are mixed, calcined and cooled in a molar ratio of 1:1 to prepare ALiSiF₆and in a second step ALiSiF₆is milled in a ball mill with X′₂MnF₆to prepare ALiSiF₆:Mn.

In at least one embodiment, a molar ratio of the molar amount of ALiSiF₆to the molar amount of X′₂MnF₆is between 1.000 to 0.200 and 1.000 to 0.001, for example 1 to 0.043.

In at least one embodiment, a molar ratio of the molar amount of KLiSiF₆to the molar 5 amount of K₂MnF₆is between 1.000 to 0.200 and 1.000 to 0.001, for example 1 to 0.043.

A conversion LED may include the luminophore. All details and definitions relating to the luminophore and to the process for preparing the luminophore are also applicable to the conversion LED, and vice versa.

In at least one embodiment, the conversion LED comprises a semiconductor layer sequence. The semiconductor layer sequence is adapted to emit electromagnetic primary radiation.

In at least one embodiment, the semiconductor layer sequence comprises at least one III-V compound semiconductor material. The semiconductor material is, for example, a nitride compound semiconductor material, such as Al_nIn_1-n-mGa_mN where, in each case, 0≤n≤1, 0≤m≤1 and n+m≤1. The semiconductor layer sequence may comprise dopants and additional constituents. For the sake of simplicity, however, only the essential constituents of the semiconductor layer sequence, i.e. Al, Ga, In and N, are specified, even though these may be replaced and/or supplemented to some degree by small amounts of further substances. The semiconductor layer sequence is especially formed from InGaN.

The semiconductor layer sequence comprises an active layer having at least one pn junction and/or having one or more quantum well structures. In the operation of the conversion LED, electromagnetic radiation is produced in the active layer. A wavelength or the emission maximum of the radiation may be in the ultraviolet and/or visible region, especially at wavelengths between 300 nm and 470 nm inclusive.

The conversion LED may be adapted to emit white or colored light.

In combination with the luminophore present in the conversion LED, the conversion LED may be adapted to emit red light in full conversion or white light in partial or full conversion. Such conversion LEDs are especially suitable for applications where a high color rendering index (e.g. R9) is required, as in general lighting or background lighting, for example of displays suitable for representation of large color spaces.

The conversion LED comprises a conversion element. In particular, the conversion element comprises the luminophore or consists of the luminophore. The luminophore at least partly or fully converts the electromagnetic primary radiation to electromagnetic secondary radiation in the red spectral region.

In at least one embodiment, the conversion element or conversion LED comprises no further luminophore in addition to the luminophore. The conversion element may also consist of the luminophore. The luminophore may be adapted to fully convert the primary radiation. In this embodiment the overall radiation from the conversion LED is in the red region of the electromagnetic spectrum.

In at least one embodiment, the conversion element or conversion LED comprises a further red-emitting luminophore in addition to the luminophore. The conversion element may also consist of the luminophore and the further red-emitting luminophore. The luminophores may be adapted to fully convert the primary radiation. In this embodiment the overall radiation from the conversion LED is in the red region of the electromagnetic spectrum. For example, the further red-emitting luminophore may have the formula Sr[Al₂Li₂O₂N₂]:Eu. Sr[Al₂Li₂O₂N₂]:Eu may crystallize in the tetragonal P4₂/m space group. The further luminophore advantageously allows the color locus of the overall radiation to be adapted as required. This additionally makes it possible to achieve particularly high color saturation and efficiency that typically cannot be achieved by the use of just one luminophore.

In at least one embodiment, the conversion element comprises a second and/or third luminophore in addition to the luminophore. The conversion element may comprise further luminophores in addition to the luminophore, the second luminophore and the third luminophore. The luminophores are embedded in a matrix material for example. Alternatively, the luminophores may also be in a converter ceramic.

The conversion LED may comprise a second luminophore for emission of radiation from the green spectral region.

Alternatively or in addition, the conversion LED may comprise a third luminophore. The third luminophore may be adapted for emission of radiation from the yellow spectral region. In other words, the conversion LED may then comprise at least three luminophores: a yellow-emitting luminophore, a green-emitting luminophore and the red-emitting luminophore. The conversion LED is adapted for full conversion or partial conversion, where the primary radiation in the case of full conversion may be selected from the UV to blue spectral region and in the case of partial conversion from the blue region. The resulting overall radiation from the conversion LED is then especially white mixed radiation.

Alternatively or in addition, the conversion LED may comprise a fourth luminophore. The fourth luminophore may be adapted for emission of radiation from the blue spectral region. The conversion LED may then comprise at least three luminophores: a blue-emitting luminophore, a green-emitting luminophore and the red-emitting luminophore. The conversion LED may then comprise at least four luminophores: a blue-emitting luminophore, a green-emitting luminophore, a yellow-emitting luminophore and the red-emitting luminophore. The conversion LED is adapted for full conversion, where the primary radiation in the case of full conversion may be selected from the UV spectral region. The resulting overall radiation from the conversion LED is then especially white mixed radiation.

Yellow, blue and green luminophores are known to the person skilled in the art and are not detailed separately here.

Luminophores present in addition to the luminophore may especially increase the color rendering index. Further luminophores in addition to the second, third and/or fourth luminophore are especially not ruled out. The higher the color rendering index, the more true, or true to nature, the color impression perceived.

WORKING EXAMPLE

KLiSiF₆was prepared by means of solid-state synthesis in a multi-anvil high-pressure press at a pressure of 5.5 GPa (55 kbar) and high temperatures. The reactants employed were Li₂SiF₆and K₂SiF₆in a molar ratio of 1 to 1. The pressure of 55 kbar was built up over 145 minutes. The temperature was increased at a heating rate of 75° C. per minute to 750° C. and the temperature of 750° C. was maintained for 150 minutes. Thereafter, the temperature was cooled to 350° C. at a cooling rate of 2.22° C. per minute and the product KLiSiF₆was subsequently quenched to room temperature (25° C.). The pressure was subsequently relieved over 430 minutes.

The obtained KLiSiF₆was then milled in a ball mill with K₂MnF₆to effect doping of KLiSiF₆with Mn and prepare the inventive luminophore KLiSiF₆:Mn⁴⁺. This comprises milling the sample with the reagent K₂MnF₆for 10 minutes at 300 rpm six times. A pause of 15 minutes is maintained between the milling steps. Analysis by x-ray powder methods shows that the luminophore can be prepared in good quality (FIGS. 3A and 3B).

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantageous embodiments and developments are apparent from the working examples described hereinbelow with reference to the figures.

FIG. 1A shows the unit cell of cubic K₂SiF₆(space group no. 225; Fm-3m).

FIG. 1B shows the unit cell of cubic KLiSiF₆.

FIG. 2 shows an emission spectrum of the inventive luminophore KLiSiF₆:Mn⁴⁺.

FIG. 3A shows a PXRD comparison (Mo—Kα₁radiation) of KLiSiF₆with a simulation of KLiSiF₆based on single-crystal data.

FIG. 3B shows a PXRD comparison (Mo—Kα₁radiation) of KLiSiF₆:Mn⁴⁺ with KLiSiF₆.

FIG. 3C shows a comparison of PXRD simulations (Mo—Kα₁radiation) of KLiSiF₆and Li₂SiF₆based on single-crystal data.

FIG. 3D shows a comparison of PXRD simulations (Mo—Kα₁radiation) of KLiSiF₆and K₂SiF₆based on single-crystal data.

FIG. 4 shows an emission spectrum of the inventive luminophore KLiSiF₆:Mn⁴⁺ compared to K₂SiF₆:Mn⁴⁺.

FIG. 5 shows a luminous efficacy of radiation (LER) of KLiSiF₆:Mn⁴⁺ compared to K₂SiF₆:Mn⁴⁺.

DETAILED DESCRIPTION

FIG. 1A shows the unit cell of the crystal structure of K₂SiF₆, which crystallizes in the cubic space group Fm-3m. The K atoms are shown as unfilled circles, the F atoms as filled circles, and [SiF₆]²⁻ octahedra with Si in the center and F at the vertices with hatching. In the luminophore K₂SiF₆:Mn⁴⁺ Si has been partly replaced by Mn (not shown, no measurable effect on crystal structure). K₂SiF₆(with or without Mn⁴⁺) crystallizes in the K₂PtCl₆type in the space group Fm-3m (no. 225). The unit cell shows a cubic metric with a lattice parameter a=8.134(1) Å.

FIG. 1B shows the unit cell of the crystal structure of KLiSiF₆. The K atoms are shown as unfilled circles, the F atoms as filled circles, [SiF₆]²⁻ octahedra with Si in the center and F at the vertices with fine hatching and [LiF₆]⁵⁻ octahedra with Li in the center and F at the vertices with coarse hatching. In the luminophore KLiSiF₆:Mn⁴⁺ Si has been partly replaced by Mn (not shown, no measurable effect on crystal structure) and so Mn⁴⁺ is octahedrally surrounded by F atoms. Compared to K₂SiF₆(with or without Mn⁴⁺), KLiSiF₆(with or without Mn⁴⁺) surprisingly crystallizes in the space group Pbcn (no. 60) and the unit cell shows an orthorhombic metric with lattice parameters a=747.50(3) pm, b=1158.58(5) pm and c=979.77(4) pm. The crystal structure, the units and the bonding patterns thereof are similar to what is observed in (NH₄)MnFeF₆.

The crystallographic data are shown in table 1.

TABLE 1

Empirical formula
KLiSiF6

Crystal system
orthorhombic

Space group
Pbcn (no. 60)

a/pm
747.50(3)

b/pm
1158.58(5)

c/pm
979.77(4)

Cell volume/nm³
0.8485(1)

Z
8

Density/g × cm⁻³
2.945

T/K
203(2)

Diffractometer
BRUKER D8 Quest

Radiation/Å
Mo-Kα (λ = 0.71073)

Measured range/°
6.5 < 2θ < 75.8

−12 < h < 12

−19 < k < 19

−16 < l < 16

R₁/wR₂[I ≥ 2σ(I)]
0.0188/0.0420

R₁/wR₂[all data]
0.0255/0.0438

GooF
1.080

Comparison of the FIGS. 1A and 1B clearly shows that the crystal structures appreciably differ from one another. Cubic K₂SiF₆for example comprises only [SiF6]²⁻octahedra, which are spatially separate from one another, while KLiSiF₆comprises two different units, [SiF6]²⁻and [LiF6]⁵⁻octahedra, which are additionally bonded to one another. The same differences are thus also present in the crystal structures of K₂SiF₆:Mn⁴⁺ and KLiSiF₆:Mn⁴⁺.

FIG. 2 shows the emission spectrum of a single-crystal of the inventive luminophore KLiSiF₆:Mn⁴⁺ upon excitation with blue laser light (λ_exc=448 nm). Excitation with blue laser light causes KLiSiF₆:Mn⁴⁺ to show (deep) red luminescence with a typical line spectrum for Mn⁴⁺-doped luminophores. An emission maximum of ≈631 nm means that the emission is also in a preferred range for red luminophores.

Since the electronic transitions for Mn⁴⁺ (d-d transitions) occur in inner, shielded electron shells, the position of the emission bands is not strongly dependent on the environment of the activator in the crystal structure as is the case for Eu