Lumineszenz von Mn4+-substituierten Fluoridometallaten(IV) und Untersuchungen zur Chemie mit Brom(III)-fluorid

A white LED (light emitting diode) can be built by a combination of a LED chip with a phosphor, which then emits light when excited by the emission of the chip. So far the emitted spectra shows a relative small intensity in the red light region and additional red phosphors show a maximum of luminescence significantly above the maximum of the red light sensitivity of the human eye. This is why new partially Mn4+-substituted compounds were synthesized in this work. These are Li2MF6:Mn (M = Si, Ge, Ti, Sn, Pb), A2PbF6:Mn (A = Na, K, Rb, Cs), MgGeF6:Mn, MgPbF6:Mn, CaMF6:Mn (M = Ge, Sn, Pb, Zr, Hf), SrSnF6:Mn, SrTiF6:Mn, BaPbF6:Mn, ZnMF6:Mn (M = Sn, Pb, Zr, Hf), and CdMF6:Mn (M = Pb, Hf) which all show a red emission under UV-irradiation. Due to this red luminescence these Mn4+-containing compounds can be potentially used as red phosphors in white light emitting diodes (LEDs). In comparison to the common synthesis route, these red phosphors were synthesized via direct fluorination, which avoids the use of hydrofluoric acid. A second advantage is that the concentration of the Mn4+ ions can be regulated easily by varying the mass of the initial compounds. The most blue shifted emission maxima are shown for SrSnF6:Mn, CdHfF6:Mn, and Na2PbF6:Mn with 627 nm, which is shifted circa 4 nm hypsochromic compared with the maximum of the commercially used K2SiF6:Mn. The sensitivity of the human eye towards red light decreases rapidly with increasing wavelength, which is why even this small shift in the emission maximum yields to a significant increase of the perceived red color. Considering only this, these three compounds are favorable red phosphors for white LEDs. Dome host structures, in which some Mn4+ ions should be inserted, were also synthesized. Thereby the crystal structures of the compounds MgHfF6, CdHfF6, CdZrF6, CaPbF6, CaZrF6, and CaHfF6 were determined by powder X-ray diffraction in the NaSbF6 structure type. The crystal structure of SrPbF6 was corrected to crystallize in the space group P42/mcm (Nr. 132), which now corresponds in significantly smaller Pb–F distances, which are comparable with other hexafluorido metallates(IV). Furthermore the crystal structures of the alkali hexafluorido metallates(IV) were determined by powder X-ray diffraction data and also some Pb4+ ions were substituted by Mn4+ ions. Li2PbF6 crystallizes in the PbSb2O6 structure type, Na2PbF6 in the trirutile type, and K2PbF6, Rb2PbF6, and Cs2PbF6 in the K2GeF6 type. Contributions to the crystal structure determination of β-MnF4, K3MnF6, Pb3F8, A2SiF6 (A = Rb, Cs, Tl), Tl3SiF7, KLiSiF6, and CsLiSiF6 were made by performing additional analyses and synthesis of starting materials. The crystal structure of K3MnF6 contains both elongated and compressed Jahn-Teller distorted octahedra, which were not reported inside the same compound. The compounds A2SiF6 (A = Rb, Cs, Tl) crystallize in the K2PtCl6 structure type and Tl3SiF7 was corrected to crystallize in the space group P63mc. In the previously known structure, partially occupied fluorine atoms were present, which can be avoided by the new description. Additionally a second modification of Tl3SiF7 was obtained in the (NH4)3[SiF6]F structure type. The Si4+ ions in the mineral Knasibfite are also octahedrally coordinated by fluorine atoms, as it is in K2SiF6:Mn. It was possible to synthesize the mineral Knasibfite K3Na4[SiF6]3[BF4] for the first time and the crystal structure was determined. The compound turns out to show dimorphism. K3Na4[GeF6]3[BF4] was also prepared, which is also dimorph and isotypic to Knasibfite. Trying to substitute some Si4+ ions with Mn4+ ions does not results in a compound which shows luminescence by UV irradiation. To perform the substitution of M4+ ions by Mn4+ ions some proper manganese compounds are needed. Therefore "Manganese(III) acetate dihydrate" was synthesized and treated with acetic anhydride. The obtained crystals show a crystal structure with huge molecular wheels, which consist of 18 Mn atoms, linked by acetic acid anions. Other potentially applicable manganese compounds are the binary manganese fluorides, which were also synthesized. The crystal structure of MnF3 was corrected and can be described now with an even smaller unit cell and less symmetry independent atoms. Additionally to the crystal structure data, vibration spectra were contributed to the characterization of β-MnF4, for which MnF4 was synthesized. Furthermore the crystal structures of the mixed valence binary fluorides Mn2F5 and Mn3F8 could be determined. Mn2F5 crystallizes in the CaCrF5 structure type whereas Mn3F8 crystallize in a novel structure type. In a second subject the reactions of metals or metal halides with BrF3 were examined. This resulted in crystals of the compounds [BrF2][MF6] (M = Nb, Ta) and [BrF2]2[SnF6], which contain the fluoridobrom(III) cation. These compounds crystallize istotypic to [BrF2][SbF6] or [BrF2]2[GeF6], respectively. Compounds containing a fluoridobromate(III) anion could also be obtained by the reaction of metals or metal halides with BrF3. These were Ag[BrF4], of which the crystal structure is isotypic to K[BrF4], PbF[Br2F7] which is the first fluoridobromate(III) anion containing a p-block element and Ba2[Br3F10]2[Br4F14]2. The crystal structure of the last named compound contains two isomeric [Br4F13]− anions which were previously only quantum chemically calculated but no compound containing them was reported in the past. The reaction of PbF2 with BrF3 made a contribution to the crystal structure determination of Pb3F8. The bulk compositions of the received samples were analyzed by powder X-ray diffraction and IR spectroscopy. Through acid base reactions in BrF3 the compounds Ba[NbF6]2, Ag2SnF6, Ag2TiF6•BrF3, Ag2GeF6•BrF3, Ag4[Ti3F16], AgNbF6, and AgTaF6 were obtained as twinned crystals, except of Ba[NbF6]2. From all these compounds the crystal structures could be determined using X-ray diffraction data. Ba[NbF6]2 crystallizes in the cubic crystal system and the lattice parameter was determined to a = 9.9164(5) Å (V = 975.1 ų), but no plausible structure model could be predicted. Ag2SnF6 crystallizes isotypic to Cd2Fe(CN)6 (if the CN− ions are considered as one atom) in the space group P3 ̅ (Nr. 147). Both Ag2TiF6•BrF3 and Ag2GeF6•BrF3 crystallize in the monoclinic crystal system. Due to the low quality of the crystals, the space group could not be determined reliably, which is why it is not safe if both crystallize isotypic. Ag4[Ti3F16] contains the unknown molecular [Ti3F16]4− anion. The [TiF6] building units are connected via the fluorine atoms which are cis arranged to each other. AgNbF6 and AgTaF6 crystallize isotypic in the space group Pbcn (Nr. 60) at 100 K and show a group-subgroup relation to the room temperature modification. The volume of the room temperature modification is four times smaller than those of the low temperature modification. To analyze the purity of the obtained samples all samples were characterized by powder X-ray diffraction and IR spectroscopy.