Abstract
The invention relates to a red-emitting luminescent material of the formula AE16xCexSi17zAlzN32+yzO2y+z wherein AE=Mg, Ca, Sr and/or Ba, 0<x2, 0y<5, 0z3 and y+z<2.
Claims
1. Phosphor of the formula AE.sub.16xCe.sub.xSi.sub.17-zAl.sub.zN.sub.32+yzO.sub.2y+z with AE=Mg, Ca, Sr and/or Ba, 0<x2, 0y<5, 0z3 and y+z<8, wherein the phosphor has a cubic crystal system with the space group F 4 3m.
2. Phosphor according to claim 1, wherein the lattice constant a is at a=14.715.1 .
3. Phosphor according to claim 1, wherein 0.0016<x1.6.
4. Phosphor according to claim 1, wherein z=0 and y=x.
5. Phosphor according to claim 1, which is configured to emit radiation in the red spectral range of the electromagnetic spectrum.
6. Phosphor according to claim 1, which has an emission maximum in the range from 630 nm to 680 nm.
7. Method for producing a phosphor of the formula AE.sub.16xCe.sub.xSi.sub.17-zA1.sub.zN.sub.32+yzO.sub.2y+z, with AE=Mg, Ca, Sr and/or Ba, 0<x2, 0y<5, 0z3 and y+z<8, wherein the phosphor is configured to emit radiation in the red spectral range of the electromagnetic spectrum, comprising the method steps A) Mixing of the starting materials comprising an Mg, Ba, Sr and/or Ca nitride, Si.sub.3N.sub.4, CeO.sub.2, SiO.sub.2 and/or an Mg, Ba, Sr, Al and/or Ca oxide, wherein the proportion of oxygen in the starting materials is 2 mol % to 20 mol % in relation to the total quantity of nitrogen and oxygen in the starting materials, B) Heating of the mixture obtained in A) to a temperature over 1200 C., C) Annealing of the mixture at a temperature over 1200 C. for at least 4 hours, D) Cooling of the mixture to room temperature.
8. Method according to claim 7, wherein the method steps A) to D) are executed in a nitrogen atmosphere.
9. Method according to claim 7, wherein the starting materials in method step A) comprise AlN.
Description
(1) Further advantageous embodiments and developments of the invention result from the exemplary embodiments described below in connection with the figures.
(2) FIG. 1a shows the measured X-ray diffraction powder diffractogram of a phosphor described here,
(3) FIGS. 1b to 1d shows the data of the X-ray diffraction powder diffractogram shown in FIG. 1a,
(4) FIG. 2a shows a measured X-ray diffraction powder diffractogram of a phosphor described here, an X-ray diffraction powder diffractogram calculated according to the Rietveld method and their difference,
(5) FIGS. 2b to 2d show crystallographic data of a phosphor described here,
(6) FIG. 2e shows a schematic representation of the cubic crystal structure of a phosphor described here,
(7) FIG. 3a shows the emission spectrum of a phosphor described here,
(8) FIG. 3b shows the degree of reflection of a phosphor described here,
(9) FIG. 4 shows the dependence of the formation of a phosphor described here on the oxygen content of the starting materials.
(10) In FIG. 1a the X-ray diffraction powder diffractogram of the phosphor Ca.sub.15.84Ce.sub.0.16Si.sub.17N.sub.32.16O.sub.1.84 using copper K.sub.1 radiation is indicated. On the x-axis the diffraction angles are indicated in 2 values and on the y-axis the relative intensity (I.sub.r) is shown.
(11) The phosphorCa.sub.15.68Ce.sub.0.32Si.sub.17N.sub.32.32O.sub.1.68, which has the X-ray diffraction powder diffractogram shown in FIG. 1a, was produced as follows: 23.275 g Ca.sub.3N.sub.2, 28.236 g Si.sub.3N.sub.4, 1.039 g CeO.sub.2 and 7.45 g CaO are ground in powder form in a ball mill with the addition of ZrO.sub.2 balls in a glovebox (atmosphere: N2, [O]<1 ppm, [H2O]<1 ppm) for six hours. The mole ratio of Ca:Ce:Si:O of the starting materials is 17.03:0.16:17:4.09. O is present in the starting materials at 13 mol % in relation to the total quantity of N in the starting materials and at 12 mol % relative to the 34 lattice sites available for N and O in the crystal lattice. O is present in the starting materials at 12 mol % in relation to the total quantity of N and O in the starting materials. The homogeneous mixture is transferred to a tungsten crucible, which is transferred to a tube furnace. The mixture is heated in a nitrogen atmosphere at a heating rate of 250 C. per hour to a temperature of 1600 C. The mixture is annealed for 4 hours at a temperature of 1600 C., then cooling takes place to room temperature at a cooling rate of 250 C. per hour. The pink-colored product is ground in an Achat mortar grinder. Then the phosphor is characterized.
(12) In the table in FIGS. 1bto 1d , the data of the X-ray diffraction powder diffractogram shown in FIG. 1a is listed. d describes the lattice plane distance and hkl the Miller indices in the table.
(13) In FIG. 2a the diffraction angles are indicated in 2 values on the x-axis and the relative intensity (Ir) is plotted on the y-axis. The curve provided with the reference sign I shows a measured X-ray diffraction powder diffractogram and corresponds to that of the phosphorCa.sub.15.84Ce.sub.0.16Si.sub.17N.sub.32.16O.sub.1.84, the X-ray diffraction powder diffractogram of which is already shown in FIG. 1a. The X-ray diffraction powder diffractogram I that is obtained was analyzed by means of a Riedveld analysis. In a Riedveld method the crystal structure is varied until the diffractogram calculated from it best coincides with the measured diffractogram. The structure of Ca.sub.16Si.sub.17N.sub.34 was used as a basis for the Riedveld method. According to Hick et al., Inorganic Chemistry 2012, 51, 12626, Ca.sub.16Si.sub.17N.sub.34 has a cubic crystal structure with a lattice constant a=14.888 and belongs to the space group F 4 3m. The diagram provided with the reference sign II corresponds to the calculated X-ray diffraction powder diffractogram for the phosphor Ca.sub.15.84Ce.sub.0.16Si.sub.17N.sub.32.16O.sub.1.84. The diagram provided with the reference sign III shows the difference between the X-ray diffraction powder diffractogram with the reference sign I and the calculated diagram with the reference sign II. As is apparent, the correspondence between the measured X-ray diffraction powder diffractogram with the reference sign I and the calculated diagram with the reference sign II is very high.
(14) The data of the Rietveld refinement and the most important crystallographic data of the phosphor Ca.sub.15.84Ce.sub.0.16Si.sub.17N.sub.32.16O.sub.1.84 are shown in the tables in FIGS. 2b to 2d.
(15) FIG. 2e shows the cubic crystal structure of the phosphor Ca.sub.15.84Ce.sub.0.16Si.sub.17N.sub.32.16O.sub.1.84 in a schematic representation. The phosphor crystallizes cubically in the space group F 4 3m. The structure of the phosphor was determined with reference to the X-ray diffraction powder diffractogram by the Rietveld analysis. A unit cell consists of eight clusters, which are each constructed of eight edge-linked SiN.sub.4 tetrahedra. The sites of the N in the tetrahedra are partly replaced by O. In FIG. 3a, four of these clusters are shown. Four of the clusters are freestanding, the other four clusters are linked via corner linking to central SiN.sub.4 tetrahedra on the centers of the surface of the unit cell to a three-dimensional space network.
(16) In FIG. 3a the emission spectrum of the phosphor Ca.sub.15.68Ce.sub.0.32Si.sub.17N.sub.32.32O.sub.1.68 is depicted. The wavelength in nanometers is plotted on the x-axis and the emission intensity in percent on the y-axis. The phosphor has a full width at half maximum of about 120 nm and a dominant wavelength of over 590 nm, the maximum of the emission is at approximately 650 nm.
(17) FIG. 3b shows the degree of reflection of the phosphor Ca.sub.15.68Ce.sub.0.32Si.sub.17N.sub.32.32O.sub.1.68 as a function of the wavelength. The wavelength in nanometers is plotted on the x-axis and the degree of reflection in percent on the y-axis. As is evident, the phosphor according to the invention can be excited with a wavelength of between 350 and 550 nm, since the reflection here is relatively low and the absorption is particularly high.
(18) FIG. 4 shows the dependence of the formation of the phosphor of the general formula Ca.sub.16xCe.sub.xSi.sub.17N.sub.32+xO.sub.2-x with x=0.16 in cubic crystal structure in the space group F 4 3m as a function of the oxygen content of the starting materials. Plotted on the x-axis is the oxygen content (c(O)) of the starting materials CeO.sub.2 and CaO in mole percent in relation to the total quantity of nitrogen and oxygen in the starting materials and on the y-axis the proportion of the phosphor Ca.sub.16xCe.sub.xSi.sub.17N.sub.32+xO.sub.2, arising with x=0.16 in cubic crystal structure in the space group F 4 3m (c(L)) in percent. As is evident, the phosphor is formed 100% or nearly 100% if oxygen at 12 mol % in relation to the total quantity of nitrogen and oxygen is weighed out in the starting materials. If the proportion of oxygen is 1%, the phosphor does not form. In the range between 0% and about 12%, orthorhombic phases of CaSiN.sub.2:Ce form in addition to the target phase. Thus it is shown that the presence of oxygen in the starting materials is essential for the formation of the phosphor with the general formula AE.sub.16xCe.sub.xSi.sub.17zAl.sub.zN.sub.32+yzO.sub.2y+z with AE=Mg, Ca, Sr and/or Ba, 0<x2, 0y<5, 0z3 and y+z<2.
(19) The invention is not restricted by the description with reference to the exemplary embodiments to these. On the contrary, the invention comprises every new feature as well as every combination of features, which includes in particular every combination of features in the Claims, even if this feature or this combination is not itself explicitly specified in the Claims or exemplary embodiments.
REFERENCE SIGN LIST
(20) Ir Relative intensity d Lattice plane distance hkl Miller indices I, II, X-ray diffraction powder diffractogram III Difference between X-ray diffraction powder diffractogram I and II Wavelength nm Nanometer E Emission intensity R Degree of reflection c(O) Oxygen content c(L) Proportion of phosphor arising
