The Eu 2+ -doped mixed alkaline metal strontium borohydride chlorides ASr(BH4)3-xClx (A = K, Rb, Cs) and Eu 2+ -doped strontium borohydride chloride Sr(BH4)2-xClx have been prepared by mechanochemical synthesis. Intense blue photoluminescence for Sr(BH4)2-xClx (λem= 457 nm) and cyan photoluminescence for the perovskite-type mixed alkaline metal strontium borohydride chlorides ASr(BH4)3-xClx (A = K, Rb, Cs) (λem = 490 nm) is already observable after short milling times. Temperature dependent luminescence measurements reveal an appreciable blue shift with increasing temperature for all ASr(BH4)3-xClx (A = K, Rb, Cs) until 500 K. This extremely large shift, caused by structural relaxation, as well as the vibrationally induced emission band broadening can serve as a sensitive response signal for temperature sensing, and this unique behavior has, to the best of our knowledge, not been reported in any Eu 2+ doped phosphor so far. Additionally, bright luminescence, high quantum efficiencies, and very low thermal quenching of these Eu 2+ -doped borohydrides show that such host materials could serve in solid state lighting applications. xClx:Eu 2+ (A = K, Rb, Cs) for the first time. All discussed ternary compounds show efficient cyan emission at room temperature as well as a strongly temperature-dependent shift of the emission energies. This unusually strong response of the luminescence properties of Eu 2+ with Chemistry of Materials 2019, 31, 8957-8968 https://doi.org/10.1021/acs.chemmater.9b03048regard to temperature changes may be interesting for potential applications in the field of thermometry. Experimental sectionSynthesis. Due to moisture and air sensitivity all compounds were handled in an argon-filled glove box. The mixed metal borohydrides ASr(BH4)3-xClx:Eu 2+ (A = K, Rb, Cs) were prepared via mechanochemical reaction of LiBH4 (Alfa Aesar, 95%), SrCl2 (Alfa Aesar, 99.995%), the corresponding alkaline borohydrides (KBH4, Alfa Aesar 98%; RbBH4 and CsBH4 prepared from Rb or Cs metal and NaBH4 in ethanol according to the procedure described in Ref 34) as well as EuH2 (2 mol% doping; synthesized via hydrogenation of europium metal in an autoclave made from hydrogen-resistant Böhler L718 alloy) in a Fritsch Pulverisette Premium Line 7 in a ZrO2 bowl with an overpressure valve. Sr(BH4)2-xClx:Eu 2+ was prepared via mechanochemical reaction of stoichiometric amounts of SrCl2, LiBH4 and 2 mol% EuH2. 10 ZrO2 balls with a diameter of 10 mm are used together with approximately 0.3 g of reactants. Caution! Overpressure may build up during milling via decomposition of the borohydrides. Reactants were milled during 19 cycles with 2 minutes of milling at 600 rpm followed by 3 minutes pauses to prevent heating of the samples. To increase crystallinity, the samples were annealed at 200 °C in fused silica ampoules for 2 days. Powder x-ray diffraction (XRD). For powder XRD analysis, a STOE STADI P diffractometer (Cu-Kα1 radiation, λ = 1.54051 Å (determined from a silicon standard)), Ge-(111)monochromator) including a DECTRIS Mythen...

The unprecedented borate hydride Sr5(BO3)3H and deuteride Sr5(11BO3)3D crystallizing in an apatite‐related structure are reported. Despite the presence of hydride anions, the compound decomposes only slowly in air. Doped with Eu2+, it shows broad‐band orange‐red emission under violet excitation owing to the 4f65d–4f7 transition of Eu2+. The observed 1H NMR chemical shift is in good agreement with previously reported 1H chemical shifts of ionic metal hydrides as well as with quantum chemical calculations and very different from 1H chemical shifts usually found for hydroxide ions in similar materials. FTIR and Raman spectroscopy of different samples containing 1H, 2H, natB, and 11B combined with calculations unambiguously prove the absence of hydroxide ions and the sole incorporation of hydride ions into the borate. The orange‐red emission obtained by doping with Eu2+ shows that the new compound class might be a promising host material for optical applications.