High-brightness luminescent-based lighting device

Abstract

The invention provides a lighting device configured to generate lighting device light, wherein the lighting device light includes an emission band in the visible part of the spectrum which represents at least 80% of the total power (W) of the lighting device light in the visible part of the spectrum, wherein the emission band has a full width half maximum of at maximum 60 nm, and wherein the emission band has a peak maximum (MM3), wherein said emission band includes luminescent material light, wherein the lighting device includes (i) a solid state-based light source, configured to generate light source light having a peak maximum (MX2), and (ii) a luminescent material, configured to convert at least part of the light source light into said luminescent material light, wherein the solid state-based light source is configured to provide said light source light with 0<MM3MX2<60 nm.

Claims

1. A lighting device comprising: a solid-state-based light source configured to generate light source light having a peak maximum; and a luminescent material positioned downstream from the solid-state-based light source and configured to convert at least part of the light source light into luminescent material light; wherein the luminescent material light includes an emission band in the visible part of the spectrum which represents at least 80% of the total power of the luminescent material light in the visible part of the spectrum, the emission band having a full width half maximum of at maximum 60 nm, and the emission band having a peak maximum; wherein the wavelength of the peak maximum of the light source light subtracted from the wavelength of the peak maximum of the emission band is great-than-or-equal to 0 nm and less-than-or-equal to 60 nm; and wherein the lighting device is configured to provide the luminescent material light with a radiance of at least 2 W/(sr.Math.mm.sup.2).

2. The lighting device according to claim 1, further comprising a converter comprising the luminescent material, wherein the solid-state-based light source and the luminescent material are selected to provide the luminescent material light with an energy conversion loss of at maximum 13%, and wherein the wavelength of the peak maximum of the light source light subtracted from the wavelength of the peak maximum of the emission band is greater-than-or-equal-to 5 nm and less-than-or-equal to 30 nm.

3. The lighting device according to claim 1, further comprising a converter comprising the luminescent material and a converter surface, wherein the lighting device is configured to provide the light source light to the converter surface with a power of at least 1 W/cm.sup.2.

4. The lighting device according to claim 1, wherein the solid-state-based light source comprises a laser.

5. The lighting device according to claim 1, further comprising a luminescent concentrator comprising the luminescent material.

6. The lighting device according to claim 1, further comprising a spot of luminescent material, wherein the spot has an area of at maximum 1 mm.sup.2.

7. The lighting device according to claim 1, wherein the luminescent material comprises luminescent quantum dots based on one or more of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe and HgZnSTe type quantum dots.

8. The lighting device according to claim 1, wherein the luminescent material comprises luminescent quantum dots based on one or more of CdSe and CdS.

9. The lighting device according to claim 1, wherein the luminescent material comprises luminescent quantum dots based on one or more of InP, CuInS.sub.2 and AgInS.sub.2 type quantum dots.

10. The lighting device according to claim 1, wherein the luminescent material has a Stokes shift, less-than-or-equal-to 60 nm.

11. The lighting device according to claim 1, wherein the solid-state-based light source and the luminescent material are selected to provide the luminescent material light with an energy conversion loss of at maximum 10%.

12. A lighting apparatus comprising the lighting device according to claim 1.

13. The lighting apparatus according to claim 12, further comprising one or more further lighting devices, wherein the lighting device and the one or more further lighting devices are configured to provide white light.

14. The lighting apparatus according to claim 13, wherein the one or more further lighting devices comprise.

15. The lighting device according to claim 1, wherein the lighting device is configured to generate lighting device light, the lighting device light comprising the luminescent material light and some of the light source light.

16. The lighting device according to claim 15, wherein 80% or more of the power of the light source light is from the luminescent material light.

17. The lighting device according to claim 1, further comprising a light exit window positioned downstream from the solid-state-based light source.

18. The lighting device according to claim 17, wherein the light exit window comprises a light transmissive solid material.

19. The lighting device according to claim 17, wherein the luminescent material is positioned upstream of the light exit window.

20. The lighting device according to claim 17, wherein the light exit window comprises the luminescent material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

(2) FIGS. 1a-1e schematically depict some aspects of the invention;

(3) FIG. 2 shows an excitation and an emission spectrum of a quantum dot, including light source light;

(4) FIGS. 3a-3e schematically depict some aspects of the invention, especially embodiments of the lighting device;

(5) FIGS. 4a-4d schematically depict some aspects of the invention, especially embodiments of the lighting apparatus;

(6) FIGS. 5a-5c schematically depict some further aspects of the invention; and

(7) FIGS. 6a-6d show emission spectra of InP QD, CdSe Qd, CdTe QD, and CdTe QD (larger particles than the former).

(8) The schematic drawings are not necessarily on scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(9) FIG. 1a schematically depicts an embodiment of a lighting device 100 configured to generate lighting device light 101. The lighting device 100 comprises a solid state-based light source 10, configured to generate light source light 11, and a luminescent material 20, configured to convert at least part of the light source light 11 into luminescent material light 21. The light downstream of the luminescent material 20 is indicated with reference 101. The light 101 at least comprises the emission or luminescence of the luminescent material 20, i.e. the luminescent material light 21. Optionally, some of the light source light 11 might also be comprised by the lighting device light 101. This may not be a problem, as the wavelength of the light source light and the luminescent material light may be substantially identical.

(10) Especially, the lighting device light 101 substantially consists of the luminescent material light 21, such as 80% or more, such as at least 90% of the power (W) of the emission band may be luminescent material light.

(11) The light source 10 is configured upstream of the luminescent material 20, the luminescent material light 21 emanates downstream from said luminescent material. Especially, herein transmissive configuration are applied. The terms upstream and downstream relate to an arrangement of items or features relative to the propagation of the light from a light generating means (here the especially the first light source), wherein relative to a first position within a beam of light from the light generating means, a second position in the beam of light closer to the light generating means is upstream, and a third position within the beam of light further away from the light generating means is downstream. Here, by way of example a transmissive configuration is depicted. However, as indicated below, also reflective configurations may be chosen.

(12) The lighting device light 101 includes an emission band 110 in the visible part of the spectrum, see FIGS. 1b-1c. Especially, this band represents at least 80% of the total power W of the lighting device light 101 in the visible part of the spectrum. The emission band 110 has full width half maximum FWHM of at maximum 1500 cm.sup.1. The luminescent material 20 is a small-Stokes shift material having a Stokes shift SS of the luminescent material light 21 and a corresponding lowest energy excitation band EX of at maximum 1500 cm.sup.1 (note that here by way of example the excitation spectrum has two excitation maxima; for a calculation of the Stokes shift, the lowest band in energy is chosen, as known in the art). As shown in FIG. 1b, the solid state-based light source 10 is configured to provide the light source light 11 at a wavelength within the lowest energy excitation band EX leading to irradiance of at least 10 W/(cm.sup.2) on the luminescent material 20. The emission (band) of the luminescent material is also indicated with reference EM. The difference in peak maximum MM3 of the emission band 21/EM and the peak maximum MX2 of the light source light 11 is indicated with reference SS2. Especially, the difference SS2 is larger than 0 nm, but equal to or smaller than 30 nm. FIG. 1c shows the lighting device light 101, which may thus substantially consist of the luminescent material light 21.

(13) FIG. 1d schematically depicts an embodiment of the lighting device 100 further comprising a luminescent concentrator 50 comprising the luminescent material 20, wherein the light source light 11 enters the concentrator 50 at surface 201 and exits the concentrator at a surface substantially perpendicular to and having a smaller area than the surface 201 thereby providing high intensity light. Embodiments of the luminescent concentrator are described further below. FIG. 1e schematically depicts an embodiment of the lighting device 100 comprising a spot 60 of luminescent material 20, wherein the spot 60 has an area of e.g. at maximum 1 mm.sup.2, or even smaller. The dimensions of the spot are by way of example indicated with L/W/D, indicating the length and width, or the diameter, whatever may be applicable. The spot 60 may have any (cross-sectional) shape, such as round, square, rectangular, oval, etc., but especially round (with dimension D), or square (with dimension L=W). Reference 200 indicates a converter 50 comprising luminescent material 20, or the spot 60 of comprising luminescent material 20, and reference 201 indicates a converter surface, i.e. a surface of the converter at which the solid state-based light source may irradiate its light 11.

(14) FIG. 2 schematically depicts an excitation (EX) and emission (EM) spectrum of a CdSe tetrapod quantum dot emission at about 630 nm (FWHM less than 30 nm), as well as the emission (light source light 11) of a narrow band excitation source at 620 nm. The Stokes shift is indicated with reference SS. As can be seen, the Stokes shift is very small, in the order of only 10 nm, this leads to Stokes-shift related energy loss of 4.5%. Note that in this embodiment the excitation maximum MX1 and the light source light maximum MX2 are chosen to be substantially identical. However, this is not necessarily the case (see also FIG. 1b). For instance, the light source may be configured to excite the luminescent material at a longer wavelength, when desired (i.e. a lower Stokes-shift related energy loss). As shown in this figure, the solid state-based light source is configured to provide said light source light 11 with 0<MM3MX260 nm.

(15) For various applications such as projection, stage lighting and automotive headlamps it is desirable to have high intensity light sources.

(16) Such light sources can be based on laser light or luminescent concentrator based concepts. However, in the case of using lasers coherence and eye safety is an issue. For that reason it is desirable to convert the laser light to other wavelengths. During the conversion large amount of heat produced is in a small volume which leads to a temperature rise. In the same way luminescent concentrator based light sources need to be cooled effectively in order to avoid thermal quenching. As a result of cooling surfaces the efficiency is reduced considerably.

(17) Here, we suggest (thus) using narrow emitters and pump these at a wavelength which leads to a low Stokes losses minimizing energy loss and hence temperature increase. For this purpose, materials such as quantum dots (QDs) can be used (see also FIG. 2). The shift in wavelength between absorption and emission of the narrow emitter is especially below 20 nm, more especially below 10 nm, and most especially below 5 nm. Here below various specific lighting configurations will be described. The full width half max of a quantum dot is about 20 nm. Thus this QDs can be pumped with e.g. laser diode or LED with a FWHM of typically 2 nm and 20 nm, respectively.

(18) In an embodiment, we suggest a lighting device comprising a laser diode and a phosphor material (see also for instance FIG. 1e). The phosphor material absorbs laser light and emits converted laser light.

(19) The narrow band emitter may be partly enclosed by a reflective heat sink 77 (FIG. 3a). In another configuration, we suggest the use of the converter 200 with the reflective heat sink 77 in the reflective mode (FIG. 3b). In another embodiment, we suggest the use of multiple lasers (as solid state light sources 10) pumping the same converter 200 (or luminescent element) and with the reflective heat sink 77 (FIG. 3c).

(20) In yet another embodiment, we suggest a laser based lighting device comprising a luminescent material in a light guide. Laser light is pumping the phosphor 20 in the light guide, i.e. a luminescent concentrator. See further also below with respect to a luminescent concentrator. The phosphor is converting at least a part of the light with the first spectral distribution to light with a second spectral distribution, guiding the light with the second spectral distribution to the first light exit surface and coupling the light with the second spectral distribution out of the first light exit surface wherein the luminescent wherein the shift in wavelength between absorption and emission of the narrow emitter is especially below 20 nm, more especially below 10 nm, and most especially below 5 nm (FIG. 3d).

(21) In another embodiment, we suggest a light emitting device comprising a light source adapted for, in operation, emitting light with a first spectral distribution, a first luminescent light guide comprising a first light input surface and a first light exit surface extending at an angle different from zero to one another, and the first luminescent light guide being adapted for receiving the light with the first spectral distribution at the first light input surface, converting at least a part of the light with the first spectral distribution to light with a second spectral distribution, guiding the light with the second spectral distribution to the first light exit surface and coupling the light with the second spectral distribution out of the first light exit surface wherein the luminescent wherein the shift in wavelength between absorption and emission of the narrow emitter is especially below 20 nm, more especially below 10 nm, and most especially below 5 nm (FIG. 3e).

(22) In yet another embodiment, we suggest a lighting device comprising more than one phosphor material and pump the phosphor materials with different lasers to obtain white light (FIG. 4a). This figure schematically depicts an embodiment of a lighting apparatus 1000. References 20a-20c indicate different types of luminescent materials, providing different types of light (see also FIG. 4c). Light generated by the apparatus 1000 is indicated with reference 1001.

(23) In yet another embodiment, we suggest the use of the light emitting device in combination with other solid state lighting light sources 1100 such as light emitting diodes (LEDs) or laser diodes. In a preferred embodiment, the light emitting device is combined with light sources emitting different colors to obtain white light (FIG. 4b).

(24) In yet another embodiment, several light emitting devices might be combined (FIG. 4c). In yet another embodiment, several light emitting devices might be combined in series. Light absorption is prevented by adding dichroic mirrors between the luminescent sections (FIG. 4d). References 21a-21c indicate different types of luminescent materials light, provided by different types of luminescent materials 20a-20c, respectively. In FIGS. 4c-4d in fact three lighting device 100 are depicted, indicated with references 100a-100c. Reference M indicates a mirror.

(25) A lamp, a luminaire, and a lighting system comprising a light emitting device as defined herein may be used in one or more of the following applications: digital projection, automotive lighting, stage lighting, shop lighting, home lighting, accent lighting, spot lighting, theater lighting, fiber optic lighting, display systems, warning lighting systems, medical lighting applications, decorative lighting applications. In yet another embodiment, we suggest the use of the lighting device in a lamp, a luminaire or lighting system. In yet another embodiment, we suggest the use of the lighting device in a projector system.

(26) Materials such as quantum dots (QDs) can be used. The shift in wavelength between absorption and emission of the narrow emitter is especially below 20 nm, more especially below 10 nm, and most especially below 5 nm.

(27) Quantum dots (or rods) are small crystals of semiconducting material generally having a width or diameter of only a few nanometers. When excited by incident light, a quantum dot emits light of a color determined by the size and material of the crystal. Light of a particular color can therefore be produced by adapting the size of the dots. Most known quantum dots with emission in the visible range are based on cadmium selenide (CdSe) with shell such as cadmium sulfide (CdS) and zinc sulfide (ZnS). Cadmium free quantum dots such as indium phosphide (InP), and copper indium sulfide (CuInS.sub.2) and/or silver indium sulfide (AgInS.sub.2) can also be used. Quantum dots show very narrow emission band and thus they show saturated colors. Furthermore the emission color can easily be tuned by adapting the size of the quantum dots. Any type of quantum dot known in the art may be used in the present invention. However, it may be preferred for reasons of environmental safety and concern to use cadmium-free quantum dots or at least quantum dots having a very low cadmium content.

(28) Embodiments of luminescent concentrator are further described below. An embodiment of the luminescent concentrator as defined herein is schematically depicted in FIG. 5a. FIG. 5a schematically depicts a lighting device 100 comprising a plurality of solid state light sources 10 and a luminescent concentrator 50, such as an elongated (ceramic) body having a first face 141 and a second face 142 defining a length L of the (elongated) concentrator body 50. The (elongated) concentrator body 50 comprises one or more radiation input faces 111, here by way of example two oppositely arranged faces, indicated with references 143 and 144 (which define e.g. the width W). Further the concentrator body 50 comprises a radiation exit window 112, wherein the second face 142 comprises said radiation exit window 112. The entire second face 142 may be used or configured as radiation exit window. The plurality of solid state light sources 10 are configured to provide (blue) light source light 11 to the one or more radiation input faces 111. As indicated above, they especially are configured to provide to at least one of the radiation input faces 111 a blue power W.sub.opt of in average especially, but not exclusively, at least 0.067 Watt/mm.sup.2.

(29) The (elongated) concentrator body 50 may comprises a ceramic material 120 configured to wavelength convert at least part of the (blue) light source light 11 into converter light 101, such as at least one or more of green and red converter light 101. References 720 and 721 indicate an optical filter and a reflector, respectively. The former may reduce e.g. non-green light when green light is desired or may reduce non-red light when red light is desired. The latter may be used to reflect light back into the concentrator body or waveguide, thereby improving the efficiency. Note that more reflectors than the schematically depicted reflector may be used.

(30) The light sources may in principle be any type of point light source, but is in an embodiment a solid state light source such as a Light Emitting Diode (LED), a Laser Diode or Organic Light Emitting Diode (OLED), a plurality of LEDs or Laser Diodes or OLEDs or an array of LEDs or Laser Diodes or OLEDs, or a combination of any of these.

(31) FIGS. 5a-5b schematically depict similar embodiments of the lighting device. Further, the lighting device may include further optical elements, either separate from the waveguide and/or integrated in the waveguide, like e.g. a light concentrating element, such as a compound parabolic light concentrating element (CPC). The lighting devices 1 in FIG. 5b further comprises a collimator 24, such as a CPC.

(32) FIG. 5c schematically depicts some embodiments of possible concentrator bodies as waveguides or luminescent concentrators. The faces are indicated with references 141-146. The first variant, a plate-like or beam-like concentrator body has the faces 141-146. Light sources, which are not shown, may be arranged at one or more of the faces 143-146. The second variant is a tubular rod, with first and second faces 141 and 142, and a circumferential face 143. Light sources, not shown, may be arranged at one or more positions around the concentrator body. Such concentrator body will have a (substantially) circular or round cross-section. The third variant is substantially a combination of the two former variants, with two curved and two flat side faces. The variants shown in FIG. 5c are not limitative. More shapes are possible, i.e. for instance referred to WO2006/054203, which is incorporated herein by reference. The concentrator bodies, which are used as light guides, generally may be rod shaped or bar shaped light guides comprising a height H, a width W, and a length L extending in mutually perpendicular directions and are in embodiments transparent, or transparent and luminescent. The light is guided generally in the length L direction. The height H is in embodiments <10 mm, in other embodiments <5 mm, in yet other embodiments <2 mm. The width W is in embodiments <10 mm, in other embodiments <5 mm, in yet embodiments <2 mm. The length L is in embodiments larger than the width W and the height H, in other embodiments at least 2 times the width W or 2 times the height H, in yet other embodiments at least 3 times the width W or 3 times the height H. Hence, the aspect ratio (of length/width) is especially larger than 1, such as equal to or larger than 2. Unless indicated otherwise, the term aspect ratio refers to the ratio length/width.

(33) The aspect ratio of the height H:width W is typically 1:1 (for e.g. general light source applications) or 1:2, 1:3 or 1:4 (for e.g. special light source applications such as headlamps) or 4:3, 16:10, 16:9 or 256:135 (for e.g. display applications). The light guides generally comprise a light input surface and a light exit surface which are not arranged in parallel planes, and in embodiments the light input surface is perpendicular to the light exit surface. In order to achieve a high brightness, concentrated, light output, the area of light exit surface may be smaller than the area of the light input surface. The light exit surface can have any shape, but is in an embodiment shaped as a square, rectangle, round, oval, triangle, pentagon, or hexagon.

(34) FIGS. 6a-6d show emission spectra upon excitation at 600 nm, with emission at about 650 nm for InP (FIG. 6a), energy loss is 8.2%, with emission at about 630 nm for CdSe (FIG. 6b), energy loss is 5%, and with emission at about 640 nm for CdTe (FIG. 6c), with energy loss is 6.4%. FIG. 6d shows an example where the difference between pump peak maximum (600 nm) and emission maximum is substantially larger. Here, the emission is at 700 nm; the quantum dots are CdTe. The energy loss is 14.4%. The QDs in FIGS. 6c and 6d have particles sizes of about 4.4 and 5 nm, respectively. No pump emission is visible when the absorbance of the quantum dots is high enough, e.g. when the concentration of quantum dots in a matrix is high enough or the layer thickness of the QD material is thick enough.

(35) The term substantially herein, such as in substantially all light or in substantially consists, will be understood by the person skilled in the art. The term substantially may also include embodiments with entirely, completely, all, etc. Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term substantially may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term comprise includes also embodiments wherein the term comprises means consists of. The term and/or especially relates to one or more of the items mentioned before and after and/or. For instance, a phrase item 1 and/or item 2 and similar phrases may relate to one or more of item 1 and item 2. The term comprising may in an embodiment refer to consisting of but may in another embodiment also refer to containing at least the defined species and optionally one or more other species.

(36) Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

(37) The devices herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

(38) It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb to comprise and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article a or an preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

(39) The invention further applies to a device comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings.

(40) The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.