NARROW-BAND GREEN LUMINOPHORE

Abstract

A luminophore may have the general molecular formula Na.sub.vK.sub.xRb.sub.yLi.sub.zCs.sub.w (Li.sub.3SiO.sub.4)4:E, where: v+x+y+z+w = 4; 0 < v < 4; 0 < x < 4; 0 < y < 4; 0 < z < 4; 0 < w < 4; and E = Eu, Ce, Yb, Mn, or combinations thereof.

Claims

1. A phosphor having the general molecular formula Na.sub.vK.sub.xRb.sub.yLi.sub.zCs.sub.w(Li.sub.3SiO.sub.4).sub.4:E, wherein: v+x+y+z+w = 4; 0 < v < 4; 0 < x < 4; 0 < y < 4; 0 < z < 4; 0 < w < 4; and E = Eu, Ce, Yb, Mn, or combinations thereof.

2. The phosphor as claimed in claim 1, wherein: 0 < v≤ 3; 0 < x ≤ 3; 0 < y ≤ 3; 0 < z ≤ 3; and 0 < w ≤ 3.

3. The phosphor as claimed in claim 1, wherein: 0 < v ≤ 2; - 0 < y ≤ 2; 0 < z ≤ 2; and 0 < w ≤ 2.

4. The phosphor as claimed in claim 1 , wherein: 0.05 ≤ v ≤ 1.50; 0.05 ≤ x ≤ 1.50; 0.05 ≤ y ≤ 1.50; 0.05 ≤ z ≤ 1.50; and 0.05 ≤ w ≤ 1.50.

5. The phosphor as claimed in claim 1 , wherein: 0.50 ≤ v ≤ 1.50; 0.50 ≤ x ≤ 1.50; 0.50 ≤ y ≤ 1.50; 0.50 ≤ z ≤ 1.50; and 0.05 ≤ w ≤ 0.5.

6. The phosphor as claimed in claim 1, wherein: 1.00 ≤ v ≤ 1.40; 0.80 ≤ x ≤ 1.20; 0.80 ≤ y ≤ 1.20; 0.60 ≤ z ≤ 1.00; and 0.05 ≤ w ≤ 0.30.

7. The phosphor as claimed in claim 1 , wherein: 1.08 ≤ v ≤ 1.28; 0.86 ≤ x ≤ 1.06; 0.82 ≤ y ≤ 1.02; 0.72 ≤ z ≤ 0.92; and 0.05 ≤ w ≤ 0.22.

8. The phosphor as claimed in claim 1 , wherein: 1.16 ≤ v ≤ 1.20; 0.94 ≤ x ≤ 0.98; 0.90 ≤ x ≤ 0.94; 0.80 ≤ z ≤ 0.84, and 0.10 ≤ w ≤ 0.14.

9. The phosphor as claimed in claim 1, wherein the crystal structure of which is tetragonal.

10. The phosphor as claimed in claim 9, wherein the phosphor crystallizes in the space group I4/m.

11. The phosphor as claimed in claim 1, wherein the phosphor has a peak wavelength ranging from 529 nm to 539 nm inclusive.

12. The phosphor as claimed in claim 1, wherein the phosphor has a full-width at half maximum ranging from 40 nm to 45 nm.

13. A lighting device comprising the phosphor as claimed in claim 1.

14. The lighting device as claimed in claim 13, further comprising: a semiconductor layer sequence configured to emit primary electromagnetic radiation; and a conversion element comprising the phosphor; and wherein the conversion element at least partially converts the primary electromagnetic radiation into secondary electromagnetic radiation .

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0117] Further advantageous embodiments and developments may be found in the exemplary embodiments described below in connection with the figures.

[0118] FIG. 1 shows a detail of the crystal structure of an exemplary embodiment of the phosphor.

[0119] FIG. 2 shows a Rietveld refinement of the X-ray diffraction powder diffractogram of an exemplary embodiment of the phosphor.

[0120] FIG. 3 shows an emission spectrum of an exemplary embodiment of the phosphor.

[0121] FIG. 4 shows the Kubelka-Munk function of an exemplary embodiment of the phosphor.

[0122] FIG. 5 shows an emission spectrum of two comparative examples.

[0123] FIG. 6 shows the thermal quenching behavior of an exemplary embodiment of the phosphor.

[0124] FIGS. 7 to 9 show schematic sectional representations of lighting devices.

[0125] FIG. 10 shows an emission spectrum of a comparative example.

DETAILED DESCRIPTION

[0126] FIG. 1 shows the tetragonal crystal structure of the phosphor having the molecular formula Na.sub.1.18K.sub.0.96Rb.sub.0.92Li.sub.0.82Cs.sub.0.12 (Li.sub.3SiO.sub.4) .sub.4:Eu.sup.2+. The filled circles represent Rb atoms (88.3%) and Cs atoms (11.7%), the unfilled circles represent Rb atoms (4.1%) and K atoms (95.9%), the unfilled circles with lines represent Li atoms (33.0%), and the filled circles with lines represent Li atoms (7.8%) and Na atoms (59.2%). The diagonally hatched polyhedra represented larger are LiO.sub.4 tetrahedra and the checkered polyhedra represented smaller are SiO.sub.4 tetrahedra. The (Li.sub.3SiO.sub.4) structural units comprise SiO.sub.4 and LiO.sub.4 tetrahedra, oxygen occupying the vertices and Li or Si respectively occupying the center of the tetrahedra. The (Li.sub.3SiO.sub.4) structural units form an (Li.sub.3SiO.sub.4) substructure which corresponds to the (Li.sub.3SiO.sub.4) substructure of known lithosilicates (J. Hofmann, R. Brandes, R. Hoppe, Neue Silicate mit “Stuffed Pyrgoms” [New silicates with Stuffed Pyrgoms]: CsKNaLi.sub.9 {Li[SiO.sub.4]} .sub.4, CsKNa.sub.2Li.sub.8{ Li[SiO.sub.4]} .sub.4, RbNa.sub.3Li.sub.8{Li[SiO.sub.4]} .sub.4, and RbNaLi.sub.4{Li[SiO.sub.4]} .sub.4, Z. Anorg. Allg. Chem., 1994, 620, 1495 -1508.), but the phosphor differs from known lithosilicates by the different occupancy of the two types of channels. The (Li.sub.3SiO.sub.4) substructure forms two types of channels along the crystallographic c axis. The first type of channels is occupied by the heavier alkali metals Cs, Rb and K. In this case, K and Rb are arranged alternately, Rb being partially substituted with Cs (11.7%) and K being partially substituted with Rb (4.1%) . The second type of channels is occupied by the lighter alkali metals Na and Li. In the second type of channels, not all Na and Li positions are fully occupied, the Na position being occupied by Na to 59.2% and Li to 7.8%, and the Li position being occupied to 33% by Li. The sum of the occupancy of the second type of channels was set to 100% in the refinement, in order to ensure charge neutrality. This new type of crystal structure of Na.sub.1.18K.sub.0.96Rb.sub.0.92Li.sub.0.82Cs.sub.0.12 (Li.sub.3SiO.sub.4).sub.4:Eu.sup.2+ is not previously known. The crystal structure is isostructural with the crystal structure of CsNaKLi (Li.sub.3SiO.sub.4) .sub.4 and CsNaRbLi (Li.sub.3SiO.sub.4) .sub.4 (J. Hofmann, R. Brandes, R. Hoppe, Neue Silicate mit “Stuffed Pyrgoms” [New silicates with Stuffed Pyrgoms] : CsKNaLi.sub.9{Li[SiO.sub.4]}.sub.4, CsKNa.sub.2Li.sub.8 {Li [SiO.sub.4]} .sub.4, RbNa.sub.3Li.sub.8 {Li[SiO.sub.4]} .sub.4, and RbNaLi.sub.4 {Li [SiO.sub.4]}.sub.4, Z. Anorg. Allg. Chem., 1994, 620, 1495 - 1508.). As described, Li in the crystal structure occupies on the one hand positions within the (Li.sub.3SiO.sub.4).sup.- substructure and on the other hand within the channels formed by the (Li.sub.3SiO.sub.4)- substructure, for which reason a nomenclature of the molecular formula may be Na.sub.1.18K.sub.0.96Rb.sub.0.92Li.sub.0.82CS.sub.0.12 (Li.sub.3SiO.sub.4).sub.4:Eu.sup.2+, Na.sub.1.18K.sub.0.96Rb.sub.0.92Cs.sub.0.12Li.sub.12.82Si.sub.4O.sub.16:Eu.sup.2+ also being usable. The phosphor crystallizes in the space group I4/m. The crystal structure was determined by means of single-crystal (details in Tables 2, 3 and 4 below) and powder X-ray diffraction experiments (FIG. 2).

[0127] The crystallographic data of Na.sub.1.18K.sub.0.96Rb.sub.0.92Li.sub.0.82Cs.sub.0.12 (Li.sub.3SiO.sub.4).sub.4:Eu.sup.2+ are shown in Table 2.

TABLE-US-00002 Molecular formula CS.sub.0.12Rb.sub.0.92K.sub.0.96Na.sub.1.18Li.sub.0.82 (Li.sub.3SiO.sub.4) .sub.4:Eu Molar mass / g×mol.sup.-1 308.30 (without Eu) Crystal system Tetragonal Space group I4/m (no 87) a / Å 11.0063(5) b / Å 11.0063(5) c / Å 6.3336 (3) Cell volume / Å.sup.3 767.24 (8) Density / g×cm.sup.-3 2.669 T / K 296 Radiation Cu-Kα (λ = 1.542 Å) Measurement range 5.7 < θ < 74.3 -13 ≤ h ≤ 13 -13 ≤ k ≤ 13 -7 ≤ 1 ≤ 7 Total reflections 3550 Independent reflections 423 Number of parameters 32 R.sub.int, Rσ 0.0346, 0.0222 Δρmax, Δρmin / eÅ.sup.-3 0.42/-0.44 R.sub.1 (obs/all) 0.026/0.027 wR2 (obs/all) 0.066/0.066 GooF (obs/all) 1.14/1.14

[0128] The atom layers of Na.sub.1.18K.sub.0.96Rb.sub.0.92Li.sub.0.82Cs.sub.0.12 (Li.sub.3SiO.sub.4) .sub.4 :Eu.sup.2+ are shown in Table 3.

TABLE-US-00003 Atom x y z Occupanc y Uiso Rb01 ½ ½ 0 0.883 (11 ) 0.0176 (3) Cs01 ½ ½ 0 0.117 (11 ) 0.0176 (3) K002 ½ ½ ½ 0.959 (8) 0.0120(6) Rb02 ½ ½ ½ 0.041 (8) 0.0120(6) Si03 0.21585(8) 0.42217 (8) ½ 1 0.0060 (3) Na04 0 ½ ¾ 0.592 (13 ) 0.0113 (12 ) Li04 0 ½ ¾ 0.078 (13 ) 0.0113 (12 ) 0005 0.0996(2) 0.3307 (2) ½ 1 0.0106(5) 0006 0.29593 (15 ) 0.40548 (16 ) 0.2842 (3 ) 1 0.0110 (4) 0007 0.1631(2) 0.5621(2) ½ 1 0.0093(5) Li08 0.0749(6) 0.7118(6) ½ 1 0.0124 (13 ) Li09 0.3857(4) 0.2575(5) 0.2574 (7 ) 1 0.0173 (10 ) Li10 0 ½ ½ 0.33 (5) 0.022(11)

[0129] The anisotropic displacement parameters of Na.sub.1.18K.sub.0.96Rb.sub.0.92Li.sub.0.82Cs.sub.0.12 (Li.sub.3SiO.sub.4) .sub.4: Eu.sup.2+ are shown in Table 4.

TABLE-US-00004 Atom U.sub.11 U.sub.22 U.sub.33 U.sub.27 U.sub.13 U.sub.1.sub.2 Rb01 0.0199 (3) 0.0199 (3) 0.0131 (4) 0 0 0 Ca01 0.0199 (3) 0.0199 (3) 0.0131 (4) 0 0 0 K002 0.0107 (6) 0.0107 (6) 0.0146 (9) 0 0 0 Rb02 0.0107 ( 6 ) 0.0107 (6) 0.0146 (9) 0 0 0 Na04 0.0109(13) 0.0109 (13) 0.012(2) 0 0 0 L104 0.0109 (13) 0.0109 (13) 0.012 (2) 0 0 0

[0130] FIG. 2 shows a Rietveld refinement of the X-ray diffraction powder diffractogram of Na.sub.1.18K.sub.0.96Rb.sub.0.92Li.sub.0.82Cs.sub.0.12(Li.sub.3SiO.sub.4) .sub.4:Eu. With the aid of the measured X-ray powder diffractogram, the high purity of the phosphor may be seen. The superposition of the measured reflections with the calculated reflections is in this case represented in the upper diagram. The differences between the measured and calculated reflections are represented in the lower diagram.

[0131] FIG. 3 shows the emission spectrum of Na.sub.1.18K.sub.0.96Rb.sub.0.92Li.sub.0.82Cs.sub.0.12 (Li.sub.3SiO.sub.4).sub.4:Eu.sup.2+. The wavelength is plotted in nanometers on the x axis and the relative intensity in percent is plotted on the y axis. In order to measure the emission spectrum, a powder of the phosphor was excited with primary radiation having a wavelength of 400 nm. The phosphor has a peak wavelength of 534 nm and a dominant wavelength of 543 nm. The full-width at half maximum is 42.3 nm and the color point in the CIE color space is at the coordinates CIE-x: 0.259 and CIE-y: 0.697. As may be seen, the emission spectrum of the phosphor exhibits only one emission peak. The peak wavelength therefore represents not only the absolute maximum but also the only maximum within the emission spectrum.

[0132] In response to excitation of a powder of the phosphor with primary radiation having a wavelength of 460 nm (not shown), the phosphor exhibits a peak wavelength of 534 nm and a dominant wavelength of 542.7 nm. The full-width at half maximum is 43.5 nm and the color point in the CIE color space has the coordinates CIE-x: 0.257 and CIE-y: 0.702. Here again, the emission spectrum of the phosphor has only one emission peak and the peak wavelength represents the absolute and only maximum.

[0133] In contrast, the emission spectrum shown in FIG. 10 of the phosphor Cs.sub.4-x-y-zRb.sub.xNa.sub.yLi.sub.z [Li.sub.3SiO.sub.4].sub.4:Eu has two emission peaks and therefore undesired double emission.

[0134] The emission of the phosphor exhibits a large overlap with the transmission range of a standard green filter, so that only little light is lost and the achievable color space is large. The phosphor Na.sub.1.18K.sub.0.96Rb.sub.0.92Li.sub.0.82Cs.sub.0.12 (Li.sub.3SiO.sub.4).sub.4:Eu.sup.2+ is therefore suitable in particular for conversion LEDs for backlighting applications for displays.

[0135] FIG. 4 shows a normalized Kubelka-Munk function (KMF), plotted against the wavelength λ in nm, for Na.sub.1.18K.sub.0.96Rb.sub.0.92Li.sub.0.82Cs.sub.0.12 (Li.sub.3SiO.sub.4).sub.4:Eu.sup.2+. The KMF was in this case calculated as follows:

[0136] KMF = R.sub.inf).sup.2/2R.sub.inf, where R.sub.inf corresponds to the diffuse reflection (remission) of the phosphor.

[0137] It may be seen from FIG. 4 that the phosphor can be excited efficiently with primary radiation between 330 nm and 500 nm. High KMF values mean a high absorption in this range.

[0138] FIG. 5 shows the emission spectra of the known phosphors Lu.sub.3(Al,Ga).sub.5O.sub.12:Ce (G2) and (Sr,Ba).sub.2SiO.sub.4:Eu (OS2).

[0139] Table 5 shows a comparison of the spectral data of the phosphor Na.sub.1.18K.sub.0.96Rb.sub.0.92Li.sub.0.82Cs.sub.0.12 (Li.sub.3SiO.sub.4).sub.4:Eu.sup.2+ (AB) with the known phosphors Lu.sub.3(Al,Ga).sub.5O.sub.12:Ce (G2) and (Sr,Ba).sub.2SiO.sub.4:Eu (OS2).

TABLE-US-00005 AB G2 OS2 CIE-x 0.259 0.287 0.263 CIE-y 0.697 0.536 0.645 λ.sub.peak / nm 534.0 537.4 536.3 λ.sub.dom / nm 543.0 541.3 541.5 FWHM / nm 42.3 102.0 65.3 LER / lm.Math. W.sub.opt.sup.-1 570.9 418.6 490.8 Color purity / % 90.2 49.0 75.3

[0140] All three phosphors exhibit a similar dominant wavelength. The phosphor AB, however, exhibits a much higher luminous efficiency (LER) and a significantly higher color purity. This leads to a better color purity and to a better overall efficiency.

[0141] The thermal quenching behavior of the phosphor Na.sub.1.18K.sub.0.96Rb.sub.0.92Li.sub.0.82Cs.sub.0.12 (Li.sub.3SiO.sub.4).sub.4:Eu.sup.2+ is represented in FIG. 6. The phosphor was excited with primary radiation having a wavelength of 400 nm at various temperatures from 25 to 225° C., during which its emission intensity was recorded. The phosphor exhibits only a small loss of emission intensity at typical temperatures which prevail in a conversion LED, in particular temperatures above 140° C. Even at 200° C., the loss is only 10%. The thermal quenching behavior is therefore even better than that of L.sub.u3Al.sub.5O.sub.12:Ce. The phosphor may therefore advantageously be used even at relatively high operating temperatures in conversion LEDs.

[0142] FIGS. 7 to 9 respectively show schematic side views of various embodiments of lighting devices as described here, in particular conversion LEDs.

[0143] The conversion LEDs of FIGS. 7 to 9 comprise at least one phosphor as described here. In addition, there may be a further phosphor or a combination of phosphors in the conversion LED. The additional phosphors are known to the person skilled in the art and will therefore not be explicitly mentioned at this point.

[0144] The conversion LED according to FIG. 7 comprises a semiconductor layer sequence 2, which is arranged on a substrate 10. The substrate 10 may, for example, be configured to be reflective. A conversion element 3 in the form of a layer is arranged over the semiconductor layer sequence 2. The semiconductor layer sequence 2 comprises an active layer (not shown), which emits primary radiation with a wavelength of from 340 nm to 460 nm during operation of the conversion LED. The conversion element 3 is arranged 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.

[0145] The phosphor 4 is capable of converting the primary radiation S during operation of the conversion LED at least partially or fully into secondary radiation SA in the green spectral range, in particular with a peak wavelength of between 529 nm and 539 nm inclusive. In the conversion element 3, the phosphor 4 is distributed homogeneously in the matrix material within the scope of manufacturing tolerance.

[0146] Alternatively, the phosphor 4 may also be distributed with a concentration gradient in the matrix material.

[0147] Alternatively, the matrix material may also be omitted, so that the phosphor 4 is formed as a ceramic converter.

[0148] The conversion element 3 is applied fully over the radiation exit surface 2a of the semiconductor layer sequence 2 and over the side faces of the semiconductor layer sequence 2, and is in direct mechanical contact with the radiation exit surface 2a of the semiconductor layer sequence 2 and the side faces of the semiconductor layer sequence 2. The primary radiation S may also emerge through the side faces of the semiconductor layer sequence 2.

[0149] The conversion element 3 may for example be applied by injection-molding, transfer-molding or spray-coating methods. Furthermore, the conversion LED comprises electrical contacts (not shown here), the configuration and arrangement of which are known to the person skilled in the art.

[0150] Alternatively, the conversion element may also be prefabricated and applied onto the semiconductor layer sequence 2 by means of a so-called pick-and-place process.

[0151] A further exemplary embodiment of a conversion LED 1 is shown in FIG. 8. The conversion LED 1 comprises a semiconductor layer sequence 2 on a substrate 10. The conversion element 3 is formed on the semiconductor layer sequence 2. The conversion element 3 is formed as a platelet. The platelet may consist of particles of the phosphor 4 which are sintered together, and it may therefore be a ceramic platelet, or the platelet comprises 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.

[0152] The conversion element 3 is applied surface-wide over the radiation exit surface 2a of the semiconductor layer sequence 2. In particular, no primary radiation S emerges through the side faces of the semiconductor layer sequence 2, but instead it emerges predominantly through the radiation exit surface 2a. The conversion element 3 may be applied on the semiconductor layer sequence 2 by means of an adhesion layer (not shown), for example consisting of silicone.

[0153] The conversion LED 1 according to FIG. 9 comprises a housing 11 with a recess. A semiconductor layer sequence 2, which comprises an active layer (not shown), is arranged in the recess. The active layer emits primary radiation S with a wavelength of from 340 nm to 460 nm during operation of the conversion LED.

[0154] The conversion element 3 is formed as an encapsulation of the layer sequence in the recess and comprises a matrix material, for example a silicone, and a phosphor 4, for example Na.sub.1.18K.sub.0.96Rb.sub.0.92Li.sub.0.82Cs.sub.0.12 (Li.sub.3SiO.sub.4).sub.4:Eu. The phosphor 4 converts the primary radiation S at least partially into secondary radiation SA during operation of the conversion LED 1. Alternatively, the phosphor converts the primary radiation S fully into secondary radiation SA.

[0155] In the exemplary embodiments of FIGS. 7 to 9, it is also possible for the phosphor 4 to be arranged spatially separated from the semiconductor layer sequence 2 or the radiation exit surface 2a in the conversion element 3. This may, for example, be achieved by sedimentation or by application of the conversion layer on the housing.

[0156] For example, in contrast to the embodiment of FIG. 9, the encapsulation may consist only of a matrix material, for example silicone, the conversion element 3 being applied on the encapsulation at a distance from the semiconductor layer sequence 2 as a layer on the housing 11 and on the encapsulation.

[0157] The exemplary embodiments described in connection with the figures, and the features thereof, may also be combined with one another according to further exemplary embodiments, even if such combinations are not explicitly shown in the figures. Furthermore, the exemplary embodiments described in connection with the figures may comprise additional or alternative features according to the description in the general part.

LIST OF REFERENCES

[0158] 1 lighting device or conversion LED [0159] 2 semiconductor layer sequence or semiconductor chip [0160] 2a radiation exit surface [0161] 3 conversion element [0162] 4 phosphor [0163] 10 substrate [0164] 11 housing [0165] S primary radiation [0166] SA secondary radiation [0167] LED light-emitting diode [0168] LER luminous efficiency [0169] W watt [0170] lm lumen [0171] λ.sub.dom dominant wavelength [0172] ppm parts per million [0173] AB exemplary embodiment [0174] g gram [0175] IR relative intensity [0176] mol% molar percent [0177] KMS Kubelka-Munk function [0178] K kelvin [0179] cm centimeter [0180] nm nanometer [0181] °2θ degrees 2 Theta [0182] T temperature [0183] °C degrees Celsius