YELLOW EMITTING LUMINOPHORE AND ILLUMINATING DEVICE

Abstract

A luminophore may have the general empirical formula X.sub.3A.sub.4Si.sub.3O.sub.8N.sub.2:E, where: X=Mg, Ca, Sr, Ba, Zn, or combinations thereof; A=Li, Na, K, Rb, Cs, Cu, Ag, or combinations thereof; Z=Al, Ga, B, or combinations thereof; and E=Eu, Ce, Yb, Mn, or combinations thereof.

Claims

1. A phosphor having the general empirical formula X.sub.3X.sub.4Si.sub.3O.sub.8N.sub.2:E, wherein X=Mg, Ca, Sr, Ba, Zn, or combinations thereof; A=Li, Na, K, Rb, Cs, Cu, Ag, or combinations thereof; and E=Eu, Ce, Yb, Mn, or combinations thereof.

2. The phosphor as claimed in claim 1, wherein X=Mg, Ca, Sr, Ba.

3. The phosphor as claimed in claim 1, wherein the general empirical formula is (Ca.sub.1-xX.sup.+.sub.x).sub.3X.sub.4Si.sub.3O.sub.8N.sub.2:E, wherein X.sup.+=Mg, Ba, Sr, or combinations thereof; A=Li, Na, K, Rb, Cs, Cu, Ag, or combinations thereof; E=Eu, Ce, Yb, Mn, or combinations thereof; and 0≤x≤0.25.

4. The phosphor as claimed in claim 3, wherein: X.sup.+=Ba Sr; A=Li, Na, K, Rb, Cs; and 0≤x≤0.25.

5. The phosphor as claimed in claim 1, wherein the general empirical formula is Ca.sub.3X.sub.4Si.sub.3O.sub.8N.sub.2:E, wherein: A=Li, Na, K, Rb, Cs; and E=Eu, Ce, Yb, Mn.

6. The phosphor as claimed in claim 1, wherein A=Li.

7. The phosphor as claimed in claim 1, wherein E=Eu.

8. The phosphor as claimed in claim 1, wherein the phosphor crystallizes in an orthorhombic crystal system.

9. The phosphor as claimed in claim 1, wherein the phosphor crystallizes in an orthorhombic space group Pbcn.

10. An illumination device comprising a phosphor as claimed in claim 1.

11. The illumination device as claimed in claim 10, further comprising: a semiconductor layer sequence configured to emit electromagnetic primary radiation; and a conversion element comprising the phosphor; and wherein the conversion element at least partly converts the electromagnetic primary radiation into electromagnetic secondary radiation.

12. The illumination device as claimed in claim 11, wherein the illumination device is configured to emit an overall white radiation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Further advantageous embodiments and developments arise from the working examples described below in conjunction with the figures. The accompanying drawings serve to afford an understanding of various embodiments. The drawings illustrate embodiments and together with the description serve to elucidate same. Further embodiments and numerous advantages from among those intended are evident directly from the following detailed description. The elements and structures shown in the drawings are not necessarily illustrated in a manner true to scale with respect to one another. Identical reference signs refer to identical or mutually corresponding elements and structures.

[0089] FIGS. 1 and 5 show emission spectra.

[0090] FIG. 2 shows a Kubelka-Munk function.

[0091] FIGS. 3a, 3b, 3c, 3d, 3f, and 3g show sections of the crystal structure of a working example of the phosphor.

[0092] FIG. 4 shows a Rietveld refinement of an X-ray powder diffractogram of a working example of the phosphor.

[0093] FIGS. 6, 7, and 8 show conversion LEDs.

DETAILED DESCRIPTION

[0094] FIG. 1 shows two emission spectra of Ca.sub.3Li.sub.4Si.sub.3O.sub.8N.sub.2:Eu.sup.2+ (WE1). The wavelength in nanometers is plotted on the x axis and the relative intensity in percent on the y axis. For the measurement of the emission spectra, the phosphor was excited both with primary radiation having a peak wavelength of 400 nm and with primary radiation having a peak wavelength of 450 nm. The phosphor has a peak wavelength in the yellow region of the electromagnetic spectrum. On excitation with primary radiation having a peak wavelength of 400 nm, the peak wavelength of the secondary radiation is at 540 nm, the dominant wavelength of the secondary radiation is at 557 nm, the full width at half maximum is 94 nm, and the color locus in the CIE color space is at CIE-x=0.348 and CIE-y=0.555. Excitation with primary radiation having a peak wavelength of 450 nm results in a broadening of the emission band to a full width at half maximum of 100.8 nm. The phosphor may be present as the sole phosphor in an illumination device or conversion LED. The primary radiation is here optionally in the visible, blue region of the electromagnetic spectrum, such as between 400 and 460 nm. Overlap of the primary and secondary radiation results in a white overall radiation or mixed radiation.

[0095] FIG. 2 shows a plot of a normalized Kubelka-Munk function (K/S) against the wavelength A in nm for Ca.sub.3Li.sub.4Si.sub.3O.sub.8N.sub.2:Eu.sup.2+ (WE1). K/S was calculated for this as follows:

K/S=(1−R.sub.inf).sup.2/2R.sub.inf, wherein R.sub.inf corresponds to the diffuse reflection (remission) of the phosphor.

[0096] From FIG. 2 it can be seen that the K/S maximum for Ca.sub.3Li.sub.4Si.sub.3O.sub.8N.sub.2:Eu.sup.2+ (WE1) is at about 300 nm. High K/S values mean high absorbance in this range. The phosphor can be efficiently excited with primary radiation from around 300 nm to 470 nm.

[0097] FIGS. 3a and 3b show the linking of Si(O,N).sub.4 tetrahedra in the crystal structure (orthorhombic, space group Pbcn) of Ca.sub.3Li.sub.4Si.sub.3O.sub.8N.sub.2:Eu.sup.2+ along the b axis of a unit cell within the crystal structure (FIG. 3a) and along the c axis of a unit cell within the crystal structure (FIG. 3b). Si(1) atoms (see Table 3) form SiO.sub.2N.sub.2 tetrahedra that are linked at their corners via N atoms of the SiO.sub.2N.sub.2 tetrahedra, forming zigzag chains along the b axis. Si(2) atoms (see Table 3) form SiO.sub.4 tetrahedra that are present in isolation, i.e. are not linked to any other tetrahedra. Oxygen and/or nitrogen atoms form the corners of the Si(O,N).sub.4 tetrahedra, with the Si atoms positioned in the centers of the tetrahedra.

[0098] FIGS. 3c and 3d show the linking of Li(O,N).sub.4 tetrahedra in the crystal structure (orthorhombic, space group Pbcn) of Ca.sub.3Li.sub.4Si.sub.3O.sub.8N.sub.2:Eu.sup.2+ along the b axis of a unit cell (FIG. 3c) and along the a axis of a unit cell (FIG. 3d). Li(1) atoms (see Table 3) form LiO.sub.3N tetrahedra and Li(2) atoms form LiO.sub.4 tetrahedra. The LiO.sub.3N and LiO.sub.4 tetrahedra are positioned alternately and linked to one another at their corners via oxygen atoms, forming layers of six-membered rings in the bc plane (FIG. 3d). Each tetrahedron is here part of three six-membered rings. Oxygen and/or nitrogen atoms form the corners of the Li(O,N).sub.4 tetrahedra, with the Li atoms positioned in the centers of the tetrahedra.

[0099] FIG. 3e shows the linking of the Si(O,N).sub.4 and Li(O,N).sub.4 tetrahedra shown in FIGS. 3a, 3b, 3c, and 3d. The section of the crystal structure is shown along the b axis. The Ca atoms occupy two different channels formed by Si(O,N).sub.4 and Li(O,N).sub.4 tetrahedra. Ca(1) atoms (see Table 3) are surrounded by six oxygen atoms in a distorted octahedral arrangement and Ca(2) atoms (see Table 3) are surrounded by six oxygen atoms and two nitrogen atoms in the form of a distorted square antiprism.

[0100] FIG. 3f shows the coordination sphere of Ca(1) atoms (see Table 3) in the crystal structure of Ca.sub.3Li.sub.4Si.sub.3O.sub.8N.sub.2:Eu.sup.2+. A Ca (1) atom is here surrounded by six oxygen atoms in a distorted octahedral arrangement.

[0101] FIG. 3g shows the coordination sphere of Ca(2) atoms (see Table 3) in the crystal structure of Ca.sub.3Li.sub.4Si.sub.3O.sub.8N.sub.2:Eu.sup.2+. A Ca (2) atom is here surrounded by six oxygen atoms and two nitrogen atoms in the form of a distorted square antiprism.

[0102] A crystallographic evaluation is given in FIG. 4. FIG. 4 shows a Rietveld refinement of the X-ray powder diffractogram of Ca.sub.3Li.sub.4Si.sub.3O.sub.8N.sub.2:Eu.sup.2+. The superposition of the measured reflections with the calculated reflections for Ca.sub.3Li.sub.4Si.sub.3O.sub.8N.sub.2:Eu.sup.2+ crystallizing in the orthorhombic space group Pbcn and the differences between the measured and calculated reflections are shown.

[0103] FIG. 5 shows a comparison of the emission spectrum of Ca.sub.3Li.sub.4Si.sub.3O.sub.8N.sub.2:Eu.sup.2+ (WE1) on excitation with primary radiation having a peak wavelength of 400 nm and of Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+ (CE1) on excitation with primary radiation having a peak wavelength of 460 nm. The optical data based on these emission spectra are shown in Table 5 below.

TABLE-US-00006 TABLE 5 Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+ Ca.sub.3Li.sub.4Si.sub.3O.sub.8N.sub.2:Eu.sup.2+ (CE1) (WE1) λ.sub.dom/nm 558 557 FWHM/nm 108 94 Luminous efficacy 449 458 (LER) Φ.sub.v/Φ.sub.e/lmW.sup.−1 LER relative to 100% 102% LU.sub.3Al.sub.5O.sub.12:Ce.sup.3+

[0104] As can be seen from Table 5, Ca.sub.3Li.sub.4Si.sub.3O.sub.8N.sub.2:Eu.sup.2+ (WE1) has a significantly smaller full width at half maximum than Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+ (CE1). The smaller full width at half maximum means that the luminous efficacy of the phosphor is also much higher and increased by 2% compared to the luminous efficacy of Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+ (CE1).

[0105] The inventors have thus succeeded in providing not only an alternative, but also a yellow-emitting phosphor that can be produced more efficiently and more inexpensively than garnet phosphors and is also very stable.

[0106] FIGS. 6 to 8 each show schematic side views of different embodiments of the illumination devices described here, in particular conversion LEDs.

[0107] The conversion LEDs in FIGS. 6 to 8 include at least one phosphor. In addition, one further phosphor or a combination of phosphors may be present in the conversion LED. The additional phosphors are known to the those skilled in the art and are therefore not mentioned explicitly at this point.

[0108] The conversion LED depicted in FIG. 6 has a semiconductor layer sequence 2 disposed atop a substrate 10. The substrate 10 may, for example, be designed to be in reflective form. Disposed atop the semiconductor layer sequence 2 is a conversion element 3 in the form of a layer. The semiconductor layer sequence 2 has an active layer (not shown) which, when the conversion LED is in operation, emits primary radiation having a wavelength 300 nm and 460 nm inclusive. The conversion element 3 is positioned in the beam path of the primary radiation S. The conversion element 3 comprises a matrix material, for example a silicone, epoxy resin or hybrid material, and particles of the phosphor 4, for example Ca.sub.3Li.sub.4Si.sub.3O.sub.8N.sub.2:Eu.sup.2+.

[0109] For example, the phosphor 4 has an average particle size of 10 μm. When the conversion LED is in operation, the phosphor 4 is capable of converting the primary radiation S at least partly or fully into secondary radiation SA in the yellow region of the spectrum. In the conversion element 3, the phosphor 4 is distributed homogeneously in the matrix material within the manufacturing tolerance.

[0110] Alternatively, the phosphor 4 may also be distributed in the matrix material with a concentration gradient.

[0111] Alternatively, the matrix material may also be absent, such that the phosphor 4 takes the form of a ceramic converter.

[0112] The conversion element 3 has been applied over the full area of the radiation exit face 2a of the semiconductor layer sequence 2 and of the side faces of the semiconductor layer sequence 2, and is in direct mechanical contact with the radiation exit face 2a of the semiconductor layer sequence 2 and the side faces of the semiconductor layer sequence 2. The primary radiation S may also exit via the side faces of the semiconductor layer sequence 2.

[0113] The conversion element 3 may be applied, for example, by injection molding, injection compression molding or spray coating methods. In addition, the conversion LED has electrical contacts (not shown here), the formation and disposition of which are known to those skilled in the art.

[0114] Alternatively, it is also possible for the conversion element to have been prefabricated and applied to the semiconductor layer sequence 2 by means of a “pick-and-place” process.

[0115] FIG. 7 shows a further working example of a conversion LED 1. The conversion LED 1 has a semiconductor layer sequence 2 atop a substrate 10. The conversion element 3 has been formed atop the semiconductor layer sequence 2. The conversion element 3 takes the form of platelets. The platelet may consist of particles of the inventive phosphor 4 that have been sintered together and hence be a ceramic platelet, or the platelet includes, for example, glass, silicone, an epoxy resin, a polysilazane, a polymethacrylate or a polycarbonate as matrix material with particles of the phosphor 4 embedded therein.

[0116] The conversion element 3 has been applied over the full area of the radiation exit face 2a of the semiconductor layer sequence 2. More particularly, no primary radiation S exits via the side faces of the semiconductor layer sequence 2; rather, it exits predominantly via the radiation exit face 2a. The conversion element 3 may have been applied atop the semiconductor layer sequence 2 by means of a bonding layer (not shown), composed for example of silicone.

[0117] The conversion LED 1 depicted in FIG. 8 has a housing 11 with a recess. A semiconductor layer sequence 2 having an active layer (not shown) is disposed within the recess. When the conversion LED is in operation, the active layer emits primary radiation S with a wavelength of 300 nm to 460 nm inclusive.

[0118] The conversion element 3 takes the form of an encapsulation of the layer sequence in the recess and comprises a matrix material, for example a silicone, and a phosphor 4, for example Ba.sub.3Li.sub.7Al.sub.3O.sub.11:Eu. When the conversion LED 1 is in operation, the phosphor 4 converts the primary radiation S at least partly into secondary radiation SA. Alternatively, the phosphor converts the primary radiation S fully into secondary radiation SA.

[0119] It is also possible that the phosphor 4 in the working examples in FIGS. 6 to 8 is arranged in the conversion element 3 spaced apart from the semiconductor layer sequence 2 or the radiation exit face 2a. This may be achieved for example by sedimentation or by applying the conversion layer atop the housing.

[0120] For example, by contrast with the embodiment depicted in FIG. 8, the encapsulation may consist solely of a matrix material, for example silicone, with application, atop the encapsulation, spaced apart from the semiconductor layer sequence 2, of the conversion element 3 as a layer atop the housing 11 and atop the encapsulation.

[0121] The working examples and features thereof that have been described in conjunction with the figures may in further working examples also be combined with one another, even when such combinations are not shown explicitly in the figures. In addition, the working examples described in conjunction with the figures may have additional or alternative features in accordance with the description in the general part.

[0122] This patent application claims the priority of German patent application 10 2018 004 827.7, the disclosure content of which is hereby incorporated by reference.

LIST OF REFERENCE SYMBOLS

[0123] 1 Illumination device or conversion LED [0124] 2 Semiconductor layer sequence or semiconductor chip [0125] 2a Radiation exit face [0126] 3 Conversion element [0127] 4 Phosphor [0128] 10 Substrate [0129] 11 Housing [0130] S Primary radiation [0131] SA Secondary radiation [0132] LED Light-emitting diode [0133] LER Luminous efficacy [0134] FWHM Full width at half maximum [0135] λ.sub.dom Dominant wavelength [0136] λ.sub.peak Peak wavelength [0137] λ.sub.prim Peak wavelength of the primary radiation [0138] ppm Parts per million [0139] WE Working example [0140] CE Comparative example [0141] g Gram [0142] I Intensity [0143] mol % Mole percent [0144] nm Nanometer [0145] ° C. Degree Celsius [0146] CIE-x, CIE-y Color coordinates in the CIE color space (1931)