Patent Publication Number: US-2022220375-A1

Title: Manganese-doped red luminescent material and conversion led

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a national stage entry according to 35 U.S.C. §371 of PCT application No.: PCT/EP2020/062960 filed on May 11, 2020; which claims priority to German Patent Application Serial No.: 10 2019 207 046.9 filed on May 15, 2019; all of which are incorporated herein by reference in their entirety and for all purposes. 
    
    
     TECHNICAL FIELD 
     The disclosure relates to a luminophore and to a conversion LED comprising the luminophore in particular. 
     BACKGROUND 
     In white light-emitting conversion LEDs as used in general lighting, the red component of the white overall radiation is produced by the conversion of blue primary light from a semiconductor layer sequence to longer-wave red radiation by means of an inorganic luminophore. A crucial role is played here by the shape and position of the emission band in the red spectral region. The human eye is fundamentally less sensitive to red radiation than to green radiation, for example. The lower the energy or the greater the wavelength in the wavelength range above 555 nm, the worse/more inefficient the perception of red radiation in particular can be. In a white light-emitting conversion LED, however, the red spectral regions, especially the deep red spectral regions with high wavelengths, are particularly important when the conversion LED is to have a high color rendering index (CRI) in combination with high luminous efficacy of radiation (LER) and low correlated color temperature (CCT). Typical red luminophores for these applications are based on Eu 2+  or Ce 3+  emission, these elements being introduced into inorganic host structures in which they then absorb blue light and produce longer-wave emissions. These luminophores generally have broad emission bands. Accordingly, in the case of red-emitting luminophores, many photons are inevitably also converted to those spectral regions (large wavelengths; e.g. &gt;650 nm) that can be perceived only very inefficiently by the human eye. This leads to a severe reduction in efficiency of the conversion LED in relation to eye sensitivity. In order to solve this problem, attempts may be made to shift the emission spectrum to shorter wavelength by variations in the chemical composition of the host structure, i.e. to increase the integral overlap with the eye sensitivity curve. However, the Gaussian distribution of the photons emitted means that this also leads to a reduction in the photon count in the desired red spectral region, and so the abovementioned criteria can no longer be fulfilled. 
     Luminophores such as the nitridolithoaluminate “SrLiAl 3 N 4 :Eu 2+ ” (WO 2013/175336 A1; Narrow-band red-emitting Sr[LiAl 3 N 4 ]:Eu 2+  as a next-generation LED-phosphor material, Nature Materials 2014; P. Pust et al.) already have extremely narrow emission bands with FWHM&lt;55 nm, which leads to a reduction in those converted photons which, in the long-wave region of the visible spectrum (long-wave flank of the emission band), are perceived very inefficiently by the human eye. At the same time, however, the emission maximum of SrLiAl 3 N 4 :Eu 2+  at about 650 nm is already so far into the deep red region that conversion LEDs with this luminophore as the sole red component have barely any efficiency advantage, if any, over solutions with broader-band luminophores. Efficiency losses here are dominant over the CRI gain (R9). Another luminophore, SrMg 3 SiN 4 :Eu 2+  (Toward New Phosphors for Application in Illumination-Grade White pc-LEDs: The Nitridomagnesosilicates Ca[Mg 3 SiN 4 ]:Ce 3+ , Sr[Mg 3 SiN 4 ]:Eu 2+  and Eu[Mg 3 SiN 4],  Chemistry of Materials 2014, S. Schmiechen et al.), shows a blue-shifted, likewise extremely narrow emission band (FWHM&lt;45 nm) that has its emission maximum at about 615 nm and hence within an ideal range for red luminophores. Disadvantageously, this compound shows strong thermal quenching, and so almost no emission can be observed even at room temperature. Use in conversion LEDs is therefore impossible. 
     The shape and position of the emission spectrum depends not only on the chemical composition of the host structure and further factors but also on the nature of the activator ions. The electronic transitions that proceed in the activator ions on absorption and emission then lead to the respective typical emission spectra. For Eu 2+  these are, as described, bands of greater or lesser width. In order to minimize the loss of efficiency resulting from long-wave photons outside the desired range in the case of red luminophores, it is possible to use, for example, Mn 4+ -doped compounds. Since different electronic transitions take place here compared to Eu 2+ , the emission spectrum here features a line character, with the FWHM values of these lines being much smaller (&lt;10 nm) than the corresponding emission bands, for example for Eu 2+ -based luminophores. A material class that has drawn great attention is that of the Mn 4+ -doped hexafluorosilicates. Particular emphasis is given here to the compound K 2 SiF 6 :Mn 4+ . 
     There is thus a great need for red-emitting luminophores having minimum spectral width of emission (“full width at half maximum”, FWHM), in order to keep the number of photons in spectral regions of low eye sensitivity small and at the same time to emit many photons in the desired red spectral region. 
     SUMMARY 
     It is desirable to specify a luminophore that emits radiation in the red spectral region and has a small spectral width of emission. It is desirable to specify a conversion LED comprising the luminophore described here. 
     This object/these objects are achieved by a luminophore and a conversion LED according to the independent claims. 
     Advantageous embodiments and developments are the subject of the respective dependent claims. 
     A luminophore is specified, especially a red-emitting luminophore. 
     In at least one embodiment, the luminophore has the empirical formula A 3 M* c O x F y :Mn 4+  where
         A=Li, Na, Rb, K and/or Cs,   M*=Cr, Mo and/or W,   3+6c=2x+y   0&lt;x, 0&lt;y and   0&lt;c.       

     In at least one embodiment, the luminophore has the empirical formula A 3 M b O x F y :Mn 4+  where
         A=Li, Na, Rb, K and/or Cs,   M=V and/or Nb,   3+5b=2x+y   1&lt;x, 0&lt;y and   0&lt;b.       

     Here and hereinafter, luminophores are described in terms of empirical formulae. In the empirical formulae specified, it is possible that the luminophore includes further elements, for instance in the form of impurities, in which case these impurities taken together should have a maximum proportion by weight in the luminophore of not more than 1 permille or 100 ppm (parts per million) or 10 ppm. 
     A known Mn-doped luminophore is K 2 SiF 6 :Mn 4+ . The emission spectrum of this luminophore features narrow emission bands, with the half-height widths of these emission bands being below 10 nm and hence much smaller than the corresponding emission bands, for example for Eu 2+ -doped luminophores. K 2 SiF 6 :Mn 4+  has a peak wavelength of 631 nm and is prepared by a precipitation reaction in aqueous hydrofluoric acid (HF) (Efficient Mn (IV) Emission in Fluorine Coordination, A. G. Paulusz, J. Electrochem. Soc.: Solid-State Science and Technology 1973, 942). Reactants used are, for example, K 2 CO 3  or KF (also formed by dissolution of K 2 CO 3  in HF), and also SiO 2  and a manganese source. 
     The inventors of the present application have surprisingly succeeded in preparing Mn 4+ -doped oxo fluorides which, when excited with a primary radiation, show emission or secondary radiation with a peak wavelength in the red spectral region between about 625 nm to 635 nm. It is known from the literature that Mn 4+ -doped oxidic compounds fundamentally emit at greater wavelengths than the corresponding fluoridic compounds [A. review on Mn 4+  activators in solids for warm white light-emitting diodes, RSC Advances 2016, Chen et al.; Research progress and application prospects of transition metal Mn 4+ -activated luminescent materials, Journal of Materials Chemistry C 2016, Zhou et al.] With the peak wavelength of the Mn-doped oxo fluorides which is thus at surprisingly short wavelength, the emission is advantageously within a range for red luminophores. By virtue of the position of the peak wavelength and the simultaneously small half-height width of the emission bands, many photons are advantageously emitted in the desired visible red spectral region, and the converted photons in the long-wave red region of the visible spectrum that are perceived very inefficiently by the human eye are kept to a low level. This means that the luminophores are of excellent suitability for a conversion LED that emits white overall radiation since it is possible to achieve a high color rendering index (R9) and a high luminous efficacy of radiation (LER) of the overall radiation. In addition, the luminophores may be used in background lighting devices suitable for representation of large color spaces, for example displays. 
     Peak wavelength or emission maximum refers in the present context to the wavelength in the emission spectrum of a luminophore at which the intensity is at its maximum within the emission spectrum. 
     In at least one embodiment, the luminophore has the empirical formula A 3 M*O x F 9−2x :Mn 4+  where
         A=Li, Na, Rb, K and/or Cs,   M*=Cr, Mo and/or W,       

     and
         0&lt;x&lt;4.5.       

     In at least one embodiment, the luminophore has the empirical formula A 3 M*O x F 9−2x :Mn 4+  where
         A=Li, Na, Rb, K and/or Cs,   M*=Cr, Mo and/or W,       

     and
         x=1, x=2, x=3 or x=4, such as x=1. The luminophore having a proportion of oxygen x=1 has been found to be particularly efficient and stable.       

     In at least one embodiment, the luminophore has the empirical formula (K 1−z A* z ) 3 M*O x F 9−2x :Mn 4+  where
         A*=Li, Na, Rb, K and/or Cs,   M*=Cr, Mo and/or W,   0≤z≤1, such as 0≤z≤1 and   x=1, x=2, x=3 or x=4.       

     In at least one embodiment, the luminophore has the empirical formula K 3 M*O x F 9−2x :Mn 4+  where
         M*=Cr, Mo and/or W and   x=1, x=2, x=3 or x=4, such as x=1.       

     In at least one embodiment, the luminophore has the empirical formula K 3 M*OF 7 :Mn 4+  where
         M*=Cr, Mo and/or W, such as M*=Mo or W.       

     In at least one embodiment, the luminophore has the empirical formula A 3 M b O x F 8−2x :Mn 4+  where
         A=Li, Na, Rb, K and/or Cs,   M=V and/or Nb,       

     and
         1&lt;x&lt;4.       

     In at least one embodiment, the luminophore has the empirical formula A 3 M x O x F 8−2x :Mn 4+  where
         A=Li, Na, Rb, K and/or Cs,   M=V and/or Nb,       

     and
         x=2 or x=3, such as x=2. The luminophore having a proportion of oxygen x=2 has been found to be particularly efficient and stable.       

     In at least one embodiment, the luminophore has the empirical formula (K 1−z A* z ) 3 MO x F 8−2x :Mn 4+  where
         A*=Li, Na, Rb and/or Cs,   M=V and/or Nb,   0 z 1 and   x=2 or x=3, such as x=2.       

     In at least one embodiment, the luminophore has the empirical formula (K 1−z A* z ) 3 MO x F 8−2x :Mn 4+  where
         M=V and/or Nb,   0&lt;z≤⅔ and   x=2 or x=3, such as x=2. Particularly luminophores including K and Na have been found to be particularly stable and efficient.       

     In at least one embodiment, the luminophore has the empirical formula (K 1−z Na z ) 3 MO 2 F 4 :Mn 4+  where
         M=V and/or Nb, such as M=Nb and   0&lt;z≤⅔, such as z=⅓.       

     Mn 4+ , in a further embodiment, may be present in molar percentages between 0.1 mol % and 10 mol %, 0.5 mol % to 8 mol % or 1 mol % to 6 mol %. 
     In at least one embodiment, the luminophore is capable of absorbing primary radiation from the UV to blue spectral region and converting it to secondary radiation within the red spectral region. 
     Moreover, the luminophore in at least one embodiment has a half-height width of the emission bands below 15 nm. More particularly, the half-height width of the emission band with the maximum intensity (emission maximum, peak wavelength) is below 15 nm. 
     The half-height width (FWHM, full width at half maximum) is understood here and hereinafter to mean the spectral width at half the height of the maximum emission peak or an emission band or emission line. 
     The luminophores K 3 MoOF 7 :Mn 4+ , K 3 WOF 7 :Mn 4+  and K 2 NaNbO 2 F 4 :Mn 4+ , for example on excitation with primary radiation from the UV to blue spectral region, emit secondary radiation having a peak wavelength in the red spectral region at about 630 nm. The emission bands of the luminophores have a small half-height width and hence a high light yield on account of a large overlap with the human eye sensitivity curve having a maximum at 555 nm. It is thus possible to use these luminophores to provide particularly efficient conversion LEDs. 
     A luminophore composition comprising a luminophore described here and an inorganic compound. All details and definitions of the luminophore are also applicable to the luminophore composition, and vice versa. 
     In at least one embodiment, the luminophore in the luminophore composition has the empirical formula K 3 M*O x F 9−2x :Mn 4+  where
         M*=Cr, Mo and/or W and   x=1, x=2, x=3 or x=4, such as x=1. More particularly, the inorganic compound is KHF 2.          

     In at least one embodiment, the luminophore in the luminophore composition has the empirical formula K 3 MoOF 7 :Mn 4+  and the inorganic compound is KHF 2 . 
     A conversion LED may include the luminophore or luminophore composition. All details and definitions of the luminophore and of the luminophore composition are also applicable to the conversion LED, and vice versa. 
     In at least one embodiment, the conversion LED has a semiconductor layer sequence. The semiconductor layer sequence is set up for emission of electromagnetic primary radiation. 
     In at least one embodiment, the semiconductor layer sequence includes at least one III-V compound semiconductor material. 
     The semiconductor material is, for example, a nitride compound semiconductor material, such as Al n In 1−n−m Ga m N where, in each case, 0≤n≤1, 0≤m≤1 and n+m≤1. The semiconductor layer sequence may include 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 they may be partially replaced and/or supplemented by small amounts of further substances. More particularly, the semiconductor layer sequence is formed from InGaN. 
     The semiconductor layer sequence includes 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 generated in the active layer. A wavelength or the emission maximum of the radiation is within the ultraviolet and/or visible region, especially at wavelengths between 300 nm and 470 nm inclusive. 
     The conversion LED is set up to emit white or colored light. 
     In combination with the luminophore present in the conversion LED, the conversion LED is set up 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, such as in general lighting or background lighting, for example of displays suitable for representation of large color spaces. 
     The conversion LED has a conversion element. More particularly, the conversion element comprises or consists of the luminophore. The luminophore at least partly or fully converts electromagnetic primary radiation to electromagnetic secondary radiation in the red spectral region. 
     In at least one embodiment, the conversion element or conversion LED does not include any further luminophore aside from the luminophore. The conversion element may also consist of the luminophore. The luminophore may be set up 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 includes a further red-emitting luminophore as well as the luminophore. The conversion element may also consist of the luminophore and the further red-emitting luminophore. The luminophores may be set up 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[Al 2 Li 2 O 2 N 2 ]:Eu. Sr[Al 2 Li 2 O 2 N 2 ]:Eu can crystallize in the tetragonal space group P4 2 /m. The further luminophore advantageously allows the color locus of the overall radiation to be adjusted as required. In addition, this can achieve particularly high color saturation and efficiency that typically cannot be achieved through the use of just one luminophore. 
     In at least one embodiment, the conversion element includes a second and/or third luminophore as well as the luminophore. The conversion element may comprise further luminophores as well as the luminophore and the second and third luminophores. For example, the luminophores are embedded in a matrix material. Alternatively, the luminophores may also be present in a converter ceramic. 
     The conversion LED may include a second luminophore for emission of radiation from the green spectral region. 
     Additionally or alternatively, the conversion LED may include a third luminophore. The third luminophore may be set up for emission of radiation from the yellow spectral region. In other words, the conversion LED may then include at least three luminophores: a yellow-emitting luminophore, a green-emitting luminophore and the red-emitting luminophore. The conversion LED is set up for full conversion or partial conversion, with the primary radiation in the case of full conversion being 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 in that case is especially white mixed radiation. 
     Additionally or alternatively, the conversion LED may include a fourth luminophore. The fourth luminophore may be set up to emit radiation from the blue spectral region. In that case, the conversion LED may comprise at least three luminophores: a blue-emitting luminophore, a green-emitting luminophore and the red-emitting luminophore. The conversion LED is set up for full conversion, with the primary radiation in the case of full conversion being selected from the UV spectral region. The resulting overall radiation from the conversion LED in that case is especially white mixed radiation. 
     Yellow, blue and green luminophores are known to the person skilled in the art and are not listed here separately. 
     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 truer, or truer to nature, the color impression perceived. 
     Working Examples 
     The first working example (WE1) of the luminophore having the empirical formula K 3 MoOF 7 :Mn 4+  was prepared by means of a solid-state synthesis. This involved first synthesizing K 3 MoOF 7  in a weld-sealed Cu ampoule at 300° C. from the reactants KHF 2  and MoO 3  in a molar ratio of 4:1. This was done by heating the oven containing the Cu ampoule at a heating rate of 3° C./min to 300° C. and keeping it at that temperature for 96 h, then cooling at a cooling rate of 0.1° C./min to 250° C. and maintaining that temperature for 24 h, followed by cooling at a cooling rate of 0.1° C./min to 100° C., after which the oven was switched off. In a next step, K 3 MoOF 7  was reacted with an Mn source in a ball mill in order to dope it with the Mn 4+  activator. The resultant K 3 MoOF 7  was subjected to ball milling with K 2 MnF 6  (molar ratio 1:0.04) for 6×10 min at 300 rpm in the ball mill with 15 min breaks between the runs. The energy introduced by the grinding balls is sufficient to bring about replacement of Mo by Mn in the structure. This step leaves a homogeneously red-glowing material. Studies by means of x-ray powder methods show that the luminophore can be prepared in good quality (see  FIG. 4 ), and that the phase components in the powder are not altered by the ball milling process (see  FIG. 5 ). 
     Table 1 shows data from single-crystal x-ray structure analysis of WE1. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
            
               
                   
                 Empirical formula 
                 K 3 MoOF 7 :Mn 4+   
               
               
                   
                 Molar mass/g mol −1   
                 362.22     
               
               
                   
                 Temperature/K 
                 193(2)     
               
               
                   
                 Crystal system 
                 triclinic 
               
               
                   
                 Space group 
                 P -1 (No. 2) 
               
               
                   
                 a/Å 
                 6.7602(4) 
               
               
                   
                 b/Å 
                 8.1443(5) 
               
               
                   
                 c/Å 
                 8.3106(5) 
               
               
                   
                 α/° 
                 115.242(2)   
               
               
                   
                 β/° 
                 90.582(2)  
               
               
                   
                 γ/° 
                 92.732(2)  
               
               
                   
                 Volume/Å 3   
                 413.16(4)   
               
               
                   
                 Z 
                 2      
               
               
                   
                 ρ calc /g cm −3   
                 2.912    
               
               
                   
                 μ/mm −1   
                 3.167    
               
               
                   
                 F(000) 
                 340       
               
               
                   
                 Crystal size/mm 3   
                 0.045 × 0.025 × 0.015 
               
               
                   
                 Radiation 
                 Mo-K α  (λ = 0.71073 Å) 
               
               
                   
                 2θ angle range/° 
                 5.422 to 54.998 
               
               
                   
                 hkl range 
                 −8 &lt; h &lt; 8, −10 &lt; k &lt; 
               
               
                   
                   
                 10, −10 &lt; l &lt; 10 
               
               
                   
                 Reflections measured 
                 9825        
               
               
                   
                 Independent reflections 
                 1893 [R int  = 0.0436, 
               
               
                   
                   
                 R σ  = 0.0325] 
               
               
                   
                 Restraints/parameter 
                 0/109 
               
               
                   
                 Goodness-of-fit for F 2   
                 1.154    
               
               
                   
                 R values (I ≥ 2σ(I)) 
                 R 1  = 0.0336, wR 2  = 0.0797 
               
               
                   
                 R values (all data) 
                 R 1  = 0.0423, wR 2  = 0.0802 
               
               
                   
                 Residual electron density 
                 1.273/−1.006 
               
               
                   
                 (max/min)/e Å −3   
               
               
                   
                   
               
            
           
         
       
     
     Table 2 shows position parameters, isotropic deflection parameters and position population in K 3 MoOF 7 :Mn 4+  (WE1). 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                   
                   
                 Pop- 
               
               
                   
                   
                   
                   
                   
                 ula- 
               
               
                 Atom 
                 x 
                 y 
                 z 
                 U iso   
                 tion 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Mo1 
                 0.74983(6) 
                 0.66747(6) 
                 0.83581(5) 
                 0.01404(12) 
                 1 
               
               
                 K1 
                 0.70976(15) 
                 0.62877(13) 
                 0.34024(14) 
                 0.0181(2) 
                 1 
               
               
                 K2 
                 0.78846(14) 
                 0.16025(13) 
                 0.34678(13) 
                 0.0168(2) 
                 1 
               
               
                 K3 
                 0.23318(15) 
                 0.83983(14) 
                 0.12107(13) 
                 0.0186(2) 
                 1 
               
               
                 F1 
                 1.0306(4) 
                 0.6289(4) 
                 0.7996(4) 
                 0.0210(6) 
                 1 
               
               
                 F2 
                 0.6906(4) 
                 0.4693(4) 
                 0.6054(4) 
                 0.0261(7) 
                 1 
               
               
                 F3 
                 0.4797(4) 
                 0.7255(4) 
                 0.8361(4) 
                 0.0249(6) 
                 1 
               
               
                 F4 
                 0.8147(5) 
                 0.8905(4) 
                 1.0234(4) 
                 0.0324(7) 
                 1 
               
               
                 F5 
                 0.7995(4) 
                 0.8057(4) 
                 0.6841(3) 
                 0.0182(6) 
                 1 
               
               
                 O1 
                 0.7213(5) 
                 0.5402(5) 
                 0.9510(5) 
                 0.0266(8) 
                 1 
               
               
                 F6 
                 0.0087(4) 
                 0.8646(4) 
                 0.3817(4) 
                 0.0220(6) 
                 1 
               
               
                 F7 
                 0.5229(4) 
                 0.9093(4) 
                 0.3566(4) 
                 0.0250(6) 
                 1 
               
               
                   
               
            
           
         
       
     
     Table 3 shows anisotropic deflection parameters in K 3 MoOF 7 :Mn 4+  (WE1) . 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Atom 
                 U 11   
                 U 22   
                 U 33   
                 U 23   
                 U 13   
                 U 12   
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Mo1 
                 0.01225(19) 
                 0.0177(2) 
                 0.0180(2) 
                 0.01297(17) 
                 0.00232(14) 
                 0.00178(14) 
               
               
                 K1 
                 0.0192(5) 
                 0.0136(5) 
                 0.0200(5) 
                 0.0057(4) 
                 0.0001(4) 
                 0.0017(4) 
               
               
                 K2 
                 0.0197(5) 
                 0.0160(5) 
                 0.0161(5) 
                 0.0083(4) 
                 −0.0003(4) 
                 0.0017(4) 
               
               
                 K3 
                 0.0232(5) 
                 0.0181(5) 
                 0.0140(5) 
                 0.0060(4) 
                 0.0025(4) 
                 0.0041(4) 
               
               
                 F1 
                 0.0129(12) 
                 0.0238(15) 
                 0.0264(15) 
                 0.0105(12) 
                 0.0021(11) 
                 0.0041(11) 
               
               
                 F2 
                 0.0261(15) 
                 0.0181(15) 
                 0.0224(16) 
                 −0.0025(12) 
                 0.0024(12) 
                 0.0015(12) 
               
               
                 F3 
                 0.0156(13) 
                 0.0307(16) 
                 0.0270(16) 
                 0.0104(13) 
                 0.0050(11) 
                 0.0074(12) 
               
               
                 F4 
                 0.0431(19) 
                 0.0251(17) 
                 0.0211(16) 
                 0.0018(13) 
                 −0.0028(14) 
                 0.0077(14) 
               
               
                 F5 
                 0.0242(14) 
                 0.0172(14) 
                 0.0160(14) 
                 0.0099(11) 
                 0.0012(11) 
                 0.0001(11) 
               
               
                 O1 
                 0.032(2) 
                 0.033(2) 
                 0.030(2) 
                 0.0271(18) 
                 0.0080(16) 
                 0.0048(16) 
               
               
                 F6 
                 0.0222(14) 
                 0.0225(15) 
                 0.0220(15) 
                 0.0104(13) 
                 0.0037(11) 
                 −0.0014(12) 
               
               
                 F7 
                 0.0221(14) 
                 0.0246(15) 
                 0.0295(17) 
                 0.0123(13) 
                 −0.0008(12) 
                 0.0052(12) 
               
               
                   
               
            
           
         
       
     
     Table 4 shows a comparison of the optical data of K 3 MoOF 7 :Mn 4+  and K 2 SiF 6 :Mn 4+   
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 λ dom */ 
                 λ max / 
                   
                   
                 LER/lm 
               
               
                   
                 nm 
                 nm 
                 x CIE   
                 y CIE   
                 W opt   −1   
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 K 3 MoOF 7 :Mn 4+   
                 619 
                 627 
                 0.690(1) 
                 0.310(1) 
                 218 
               
               
                 K 2 SiF 6 :Mn 4+   
                 621 
                 631 
                 0.693(1) 
                 0.307(1) 
                 204 
               
               
                   
               
               
                 *dominant wavelength 
               
            
           
         
       
     
     The dominant wavelength is a means of describing non-spectral (polychromatic) mixtures of light in terms of spectral (monochromatic) light perceived to be of a similar shade. In the CIE color space, the line that connects a point for a particular color and the point xCIE=0.333, yCIE=0.333 can be extrapolated such that it meets the outline of the space at two points. The point of intersection closer to said color represents the dominant wavelength of the color as the wavelength of the pure spectral color at this point of intersection. The dominant wavelength is thus the wavelength perceived by the human eye. 
     Since the electronic transitions for Mn 4+  (d-d transitions) take place in inner shielded electron shells, the position of the emission band is not, as in the case of Eu 2+ -based luminophores, highly dependent on the environment of the activator in the crystal structure. Thus, the result is always (deep) red emission when Mn 4+  is surrounded by six O/F atoms (in the form of an octahedron) in the structure. However, slight variations in emission can be achieved via the atomic number of the counterions in the structure and via the absolute symmetry of the Mn octahedra, for example. Since the eye sensitivity curve in the region of this present emission maximum (λ max ˜630 nm) of K 3 MoOF 7 :Mn 4+  and K 2 SiF 6 :Mn 4+  has a large (negative) slope, even a small shift in the emission band (CIE color coordinates x CIE  and y CIE ) results in distinctly different luminous efficacy of radiation (LER), as shown in Table 4. K 3 MoOF 7 :Mn 4+  with LER elevated by 7% compared to K 2 SiF 6 :Mn 4+  was prepared by a novel two-stage synthesis method. The luminophore also shows a different crystal structure than the reference material K 2 SiF 6 :Mn 4+ . The inventive luminophore WE1 may, advantageously with respect to K 2 SiF 6 :Mn 4+ , be used for solutions in the field of white conversion LEDs having particularly high color rendering index, especially in combination with high R9 value, for example in general lighting or in background lighting devices that are suitable for representation of large color spaces, for example in displays. 
     The second working example (WE2) of the luminophore having the empirical formula K 3 WOF 7 :Mn 4+  was prepared by means of a solid-state synthesis. This involved first synthesizing K 3 WOF 7  in a weld-sealed Cu ampoule at 400° C. from the reactants KHF 2  and W03 in a molar ratio of 3:1. This was done by heating the oven containing the Cu ampoule at a heating rate of 3° C./min to 400° C. and keeping it at that temperature for 48 h, then cooling at a cooling rate of 0.1° C./min to 350° C. and then switching off the oven. In a next step, K 3 WOF 7  was reacted with an Mn source in a ball mill in order to dope it with the activator Mn 4+ . The resultant K 3 WOF 7  was subjected to ball milling with K 2 MnF 6  (molar ratio 1:0.04) for 6×10 min at 300 rpm in the ball mill with 15 min breaks between the runs. The energy introduced by the grinding balls is sufficient to bring about replacement of W by Mn in the structure. This step leaves a homogeneously red-glowing material. Studies by means of x-ray powder methods show that the luminophore can be prepared in good quality (see  FIG. 9 ), and that the phase components in the powder are not altered by the ball milling process (see  FIG. 10 ). 
     Table 5 shows data from single-crystal x-ray structure analysis of WE2. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 5 
               
               
                   
                   
               
             
            
               
                   
                 Empirical formula 
                 K 3 WOF 7: Mn 4+   
               
               
                   
                 Molar mass/g mol −1   
                 450.15     
               
               
                   
                 Temperature/K 
                 186(2)     
               
               
                   
                 Crystal system 
                 monoclinic 
               
               
                   
                 Space group 
                 P2 1 /c (No. 14) 
               
               
                   
                 a/Å 
                 8.8415(4) 
               
               
                   
                 b/Å 
                 13.7986(6)  
               
               
                   
                 c/Å 
                 6.7970(3) 
               
               
                   
                 β/° 
                 93.0410(10) 
               
               
                   
                 Volume/Å 3   
                 828.07(6)   
               
               
                   
                 Z 
                 4      
               
               
                   
                 ρ calc /g cm −3   
                 3.611    
               
               
                   
                 μ/mm −1   
                 15.527    
               
               
                   
                 F(000) 
                 808       
               
               
                   
                 Crystal size/mm 3   
                 0.04 × 0.03 × 0.015 
               
               
                   
                 Radiation 
                 Mo-Kα (λ = 0.71073 Å) 
               
               
                   
                 2θ angle range/° 
                 4.614 to 69.982 
               
               
                   
                 hkl range 
                 −14 &lt; h &lt; 14, −22 &lt; k &lt; 
               
               
                   
                   
                 22, −10 &lt; l &lt; 10 
               
               
                   
                 Reflections measured 
                 63868       
               
               
                   
                 Independent reflections 
                 3643 [R int  = 0.0490, 
               
               
                   
                   
                 R σ  = 0.0290] 
               
               
                   
                 Restraints/parameter 
                 0/109 
               
               
                   
                 Goodness-of-fit for F 2   
                 1.105    
               
               
                   
                 R values (I ≥ 2σ(I)) 
                 R 1  = 0.0253, wR 2  = 0.0495 
               
               
                   
                 R values (all data) 
                 R 1  = 0.0334, wR 2  = 0.0515 
               
               
                   
                 Residual electron density 
                 3.603/−3.178 
               
               
                   
                 (max/min)/e Å −3   
               
               
                   
                   
               
            
           
         
       
     
     Table 6 shows position parameters, isotropic deflection parameters and position population in K 3 WOF 7 :Mn 4+  (WE2). 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 6 
               
               
                   
               
               
                   
                   
                   
                   
                   
                 Pop- 
               
               
                   
                   
                   
                   
                   
                 ula- 
               
               
                 Atom 
                 x 
                 y 
                 z 
                 U iso   
                 tion 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 W1 
                 0.74918(2) 
                 0.57684(2) 
                 0.25859(2) 
                 0.01365(3) 
                 1 
               
               
                 K1 
                 0.52953(8) 
                 0.64690(5) 
                 0.77694(10) 
                 0.01690(13) 
                 1 
               
               
                 K2 
                 −0.02633(8) 
                 0.85314(5) 
                 1.22034(10) 
                 0.01681(13) 
                 1 
               
               
                 K3 
                 1.24774(9) 
                 0.59684(5) 
                 0.21794(11) 
                 0.01794(12) 
                 1 
               
               
                 F1 
                 0.7535(4) 
                 0.70569(18) 
                 0.2558(4) 
                 0.0309(6) 
                 0.5 
               
               
                 F2 
                 0.7159(3) 
                 0.5586(2) 
                 0.5122(3) 
                 0.0264(5) 
                 0.5 
               
               
                 F3 
                 0.7833(2) 
                 0.57470(17) 
                 −0.0292(3) 
                 0.0200(4) 
                 1 
               
               
                 F4 
                 0.5405(2) 
                 0.56814(19) 
                 0.1737(3) 
                 0.0242(5) 
                 1 
               
               
                 F5 
                 0.9613(2) 
                 0.56142(19) 
                 0.2993(4) 
                 0.0269(5) 
                 1 
               
               
                 F6 
                 0.7482(3) 
                 0.43429(15) 
                 0.2101(4) 
                 0.0224(4) 
                 1 
               
               
                 F7 
                 0.3780(3) 
                 0.77159(18) 
                 0.9789(3) 
                 0.0248(5) 
                 1 
               
               
                 F8 
                 0.1279(3) 
                 0.74494(19) 
                 0.9957(3) 
                 0.0260(5) 
                 1 
               
               
                 O1 
                 0.7535(4) 
                 0.70569(18) 
                 0.2558(4) 
                 0.0309(6) 
                 0.5 
               
               
                 O2 
                 0.7159(3) 
                 0.5586(2) 
                 0.5122(3) 
                 0.0264(5) 
                 0.5 
               
               
                   
               
            
           
         
       
     
     Table 7 shows anisotropic deflection parameters in K 3 WOF 7 :Mn 4+  (WE2). 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 7 
               
               
                   
               
               
                 Atom 
                 U 11   
                 U 22   
                 U 33   
                 U 23   
                 U 13   
                 U 12   
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 W1 
                 0.01517(5) 
                 0.01271(5) 
                 0.01320(5) 
                 −0.00098(4) 
                 0.00188(3) 
                 −0.00095(5) 
               
               
                 K1 
                 0.0135(3) 
                 0.0192(3) 
                 0.0181(3) 
                 0.0013(2) 
                 0.0020(2) 
                 0.0028(2) 
               
               
                 K2 
                 0.0138(3) 
                 0.0172(3) 
                 0.0196(3) 
                 −0.0005(2) 
                 0.0019(2) 
                 0.0026(2) 
               
               
                 K3 
                 0.0136(3) 
                 0.0149(3) 
                 0.0253(3) 
                 −0.0014(2) 
                 0.0010(2) 
                 −0.0004(2) 
               
               
                 F1 
                 0.0365(14) 
                 0.0127(10) 
                 0.0448(16) 
                 −0.0035(11) 
                 0.0141(12) 
                 −0.0001(12) 
               
               
                 F2 
                 0.0255(12) 
                 0.0397(16) 
                 0.0143(10) 
                 0.0029(9) 
                 0.0052(8) 
                 0.0012(11) 
               
               
                 F3 
                 0.0228(10) 
                 0.0266(11) 
                 0.0109(8) 
                 0.0008(7) 
                 0.0054(7) 
                 0.0000(9) 
               
               
                 F4 
                 0.0090(9) 
                 0.0354(13) 
                 0.0281(11) 
                 0.0018(9) 
                 −0.0010(7) 
                 0.0010(9) 
               
               
                 F5 
                 0.0105(9) 
                 0.0334(14) 
                 0.0367(13) 
                 −0.0006(10) 
                 −0.0001(8) 
                 −0.0007(9) 
               
               
                 F6 
                 0.0196(9) 
                 0.0110(9) 
                 0.0368(12) 
                 −0.0019(8) 
                 0.0018(9) 
                 −0.0007(8) 
               
               
                 F7 
                 0.0217(11) 
                 0.0290(12) 
                 0.0236(10) 
                 −0.0088(9) 
                 0.0009(8) 
                 0.0012(9) 
               
               
                 F8 
                 0.0200(11) 
                 0.0301(12) 
                 0.0279(11) 
                 −0.0101(9) 
                 0.0021(8) 
                 0.0012(9) 
               
               
                 O1 
                 0.0365(14) 
                 0.0127(10) 
                 0.0448(16) 
                 −0.0035(11) 
                 0.0141(12) 
                 −0.0001(12) 
               
               
                 O2 
                 0.0255(12) 
                 0.0397(16) 
                 0.0143(10) 
                 0.0029(9) 
                 0.0052(8) 
                 0.0012(11) 
               
               
                   
               
            
           
         
       
     
     Table 8 shows a comparison of the optical date of K 3 WOF 7 :Mn 4+  and K 2 Si F 6 :Mn 4+   
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 8 
               
               
                   
                   
               
               
                   
                 λ dom / 
                 λ max / 
                   
                   
                 LER/lm 
               
               
                   
                 nm 
                 nm 
                 x CIE   
                 y CIE   
                 W opt   −1   
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 K 3 WOF 7 :Mn 4+   
                 619 
                 627 
                 0.689(1) 
                 0.311(1) 
                 225 
               
               
                 K 2 SiF 6 :Mn 4+   
                 621 
                 631 
                 0.693(1) 
                 0.307(1) 
                 204 
               
               
                   
               
            
           
         
       
     
     Since the electronic transitions for Mn 4+  (d-d transitions) take place in inner shielded electron shells, the position of the emission band is not, as in the case of Eu 2+ -based luminophores, highly dependent on the environment of the activator in the crystal structure. Thus, the result is always (deep) red emission when Mn 4+  is surrounded by six O/F atoms (in the form of an octahedron) in the structure. However, slight variations in emission can be achieved via the atomic number of the counterions in the structure and via the absolute symmetry of the Mn octahedra, for example. Since the eye sensitivity curve in the region of this present emission maximum (λ max ˜630 nm) of K 3 MoOF 7 :Mn 4+  and K 2 SiF 6 :Mn 4+  has a large (negative) slope, even a small shift in the emission band (CIE color coordinates x CIE  and y CIE ) results in distinctly different luminous efficacy of radiation (LER), as shown in Table 8. K 3 WOF 7 :Mn 4+  with LER elevated by 10% compared to K 2 SiF 6 :Mn 4+  was prepared by a novel two-stage synthesis method. The luminophore also shows a different crystal structure than the reference material K 2 SiF 6 :Mn 4+ . The inventive luminophore WE2 may, advantageously with respect to K 2 SiF 6 :Mn 4+ , be used for solutions in the field of white conversion LEDs having particularly high color rendering index, especially in combination with high R9 value, for example in general lighting or in background lighting devices that are suitable for representation of large color spaces, for example in displays. 
     The third working example (WE3) of the luminophore having the empirical formula K 2 NaNbO 2 F 4 :Mn 4+  was prepared by means of a solid-state synthesis. This involved first synthesizing K 2 NaNbO 2 F 4  in a weld-sealed Cu ampoule at 300° C. from the reactants KHF 2,  NaHF 2  and Nb2O 5  in a molar ratio of 3:3:2. This was done by heating the oven containing the Cu ampoule at a heating rate of 3° C./min to 300° C. and keeping it at that temperature for 1 h, then cooling at a cooling rate of 0.1° C./min to 100° C., and then the oven was switched off. The resultant K 2 NaNbO 2 F 4  crystals are also suitable for phase analysis by means of powder x-ray diffraction (see  FIG. 15 ). In a next step, K 2 NaNbO 2 F 4  was reacted with an Mn source in a ball mill in order to dope it with the activator Mn 4+ . The resultant K 2 NaNbO 2 F 4  was subjected to ball milling with Cs 2 MnF 6  (molar ratio 1:0.04) for 6×10 min at 300 rpm in the ball mill with 15 min breaks between the runs. The energy introduced by the grinding balls is sufficient to bring about replacement of Nb by Mn in the structure. This step leaves a homogeneously red-glowing material. Studies by means of x-ray powder methods show that the luminophore can be prepared in good quality (see  FIG. 15 ), and that the phase proportions in the powder are not altered by the ball milling process (see  FIG. 16 ). 
     Table 9 shows data from Rietveld analysis of WE3. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 9 
               
               
                   
                   
               
             
            
               
                   
                 Empirical formula 
                 K 2 NaNbO 2 F 4 :Mn 4+   
               
               
                   
                 Molar mass/g mol −1   
                 302.10 
               
               
                   
                 Temperature/K 
                 296 
               
               
                   
                 Crystal system 
                 cubic 
               
               
                   
                 Space group 
                 Fm-3m (No. 225) 
               
               
                   
                 a/Å 
                 8.504(4) 
               
               
                   
                 Volume/Å 3   
                 615.0(8) 
               
               
                   
                 Z 
                 4 
               
               
                   
                 ρ calc /g cm −3   
                 3.263(4) 
               
               
                   
                 μ/cm −1   
                 36.963(5) 
               
               
                   
                 Radiation 
                 Mo-K α1  (λ = 0.7093 Å) 
               
               
                   
                 2θ angle range/° 
                 2.00 to 41.89 
               
               
                   
                 Peak type 
                 PV-TCHZ 
               
               
                   
                 Data points 
                 2660 
               
               
                   
                 Background function 
                 Chebyshev polynomial (12 
               
               
                   
                   
                 parameters) 
               
               
                   
                 Number of independent 
                 26 
               
               
                   
                 parameters 
               
               
                   
                 Goodness of fit 
                 3.31 
               
               
                   
                 R values 
                 R p  = 0.0836 
               
               
                   
                   
                 R wp  = 0.1267 
               
               
                   
                   
                 R exp  = 0.0383 
               
               
                   
                   
               
            
           
         
       
     
     Table 10 shows position parameters, isotropic deflection parameters and position population in K 2 NaNbO 2 F 4 :Mn 4+ . 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 10 
               
               
                   
                   
               
               
                   
                 Atom 
                 x 
                 y 
                 z 
                 B eq   
                 Population 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 Nb1 
                 1 
                 0.5 
                 1 
                 1.879 
                 1 
               
               
                   
                 K1 
                 0.75 
                 0.75 
                 0.75 
                 2.171 
                 1 
               
               
                   
                 Na1 
                 1 
                 0.5 
                 0.5 
                 1.161 
                 1 
               
               
                   
                 O1 
                 1 
                 0.5 
                 0.78431(46) 
                 2.929 
                 0.33 
               
               
                   
                 F1 
                 1 
                 0.5 
                 0.78431(46) 
                 2.929 
                 0.67 
               
               
                   
                   
               
            
           
         
       
     
     Table 11 shows a comparison of the optical data of K 2 NaNbO 2 F 4 :Mn 4+  and K 2 SiF 6 :Mn 4+   
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 11 
               
               
                   
                   
               
               
                   
                 λ dom / 
                 λ max / 
                   
                   
                 LER/lm 
               
               
                   
                 nm 
                 nm 
                 x CIE   
                 y CIE   
                 W opt   −1   
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 K 2 NaNbO 2 F 4 :Mn 4+   
                 624 
                 632 
                 0.699(1) 
                 0.300(1) 
                 197 
               
               
                 (powder) 
               
               
                 K 2 NaNbO 2 F 4 :Mn 4+   
                 622 
                 633 
                 0.695(1) 
                 0.305(1) 
                 200 
               
               
                 (single grain) 
               
               
                 K 2 SiF 6 :Mn 4+   
                 621 
                 631 
                 0.693(1) 
                 0.307(1) 
                 204 
               
               
                   
               
            
           
         
       
     
     Contrary to expectation, the inventive luminophore K 2 NaNbO 2 F 4 :Mn 4+  shows similar emission to the reference material K 2 SiF 6 :Mn 4+ , even though there are oxygen atoms in the first coordination sphere of the Mn 4+  activator. Review articles in the literature show clearly that oxides always emit at longer wavelengths than the corresponding fluorides [A review on Mn 4+  activators in solids for warm white light-emitting diodes, RSC Advances 2016, Chen et al.]; 
     Research progress and application prospects of transition metal Mn 4+ -activated Luminescent materials, Journal of Materials Chemistry C 2016, Zhou et al.) The inventive luminophore WE3 may, advantageously with respect to K 2 SiF 6 :Mn 4+ , be used for solutions in the field of white conversion LEDs having particularly high color rendering index, specifically in combination with high R9 value, for example in general lighting or in background lighting devices suitable for representing large color spaces, for example in displays. In the synthesis of K 2 NaNbO 2 F 4 :Mn 4+ , by contrast with the synthesis of K 2 SiF 6 :Mn 4+ , no HF is used, which drastically reduces the necessary safety precautions in production and hence can simultaneously distinctly lower the costs for the synthesis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantageous embodiments and developments will be apparent from the working examples described hereinafter in conjunction with the figures. Identical, similar or equivalently functioning elements are labelled with the same reference signs in the figures. The figures and the relative proportions of the elements represented in the figures are not to be considered to be true to scale. Instead, individual elements may be shown exaggerated in size for ease of visualization and/or better understanding. 
         FIG. 1A  shows a unit cell with adjoining polyhedra of the first working example K 3 MoOF 7 :Mn 4+  (WE1) of the luminophore (space group No. 2; P-1). 
         FIG. 1B  shows a unit cell of cubic K 2 SiF 6 :Mn 4+  (space group No. 225; Fm-3m). 
         FIG. 2  shows an emission spectrum of WE1 (powder sample) on excitation with blue primary radiation (λ exc =460 nm). 
         FIG. 3  shows the excitation spectrum of WE1 based on the emission maximum at 627 nm. 
         FIG. 4  shows a Rietveld refinement of a powder sample of K 3 MoOF 7 :Mn 4+  (WE1). 
         FIG. 5  shows a PXRD comparison (Mo—K α1  radiation) of K 3 MoOF 7  and K 3 MoOF 7 :Mn 4+  (WE1). 
         FIG. 6  shows a unit cell of the second working example K 3 WOF 7 :Mn 4+  (WE2) of the luminophore (space group No. 14; P2 1 /c). 
         FIG. 7  shows an emission spectrum of WE2 (powder sample) on excitation with blue primary radiation (λ exc =460 nm). 
         FIG. 8  shows the excitation spectrum of WE2 based on the emission maximum at 627 nm. 
         FIG. 9  shows a comparison of powder x-ray diffractograms (PXRD) (Mo—Kα 1  radiation) of K 3 WOF 7 :Mn 4+  from experiment and simulation. 
         FIG. 10  shows a PXRD comparison (Mo—K α1  radiation) of K 3 MoOF 7  and K 3 MoOF 7 :Mn 4 +. 
         FIG. 11  shows the thermal characteristics of various luminophores in comparison. 
         FIG. 12  shows a unit cell of the third working example K 2 NaNbO 2 F 4 :Mn 4+  (WE3) of the luminophore (space group No. 225; Fm-3m). 
         FIG. 13  shows an emission spectrum of WE3 (powder sample and single grain) on excitation with blue primary radiation. 
         FIG. 14  shows the excitation spectrum of WE3 based on the emission maximum at 632 nm. 
         FIG. 15  shows a comparison of powder x-ray diffractograms (PXRD) (Mo—Kα 1  radiation) of K 2 NaNbO 2 F 4 :Mn 4+  from experiment and simulation. 
         FIG. 16  shows a PXRD comparison (Mo—K α1  radiation) of K 2 NaNbO 2  F 4  and K 2 NaNbO 2 F 4 :Mn 4+   
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  shows a unit cell with adjoining polyhedra of K 3 MoOF 7 :Mn 4+  along [−100]. K 3 MoOF 7 :Mn 4 +, by comparison with K 2 SiF 6 :Mn 4 +, surprisingly crystallizes in a new, unknown structure type in the P-1 space group (No. 2); the unit cell shows a triclinic metric with lattice parameters a=6.7602(4), b=8.1443(5), c=8.3106(5) Å and α=115.242(2), β=90.582(2), γ=92.732(2)° (volume=413.16(4) Å 3 ). The crystallographic data are summarized in tables 1-3. Mo has partly been replaced by Mn 4+  (not shown). 
       FIG. 1B  shows the unit cell of the crystal structure of K 2 SiF 6 :Mn 4 +, which crystallizes in the cubic space group Fm-3m. The K atoms are shown as unfilled ellipsoids, the F atoms as filled circles, and SiF 6  octahedra with Si in the center and F shaded at the vertices. Si has been partly replaced by Mn (not shown). K 2 SiF 6 :Mn 4+  crystallizes in the K 2 PtCl 6  type in the Fm-3m space group (No. 225). The unit cell shows a cubic metric with a lattice parameter a=8.134(1) Å. 
     A comparison of  FIGS. 1A and 1B  shows that the two structures differ significantly from one another. In cubic K 2 SiF 6 :Mn 4+  there are exclusively SiF 6  octahedra formed from F anions, and in K 3 MoOF 7 :Mn 4+  there are MoOF 5  octahedra formed from O and F anions. By virtue of the arrangement of the O/F atoms, the Mo atom is deflected in each case from the middle of the octahedron in the direction of the O atom (higher covalence of the Mo—O bond than of the Mo—F bond, not shown in the figure). The position and orientation of the respective octahedra in relation to the unit cell are likewise distinctly different from one another in the two structures. 
       FIG. 2  shows an emission spectrum of a powder sample of WE1 on excitation with blue primary radiation (λ exc =460 nm). The x axis shows the wavelength in nanometers, and the y axis the relative intensity in percent. The emission maximum is at 627 nm. 
       FIG. 3  shows the excitation spectrum of WE1 based on the emission maximum at 627 nm. The x axis shows the wavelength in nanometers, and the y axis the relative spectral absorption in percent. 
       FIG. 4  shows a Rietveld refinement of a powder sample of K 3 MoOF 7 :Mn 4 +. The measured curve is represented by the bold curve. The simulation is shown as a light-colored line above the measurement curve. In addition, as well as the difference curve, the reflection positions of K 3 MoOF 7 :Mn 4+  and the KHF 2  present in the luminophore composition are shown. 
       FIG. 5  shows a PXRD comparison (Mo—K α1  radiation) of undoped K 3 MoOF 7  before the ball milling process (intermediate in the synthesis of WE1) with the experimental PXRD of K 3 MoOF 7 :Mn 4 +after the ball milling process. Good agreement is apparent, and so these studies by means of x-ray diffraction show that the structure of K 3 MoOF 7  is conserved by the ball milling process in the case of K 3 MoOF 7 :Mn 4+  too. 
       FIG. 6  shows a unit cell of K 3 WOF 7 :Mn 4+  along [−100]. K 3 WOF 7 :Mn 4+ , by comparison with K 2 SiF 6 :Mn 4 +, surprisingly crystallizes in a new, unknown structure type in the P 21/c space group (No. 14). The unit cell shows monoclinic metric with lattice parameters a=8.8415(4), b=13.7986(6), c=6.7970(3) Å and β=93.0410(10)° (volume=828.07(6) Å 3 ). The crystallographic data are summarized in tables 5 to 7. W has been partly replaced by Mn 4+  (not shown). 
     A comparison of  FIGS. 6 and 1B  shows that the structures of K 3 WOF 7 :Mn 4+  and K 2 SiF 6 :Mn 4+  differ significantly. In cubic K 2 SiF 6 :Mn 4+  there are exclusively SiF 6  octahedra formed from F anions, and in K 3 WOF 7 :Mn there are WOF 5  octahedra formed from O and F anions. The ordering of the O/F atoms (with occupation in each case of half of 2 of the 6 octahedral vertices with O and F), the W atom is deflected in each case from the middle of the octahedron in the direction of the mixedly occupied O/F positions (higher covalence of the W—O bond than of the W—F bond, not shown in the figure). The position and orientation of the respective octahedra in relation to the unit cell are likewise distinctly different from one another in the two structures. 
       FIG. 7  shows an emission spectrum of a powder sample of WE2 on excitation with blue primary radiation (λ exc =460 nm). The emission maximum is at 627 nm. 
       FIG. 8  shows the excitation spectrum of WE2 based on the emission maximum at 627 nm. 
       FIG. 9  shows a comparison of powder x-ray diffractograms (PXRD) (Mo—Kα 1  radiation). What is shown is the x-ray diffractogram measured for the second working example WE2 of the inventive luminophore K 3 WOF 7 :Mn 4+  compared to a simulation based on single-crystal x-ray diffraction data. Good agreement is apparent, and so these studies by means of x-ray powder methods show that the luminophore K 3 WOF 7 :Mn 4+  was preparable in good quality. 
       FIG. 10  shows a PXRD comparison (Mo—K α1  radiation) of undoped K 3 MoOF 7  before the ball milling process (intermediate in the synthesis of WE2) with the experimental PXRD of K 3 WOF 7 :Mn 4+  after the ball milling process. Good agreement is apparent, and so these studies by means of x-ray diffraction show that the structure of K 3 WOF 7  is conserved by the ball milling process in the case of K 3 WOF 7 :Mn 4+  too. 
       FIG. 11  shows the progression of integral intensity I against the temperature of the luminophores K 2 SiF 6 :Mn 4 +, K 3 WOF 7 :Mn 4+  and CaAl 12 O 19 :Mn 4+ . The slow decay time of the Mn 4+  atom, i.e. the slow transition from the excited state to the ground state, which is within the ms range, limits solutions with such luminophores essentially to “low-power” applications (few blue photons/time and area). Otherwise, saturation of the excited state sets in and any further incident blue photon does not trigger a conversion process, such that the overall efficiency of the LED then falls significantly. In such cases, the LED chips, i.e. the semiconductor layer sequences, typically reach temperatures well below 100° C., in view of which a decrease in intensity of only 13% for K 3 WOF 7 :Mn at 75° C. constitutes a surprisingly good value. CaAl 12 O 19 :Mn 4+  shows that the temperature characteristics of oxidic luminophores are much poorer than those of the corresponding fluoridic luminophores. The data for K 2 SiF 6 :Mn 4+  are known from the literature [Temperature dependence of photoluminescence spectra and dynamics of the red-emitting K 2 SiF 6 :Mn 4+  phosphor, Journal of Alloys and Compounds 2017, Shao et al.] 
       FIG. 12  shows a unit cell of K 2 NaNbO 2 F 4 :Mn 4+  along [−100]. K 2 NaNbO 2 F 4 :Mn 4+  crystallizes in the perovskite structure class in the elpasolite structure type (K 2 NaAlF 6 ) like K 2 SiF 6 :Mn 4+  in the Fm-3m space group (No. 225). The unit cell thus also shows cubic metric with lattice parameter a=8.4726(4) Å (volume=608.21 Å 3 ). The crystallographic data are summarized in tables 9 and 10. 
     A comparison of  FIGS. 12 and 1B  shows that the structures of K 2 NaNbO 2 F 4 :Mn 4+  and K 2 SiF 6 :Mn 4+  differ from one another. In cubic K 2 SiF 6 :Mn 4+  there are exclusively SiF 6  octahedra formed from F anions, and in K 2 NaNbO 2 F 4 :Mn 4+  there are NbO 2 F 4  octahedra formed from O and F anions. 
       FIG. 13  shows an emission spectrum of a powder sample and of a single grain of WE3 on excitation with blue primary radiation (λ exc =460 nm powder; (λ exc =448 nm single grain). The emission maximum of the powder sample is at 632 nm, and that of the single grain at 633 nm. 
       FIG. 14  shows the excitation spectrum of WE3 based on the emission maximum at 632 nm. 
       FIG. 15  shows a comparison of powder x-ray diffractograms (PXRD) (Mo—Kα 1  radiation). What is shown is the x-ray diffractogram measured for the third working example WE3 of the inventive luminophore K 2 NaNbO 2 F 4 :Mn 4+  compared to a simulation based on x-ray diffraction data. Good agreement is apparent, and so these studies by means of x-ray powder methods show that the luminophore K 2 NaNbO 2 F 4 :Mn 4+  was preparable in good quality. 
       FIG. 16  shows a PXRD comparison (Mo—K α1  radiation) of undoped K 2 NaNbO 2 F 4  before the ball milling process (intermediate in the synthesis of WE3) with the experimental PXRD of K 2 NaNbO 2 F 4 :Mn 4 +after the ball milling process. Good agreement is apparent, and so these studies by means of x-ray diffraction show that the structure of K 2 NaNbO 2 F 4  is conserved by the ball milling process in the case of K 2 NaNbO 2 F 4 :Mn 4+  too. 
     The working examples described in conjunction with the figures and the features thereof may also be combined with one another in further working examples, even if 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 according to the general part of the description. 
     LIST OF REFERENCE SYMBOLS 
     A spectral absorption 
     WE working example 
     LED light-emitting diode 
     CRI color rendering index 
     LER luminous efficacy of radiation 
     CCT correlated color temperature 
     FWHM spectral width of emission, half-height width 
     ppm parts per million 
     VB comparative example 
     I intensity 
     mol % mole percent 
     nm nanometers 
     ° C. degrees Celsius 
     A exc  excitation wavelength 
     A peak  peak wavelength 
     A max  emission maximum 
     A dom  dominant wavelength