal amount of matrix material on the surface of the depression on the carrier substrate, which enables optimum thermal bonding and dissipation of the heat loss in the carrier substrate resulting from the conversion. In addition, the thermal conductivity of the densest packed near-surface phosphor layer reaches a maximum value, so that the heat conduction within the phosphor / matrix mixture is maximized. Another advantage is that due to the maximum densification, a thinner phosphor layer is sufficient with the same conversion efficiency. In turn, a thinner phosphor layer favors efficient heat removal. After separation and densification, the phosphor layer, depending on the type of matrix material, dried, cured, baked, etc. and is then ready for use.

The densification can also be assisted by the use of phosphor particles with different particle sizes (volume fractions). Thus, the space between the densest packed large phosphor particles can be filled with the next closest packed, and this in turn by the next smaller, etc .. However, the conversion efficiency of the phosphor decreases with the proportion of diminishing phosphor particles again.

• A) Bereitstellen eines planen Trägersubstrats,
• B) Formen mindestens einer Vertiefung in das Trägersubstrat durch Tiefziehen,
• C) Einbetten mindestens einer Leuchtstoffschicht in die mindestens eine Vertiefung.

The method according to the invention for producing a phosphor wheel having the features according to the invention comprises in particular the following method steps:

• A) providing a planar carrier substrate,
• B) forming at least one recess in the carrier substrate by deep drawing,
• C) embedding at least one phosphor layer in the at least one recess.

Preferably, the carrier substrate provided in process step A) is already mirrored or is mirrored in an additional process step. The recess is preferably formed annular or circular segment. In this case, two or more phosphor layers of different phosphors can also be sequentially embedded in the depression. By different phosphors are meant in particular phosphors which emit differently colored conversion light. This can be used to generate a sequential sequential sequence of different light colors.

Preferably, during the process step B), the region of the carrier substrate provided for the flat bottom of the depression is clamped between two plane-parallel surfaces of the deep drawing tool. In this way, this area largely retains its original structure. In particular, any surface coating layer possibly present on the carrier substrate is thus not damaged.

• C1) Bereitstellen einer Mischung aus Leuchtstoff und Trägermatrix,
• C2) Einfüllen der Mischung in die Vertiefung,
• C3) Verdichtung des Leuchtstoffs in Richtung des Bodens der Vertiefung, beispielsweise durch Vibrieren oder Fliehkraftverdichten, oder beides,
• C4) Trocknen der Leuchtstoffschicht in der Vertiefung.

In addition, process step C) may comprise the following substeps:

• C1) providing a mixture of phosphor and carrier matrix,
• C2) filling the mixture into the depression,
• C3) densification of the phosphor in the direction of the bottom of the depression, for example by vibration or centrifugal compression, or both,
• C4) drying the phosphor layer in the recess.

Sub-step C3 therefore sets a gradient of the phosphor density which increases from the surface of the phosphor web to the bottom of the depression.

Brief description of the drawings

In the following, the invention will be explained in more detail with reference to exemplary embodiments. The figures show schematically:

1a , b an embodiment of a phosphor wheel according to the invention,

2a , b a phosphor wheel according to the prior art,

3a C different phases of the production of the phosphor web,

4 a flowchart for the production of a phosphor wheel according to 1a , b,

5 a lighting device with a phosphor according to 1a , b.

Preferred embodiment of the invention

Identical or similar features may be referred to below for the sake of simplicity with the same reference numerals.

1a shows a schematic representation of an embodiment of a phosphor according to the invention 12 in a schematic plan view of the for the irradiation with excitation radiation provided front side 130 of the phosphor wheel 12 , For this purpose, first a circular disk-shaped carrier substrate 120 provided from a mirrored aluminum disc with a thickness of about 0.5 mm (step A in 4 ). Into the intended for the irradiation with excitation radiation front 130 of the phosphor wheel 12 is by deep drawing a circular ring or annular segment-shaped depression 140 trained in 1b is shown in an enlarged cross-sectional view (step B in FIG 4 ). The depression 140 has a trapezoidal cross-section with a depth slightly greater than the thickness of the phosphor layer to be applied of 100 to 300 microns. For this purpose, the thermoforming tool is equipped with a suitably shaped stamp. On the back side 150 of the phosphor wheel 12 is by deep-drawing process one to the depression 140 equal increase 160 educated.

The above definition of the front and back of the phosphor wheel is used for conceptual simplification and appears otherwise appropriate. However, it is of course not restrictive to interpret.

After deep drawing B becomes the depression 140 filled with a viscous mixture of a carrier matrix M1 (for example sodium silicate) and a phosphor M2 (for example YAG: Ce (Y _0.96 Ce _0.04 ) ₃ Al _3.75 Ga _1.25 O ₁₂ as green phosphor) (method step C2 in FIG 4 ). As in 3a with reference to a schematic cross-sectional view of the phosphor web 180 2, the two mixture components M1, M2 are mixed at least approximately homogeneously and the mixture is provided for the subsequent method step C2 (method step C1 in FIG 4 ). To the phosphor M2 in the direction of the ground 170 the depression 140 to compact the carrier substrate 120 with the viscous mixture M1, M2 subjected to vibration or centrifugal compression (method step C3 in FIG 4 ). With increasing centrifugal force, the mixture segregates and the phosphor M2 condenses near the bottom. In 3b is the concentration of the carrier matrix M1 in the ground-near region of the still viscous phosphor web 180 already lower (M1 <M2) than in the near-surface region (M1> M2). In 3c the phosphor M2 near the ground has almost completely condensed (M1 << M2) and near the surface remains the excess carrier matrix M1 (M1 >> M2). Thereafter, the still viscous phosphor web is dried (step C4 in 4b ) and is then ready for use. Preferably, the phosphor layer 180 just with the immediately surrounding surface of the carrier substrate 120 educated.

In addition, further phosphors can be embedded in corresponding segments of the depression in order to convert the excitation radiation into temporally sequentially differently colored conversion light if required.

5 shows a schematic representation of a lighting device 1 with a phosphor wheel according to the invention 12 , The deep-drawn depression with the embedded phosphor web and the rear elevation are not recognizable in this schematic representation, but correspond in this embodiment, in 1a b illustrated embodiment of the phosphor web.

The lighting device 1 comprises an excitation radiation source designed as a laser diode array 2 which has a plurality of laser diodes 3 includes. Their respective laser wavelength can in principle be designed the same or different as needed. Other radiation sources are also conceivable, such as those comprising LASER, superluminescent diodes, LEDs, organic LEDs and the like. The excitation radiation source 2 is designed to excite radiation 4 in the blue or ultraviolet spectral range, preferably in the range 440-470 nm, particularly preferably at about 450 nm, since this represents a suitable excitation wavelength for most phosphors and can also be used as a blue color channel. About optical elements 5 - 11 becomes the light of these laser diodes 3 on the phosphor wheel 12 directed. The two optical elements 7 and 8th form a miniature telescope. In addition, in the beam path of the optical elements 5 - 11 a diffuser 30 arranged to by scattering the excitation radiation 4 an expanded intensity profile on the phosphors of the phosphor wheel 12 to create. The from the phosphor wheel 12 converted and emitted light is from two lenses 11 . 10 collected and collimated and then passes through a dichroic mirror 9 which is designed to reflect light in the blue spectral range and to transmit light in the non-blue spectral range, ie light with longer wavelengths and consequently also the conversion light. By this interpretation, the dichroic mirror serves to merge the phosphor wheel 12 converted and emitted light with the through a segment-shaped through hole of the phosphor wheel 12 (in 1a not shown) transmitted excitation radiation 4 , For deflecting the transmitted excitation radiation 4 are three deflecting mirrors 13 provided in the beam path in each case at an angle of 45 ° to the incident excitation radiation 4 are arranged ("wrap-around" path of the excitation radiation). There is another diffuser in this wrap-around path 31 arranged. The means of the dichroic mirror 9 merged light or excitation radiation passes through a focusing lens 15 in an optical integrator 17 ,

The invention proposes a lighting device with a deep-drawn phosphor wheel for converting excitation radiation into conversion light. This is in a first plan Carrier substrate introduced an annular or annular segment-shaped recess for the phosphor by deep drawing. As a result, it is advantageously possible to use commercially available metal carrier substrates with a highly reflective surface, which only have to be reshaped. By embedding the phosphor in the deep-drawn depression improved heat dissipation from the embedded phosphor is achieved in the carrier substrate. In addition, the embedding of the phosphor in the preferably mirrored, deep-drawn depression also causes an increase in the conversion efficiency.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2010/0245777 A1 [0003]
• US 2010/0328617 A1 [0007]

Claims (12)

Fluorescent wheel ( 12 ) for a lighting device ( 1 ) for the conversion of excitation radiation ( 4 ) in conversion light designed for rotation about an axis of rotation (A), comprising - a disc-shaped carrier substrate ( 120 ) with a front ( 130 ) and a back ( 150 ) and - at least one on a front side ( 130 ) of the carrier substrate ( 120 ) and with excitation radiation ( 4 ) irradiable phosphor region ( 140 . 180 ), wherein the phosphor region ( 140 . 180 ) through a depression ( 140 ) in the front ( 130 ) of the carrier substrate ( 120 ) and wherein in the recess ( 140 ) at least one phosphor layer ( 180 ), characterized in that the depression ( 140 ) is formed by deep drawing. Fluorescent wheel ( 12 ) according to claim 1, wherein the recess ( 140 ) is formed annular or circular segment. Fluorescent wheel ( 12 ) according to claim 2, wherein the cross-sectional area of the recess ( 140 ) is trapezoidal or circular section shaped. Fluorescent wheel ( 12 ) according to one of the preceding claims, wherein the carrier substrate ( 120 ) is designed as a mirrored metal disc. Fluorescent wheel ( 12 ) according to any one of the preceding claims, wherein the phosphor layer ( 180 ) just with at least the immediately surrounding surface of the carrier substrate ( 120 ) is trained. Fluorescent wheel ( 12 ) according to any one of the preceding claims, wherein the phosphor concentration (M2) towards the bottom ( 170 ) of the depression ( 140 ) increases. Lighting device ( 1 ), with at least one phosphor wheel ( 12 ) according to one of the preceding claims and at least one excitation radiation source ( 2 ), in particular semiconductor light source, for irradiating the phosphor wheel ( 12 ) with excitation radiation ( 4 ), which by means of the at least one phosphor region ( 140 . 180 ) of the phosphor wheel ( 12 ) is at least partially wavelength convertible in conversion light. Method for producing a phosphor wheel ( 12 ) according to one of claims 1 to 6 with the following method steps: A) providing a first planar carrier substrate, B) forming at least one depression in the carrier substrate by deep drawing, C) embedding at least one phosphor layer in the depression. Method according to claim 8, wherein method step C) comprises the following substeps: C1) providing a mixture of phosphor and carrier matrix, C2) filling the mixture into the depression, C3) compacting the phosphor towards the bottom of the well, C4) drying the phosphor layer in the recess. The method of claim 9, wherein the compacting of the phosphor in step C3 is carried out by means of vibrating or centrifugal compressing. The method of claim 8, 9 or 10 with the following additional process step after process step A): Mirroring the carrier substrate. Method according to one of claims 8 to 10, wherein during the process step B) provided for the bottom of the recess portion of the support substrate between two plane-parallel surfaces of the deep drawing tool is clamped.

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