Abstract
A phosphor composition may include first and second phosphors configured to emit light of a first and a second unsaturated color, respectively. The first unsaturated color may be associated with a first position in a CIE standard color chart adjacent to and above a position of a selected target color of the phosphor composition in the CIE standard color chart. The second unsaturated color may be associated with a second position in a CIE chromaticity diagram adjacent to and below the position of the selected target color of the phosphor composition in the CIE chromaticity diagram. Thereby, the position of the selected target color of the phosphor composition in the CIE chromaticity diagram may be located in an area defined by corner positions R=(cx; cy) given by R1=(0.645; 0.335), R2=(0.665; 0.335), R3=(0.735; 0.265), and R4=(0.721; 0.259).
Claims
1. A phosphor mixture configured for a conversion layer coated on a semiconductor light source, wherein the phosphor mixture comprises: a first phosphor adapted to emit light of a first unsaturated color when irradiated with light from the semiconductor light source and when provided as the only phosphor in the conversion layer, wherein the first unsaturated color is associated with a first position in a CIE chromaticity diagram adjacent to and above a position of a selected target color of the phosphor composition in the CIE chromaticity diagram; a second phosphor adapted to emit light of a second unsaturated color when irradiated with light from the semiconductor light source and when provided as the only phosphor in the conversion layer, the second unsaturated color being associated with a second position in a CIE chromaticity diagram adjacent to and below the position of the selected target color of the phosphor composition in the CIE chromaticity diagram; and wherein the position of the selected target color of the phosphor composition in the CIE chromaticity diagram is in an area defined by corner positions R=(cx; cy) given by R1=(0,645; 0,335), R2=(0,665; 0,335), R3=(0.735; 0.265), and R4=(0,721; 0,259).
2. The phosphor mixture according to claim 1, wherein the phosphor mixture is adapted to emit light of the selected target color associated with the position in the CIE chromaticity diagram when irradiated with light from the semiconductor light source and provided in the conversion layer, the position having a degree of saturation represented by a distance from a closest spectral color greater than a corresponding degree of saturation of the first unsaturated color and the second unsaturated color.
3. The phosphor mixture according to claim 1, wherein: the first phosphor is adapted, when irradiated with light by the semiconductor light source, to emit light having a first spectrum exhibiting light emission in a first wavelength range; said second phosphor is adapted, when irradiated with light by said semiconductor light source, to emit light having a second spectrum exhibiting light emission in a second wavelength range, said second wavelength range being different from said first wavelength range; wherein the first wavelength region overlaps the second wavelength region at least in an interval ranging from about 600 nm to about 700 nm.
4. The phosphor mixture according to claim 3, wherein maximum values of the first and second spectra are each at wavelengths; independently, ranging from 600 nm to 700 nm.
5. The phosphor mixture according to claim 3, wherein the second phosphor is adapted to absorb and filter light in a portion of the first wavelength range that extends adjacent to the lower limit thereof.
6. The phosphor mixture according to claim 5, wherein the second phosphor is adapted to absorb and filter light in an interval of the first wavelength ranging from about 500 to about 580 nm.
7. The phosphor mixture according to claim 1, wherein the semiconductor light source is configured to emit blue light.
8. The phosphor mixture according to claim 7, wherein the semiconductor light source is configured to emit light in a wavelength ranging from 447.5 nm to 450 nm.
9. The phosphor mixture according to claim 7, wherein: a thickness of the phosphor mixture ranges from 30 μm to 70 μm; and a median value of the particle size D50 in the phosphor mixture ranges from 5 μm to 20 μm.
10. The phosphor mixture according to claim 9, wherein the second phosphor, when provided as a single phosphor in the conversion layer and irradiated by the semiconductor light source, is adapted to emit light of a second unsaturated color associated with a position in a CIE standard chromaticity diagram having a basic color component of green of cy≤0.324.
11. The phosphor mixture according to claim 9, wherein the first phosphor, when provided as a single phosphor in a conversion layer and irradiated by the semiconductor light source, is adapted to emit light of a first unsaturated color associated with a position in a CIE standard chromaticity diagram having a fundamental color component of green of cy≥0.328.
12. The phosphor mixture according to claim 9, wherein the phosphor mixture is configured, when irradiated by the semiconductor light source, to emit light of the selected target color associated with a position in the CIE chromaticity diagram corresponding to a saturation level represented by a distance≤0.012 in the cx direction from the nearest spectral color.
13. The phosphor mixture according to claim 1, wherein a mixing ratio in the mixture between the first phosphor and the second phosphor ranges from 75:25 to 55:45.
14. The phosphor mixture according to claim 1, wherein the phosphor composition is configured as a platelet formed from crystals pressed in a ceramic matrix or configured as particles embedded in a silicone layer and demoulded therein.
15. The phosphor mixture according to claim 1, wherein each of the first phosphor and the second phosphor comprises particles corresponding to phosphors from the class of europium-activated strontium calcium alumonitride silicates.
16. A semiconductor light source comprising the phosphor mixture according to claim 1, wherein the semiconductor light source is adapted to emit light in a wavelength ranging from 380 nm to 480 nm, and wherein the phosphor mixture is coated on a light emitting surface of the semiconductor light source.
17. A vehicle lamp comprising the semiconductor light source according to claim 16.
18. The vehicle lamp of claim 17, wherein the vehicle lamp is adapted to be mounted in a brake light, tail light, or rear fog light lighting device.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0052] Further advantages, advantageous embodiments and further developments will become apparent from the non-limiting embodiments described below in connection with the figures.
[0053] FIG. 1 depicts a schematic representation of the CIE standard color chart (CIE 1931), with the ECE-compliant area for red brake lights, taillights and rear fog lights (ECE Regulation 48) entered at the bottom right;
[0054] FIG. 2 depicts an enlarged section of the CIE standard color chart from FIG. 1 with measured color locations for a first phosphor (viewed individually), for a second phosphor (viewed individually) and for a phosphor mixture of the two phosphors for different layer thicknesses of the conversion layer in question;
[0055] FIG. 3 depicts the behavior in the cx direction for the first phosphor (QL916), the second phosphor (QL906) and for the phosphor mixture of both (in a ratio of 70:30) as a function of the dispensing quantity M used to build up the conversion layer, whereby scatter in the measured values was also taken into account in each case;
[0056] FIG. 4 is similar to FIG. 3, but for the behavior in cy direction;
[0057] FIG. 5 depicts the dependence of the photometric luminous flux Φ.sub.v on the dispensing amount M for a first phosphor (QL916), a second phosphor (QL906) and for the phosphor mixture of both (in the ratio 70:30);
[0058] FIG. 6 depicts the correlation of luminous flux Φ.sub.v with temperature T for the first phosphor (QL916), the second phosphor (QL906), and for the phosphor mixture of both (in the ratio 70:30);
[0059] FIG. 7 depicts a measurement series of the chromaticity coordinates in the CIE standard chromaticity diagram for different temperatures T. For the first phosphor (QL 916), the second phosphor (QL 906) and the phosphor mixture, measurement series are shown for different dispensing amounts M of 6.5 mg and for a dispensing amount M of 7.0 mg, respectively;
[0060] FIG. 8 depicts the recorded spectra of the pure substances (first phosphor: Bz. 230, and second phosphor: Bz. 240) in comparison with each other (photometric luminous flux Φ.sub.v plotted against wavelength λ), with the actual spectrum convolved with the eye sensitivity;
[0061] FIG. 9 is similar to FIG. 8, but in an integrated representation.
[0062] In the non-limiting embodiments and figures, identical elements, elements of the same kind or elements having the same effect may each be provided with the same reference signs. The elements shown and their proportions to one another are not necessarily to be regarded as true to scale; rather, individual elements may be shown exaggeratedly large for better representability and/or better understanding.
DETAILED DESCRIPTION
[0063] In the following description, it should be appreciated that the present disclosure of the various aspects is not limited to the details of the structure and arrangement of the components as shown in the following description and figures. The embodiments may be put into practice or carried out in various ways. It should further be appreciated that the expressions and terminology used herein are used for the purpose of specific description only, and these should not be construed as such in a limiting manner by those skilled in the art.
[0064] A non-limiting embodiment is described with reference to FIGS. 1 to 2. FIG. 1 shows in schematic representation the graphical reproduction of the general CIE standard color chart 10 (CIE 1931, 2° field of view), with an ECE-compliant area 20 for red brake lights, tail lights and rear fog lights (ECE regulation 48) entered at the bottom right. On the abscissa (x-axis), the proportion between 0 and 1 of the basic color red (700 nm) is plotted as cx, while the ordinate (y-axis) represents with cy the proportion between 0 and 1 of the basic color green (546.1 nm). The third dimension of this diagram, which points out of the drawing plane, is not shown and represents the value cz between 0 and 1, which reflects the proportion of the primary color blue (435.8 nm). With these 3 primary colors, all colors visually detectable by the human eye can be assigned to exactly one proportion combination in superposition. The cx-cy plane in the diagram represents a kind of projection plane from three-dimensional space.
[0065] The horseshoe-shaped outer edge represents the spectral color line 12 with spectral colors from red to yellow and from green to blue. These correspond to monochromatic light emission at the wavelengths shown in FIG. 1. The spectral colors correspond to ultra-pure colors with full saturation. The horseshoe is bounded at the bottom by the so-called purple line 16, which is drawn linearly from a point corresponding to the color blue at 380 nm to a point corresponding to the color red at 700 nm. Towards the center of the diagram, there are color mixtures that extend from unsaturated hues on the outside to white hues on the very inside. Also entered for purely illustrative purposes is a line 14 resulting for black bodies of different temperatures, with temperatures entered as examples in each case.
[0066] According to ECE Regulation 48, red light is mandatory for brake lights, tail lights, rear fog lights, etc., on vehicles. For the purpose of clear differentiation from yellow light (e.g. turn signals) or white light (e.g. low beam), the CIE standard chromaticity diagram specifies an area 20 covering red light that extends (in FIG. 1, bottom right) along a range of red spectral colors (from garnet to deep or purple) with comparatively high saturation. The degree of saturation corresponds to a distance of a chromaticity point in the CIE chromaticity diagram from a nearest spectral color. The corresponding direction is nearly parallel to the cx-axis (i.e., the red component). The area is defined by four corner positions R=(cx; cy), define a very narrow, square, almost parallelogram-like strip. The four corner positions are given by: [0067] R1=(0,645; 0,335), [0068] R2=(0,665; 0,335), [0069] R3=(0.735; 0.265), and [0070] R4=(0,721; 0,259).
[0071] In FIG. 2, an enlarged section of the CIE standard color chart of FIG. 1 is shown with measured color locations for a first phosphor (viewed individually), for a second phosphor (viewed individually) and for a phosphor mixture of the two phosphors for different layer thicknesses of the conversion layer in question. The area 20 is shown only with respect to its upper part, wherein a sub-area 21 with corner positions R1, R2, R3′ and R4′ is defined, denoted “dry red”, and is a working area for the present embodiment. The lower corner positions R3′=(0.680; 0.320) and R4′=(0.660; 0320), which define the lower limit of this “dry red”, are significantly higher than the corner positions R3 and R4. The area below the exposures R3′ and R4′ is therefore less relevant, because here the physical emission spectrum is already very strongly affected by a convolution with the sensitivity curve of the human eye.
[0072] The phosphor mixture is composed of a first phosphor of the type QL916, manufactured and distributed in the group of companies of the applicant and a second phosphor of the type QL906, also manufactured and distributed in the group of companies of the applicant. As described at the beginning, these are from the class of europium-activated strontium-calcium-alumonitride silicates or those with the chemical abbreviation Sr(Sr,Ca)Si2Al2N6:Eu2+, which have been known as such since 2016 at the latest (for reference see above). They differ in structural parameters such as particle sizes or element ratios, so that the color locations of the two phosphors achieved in emission in the CIE standard chromaticity diagram have a vertical difference in the cy direction (green component) of more than 0.005 (for the same conversion factor) (see FIG. 2). In the embodiment example, they are mixed in a mass ratio of 70:30. The semiconductor light source used is an LED chip with a 1 mm.sup.2 light-emitting surface, which, when supplied with power, emits blue light in a wavelength range from 447.5 nm to 450 nm. A conversion layer containing the phosphor mixture is formed on the light-emitting surface. A median value of the particle sizes D50 in both phosphors is between 5 μm and 20 μm. For production, the particles of the two phosphors are mixed and embedded in liquid silicone. In this, the particles are sedimented and the silicone hardens. The thickness of the silicone layer is 200 to 300 μm, but the backfill height of the phosphor particles after sedimentation is only between 30 and 70 μm including the limits. This is the effective thickness of the conversion layer considered here. Finally, the conversion layers are cut out of the silicone layer in a suitable size and glued onto the light-emitting surface of the semiconductor light sources.
[0073] The backfill height or the thickness of the conversion layer determines the degree of conversion of the light scattered from the semiconductor light source into the phosphor mixture (from blue to red). The thicker the conversion layer, the stronger the conversion. In the series of measurements shown in FIG. 2, however, it is not the thickness of the conversion layer that is indicated, but rather the corresponding dispensing weight (in milligrams mg), which reflects the mass of the phosphor added to the silicone and sedimented there, whereby this here refers to an entire panel with several semiconductor light sources.
[0074] FIG. 2 shows the results for the first phosphor and the second phosphor for the case in which they are present alone, i.e. not as a mixture, in a conversion layer. Series of measurements were taken for dispensing weights of 6.0 mg, 6.5 mg, 7.0 mg, 7.5 mg, 8.0 mg, 8.5 mg, 9.0 mg and 9.5 mg, i.e. 7 measured values each. The color locus for the light from the semiconductor light source with the first or second phosphor at a dispensing weight of 6.0 mg is on the left side in the CIE standard chromaticity diagram, i.e., at lower value cx, i.e., at low color saturation, because conversion is still lowest here and a considerable proportion of the blue light emitted by the semiconductor light source contributes to the spectrum. For higher dispensing weights in each case, the respective color locations for each phosphor follow one after the other towards higher values of cx.
[0075] The first phosphor is a phosphor already used for brake, tail and rear fog lamps and emits in the garnet color range. In FIG. 2, the measurement series (chromaticity coordinates 30 for the first phosphor) is represented by squares. As can be seen, at a low dispensing weight of 6.0 mg, the color location of the combined emission from the semiconductor light source and the first phosphor lies outside the ECE-compliant area 20 or 21 for red light in vehicle lighting. Only from 6.5 mg dispensing weight is the conversion sufficient to achieve just adequate saturation.
[0076] The same applies to the second phosphor, whose emission is already in the deep purple range and which is subject to greater fluctuations in luminous flux as the temperature varies, which is why this phosphor is intrinsically less suitable for use in generating red light in vehicle lamps. In FIG. 2, the corresponding series of measurements (chromaticity coordinates 40 for the first phosphor) is represented by circles. Here, too, the chromaticity coordinates of the combined emission from the semiconductor light source and the second phosphor are outside the ECE-compliant range at a low dispensing weight of 6.0 mg, and sufficient color saturation is obtained only from a dispensing weight of 6.5 mg.
[0077] The corresponding results of the measurement series (color locations 50) for the phosphor mixture of the embodiment are shown as diamonds in FIG. 2. The series begins on the left with the color location for the light emission from the combination of semiconductor light source and phosphor mixture with a dispensing weight of 6.0 mg. Here it is already remarkable that the first measuring point lies within area 20 for an ECE-compliant red light. If the two corresponding points of the measurement series for the first phosphor (square lying furthest to the left in FIG. 2) and the second phosphor (circle lying furthest to the left) are connected by a line, the corresponding point (color location) for the phosphor mixture (diamond lying furthest to the left) lies very clearly to the right of the line, i.e. in an area of significantly improved saturation compared with both phosphors considered individually. Conventionally expected for simple color mixing, a color locus would be approximately at (cx=0.65; cy=0.325) when considering the 70:30 mixing ratio. However, these observations continue slowly weakening for higher dispensing weights. However, it can be seen that from about 8.0 mg dispensing weight, full conversion seems to occur in all 3 cases (phosphors individually irradiated and phosphor mixture) and hardly any improvements in color saturation are achieved. Here, the three color locations lie on one line, so that simple color mixing is present in a ratio of 70:30 (see the points farthest to the right of the 3 measurement series, corresponding to 9.5 mg dispensing weight.
[0078] In summary, however, it can be stated that the color locations are much closer together in the phosphor mixture, so that noticeable color fluctuations (degree of saturation) during operation and between different batches are significantly reduced, and that color saturations in the permissible range are obtained even at lower dispensing weights.
[0079] FIGS. 3 to 9 illustrate the findings on the basis of measurements carried out in the embodiment. FIGS. 3 and 4 show the behavior in cx and cy for the first phosphor (QL916), the second phosphor (QL906, considered individually in each case) and for the phosphor mixture of both (in the ratio 70:30) as a function of the dispensing quantity M used to build up the conversion layer, whereby, in contrast to FIG. 2, scatter in the measured values was also taken into account in each case.
[0080] It can be seen that, with regard to the red component cx of the emitted and transmitted light, the color locations 50 are significantly closer together in the case of the phosphor mixture starting at a dispensing amount of 6.0 mg up to 9.0 mg than is the case with the color locations 30 of the first phosphor and 40 of the second phosphor. Also, the dispersion obtained in the phosphor mixture remains comparable to the individual phosphors considered individually.
[0081] With regard to the cy direction (green component of the emitted and transmitted light), a flattening of the curve in the case of the phosphor mixture already occurs between 6.7 and 7.0 mg. This means that an invariance of the green component can already be achieved here at considerably lower dispensing quantities M than in the case of the individual phosphors. Furthermore, the curve is flatter overall. Thus, the desired red component can be effectively achieved with less effect on the green component, even with lower layer thicknesses of the conversion layer. In the embodiment example, the dispensing amount corresponds to a thickness of 30 μm to 70 μm, with a median value of the particle size D50 in the phosphor mixture of between 5 μm and 20 μm.
[0082] FIG. 5 shows the dependence of the photometric luminous flux Φ.sub.v on the dispensing quantity M for the first phosphor (QL916), the second phosphor (QL906, considered individually in each case) and for the phosphor mixture of both (in the ratio 70:30). It can be seen that the scatter of the measured values of series 150 for the phosphor mixture with e.g. 6.5 mg is comparable to the fluctuations for the pure substances, i.e. the measured values 130 for the first phosphor and 140 for the second phosphor (each considered individually), but the luminous flux is not reproduced in the ratio 70:30. The corresponding measured value of row 150 is 111 lm, but at the specified ratio it should be closer to the value of the first phosphor (about 117 lm) than to the value of the second phosphor (about 107 lm). This means a slight loss of luminous flux, but this is acceptable, especially since FIG. 5 shows that the interval of luminous fluxes for dispensing amounts between 6.0 mg and 9.0 mg is smallest for the phosphor mixture.
[0083] FIG. 6 shows a correlation of the luminous flux Φ.sub.v with the temperature T for the first phosphor (QL916), the second phosphor (QL906, each considered individually) and for the phosphor mixture of both (in the ratio 70:30). It can be seen that in all cases the luminous flux drops toward higher temperatures, with the effect as described being most noticeable for the second phosphor (luminous flux measurement series 140, indicated by circles in FIG. 6). The luminous flux measurement series 130 of the garnet-colored first phosphor remains comparatively the most stable, while the luminous flux measurement series 150 for the phosphor mixture lies in between, but is also closer to that of the purple-colored second phosphor.
[0084] The respective series of measurements of the color locations in the CIE standard chromaticity diagram are shown for different temperatures T in FIG. 7. For the first phosphor, the second phosphor and the phosphor mixture, measurement series are shown respectively for a dispensing amount M of 6.5 mg (measurement series 31: first phosphor, 41: second phosphor, 51: phosphor mixture) and for a dispensing amount M of 7.0 mg (measurement series 32: first phosphor, 42: second phosphor, 52: phosphor mixture). These are the potential dispensing amounts for the phosphor mixture as shown above. It can be seen that the “gain” in cy and cx (i.e., a higher degree of saturation) of the phosphor mixture is maintained even at higher temperatures. Only the luminous flux (1)v, as described, is lower than that of the pure phosphor QL916 as the first phosphor, but this is acceptable in view of the enormous advantages obtained with the phosphor mixture. In addition, as can be seen in FIG. 7, not only for all relevant dispensing quantities but also for all possibly occurring temperatures T, the color locations are safely located within the ECE-compliant area 20, which is defined by corner positions R=(cx; cy), which are given by [0085] R1=(0,645; 0,335), [0086] R2=(0,665; 0,335), [0087] R3=(0.735; 0.265), and [0088] R4=(0,721; 0,259).
[0089] FIGS. 8 and 9 serve to explain the filter effect that is exploited here. Shown are the recorded spectra of the pure substances (first phosphor: reference 230, and second phosphor: reference 240) compared to each other (photometric luminous flux Φ.sub.v plotted against wavelength λ), with the actual spectrum convolved with eye sensitivity. It can be seen that the first phosphor (QL916) produces its greater luminous flux in a range of 500-700 nm or more narrowly 550-650 nm. This range also includes the major portion of the light emitted by the second phosphor (QL906), but with the difference that the second phosphor emits hardly any light in a region of the first wavelength range between 500 and 580 nm, i.e., the short-wave flank of the spectrum of the light emitted by the first phosphor. FIG. 9 shows the integrated luminous flux from FIG. 8 in a different illustration to make the difference more visible. Instead of emitting light, the second phosphor absorbs or filters light and reemits it in its emission range above 600 nm. The spectrum thus becomes narrower, the degree of color saturation increases, and the chromaticity coordinate is shifted toward the red.
[0090] It should be noted that the described combination of phosphors is only one of many possibilities, and that the skilled person can also combine other individual phosphors using the described idea to achieve the same effect. It is also possible to combine more than two phosphors. Furthermore, it is also possible to combine phosphors according to the instructions given in the appended claims, which are in no way subject to the loss of luminous flux described in the embodiments and are nevertheless comprised. Furthermore, it is also possible to combine phosphors according to further embodiment examples in which the filtering effect of the phosphor that is weaker in light and subject to greater fluctuations is not so clearly evident.
