One Ion, Many Facets: Efficient, Structurally and Thermally Sensitive Luminescence of Eu2+ in Binary and Ternary Strontium Borohydride Chlorides

The Eu2+-doped mixed alkaline metal strontium borohydride chlorides ASr(BH4)3–xClx (A = K, Rb, Cs) and Eu2+-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 Eu2+ doped phosphor so far. Additionally, bright luminescence, high quantum efficiencies, and very low thermal quenching of these Eu2+-doped borohydrides show that such host materials could serve in solid state lighting applications.
This project has received funding from the European Union's Horizon 2020 FET Open programme under grant agreement No 801305 (NanoTBTech).