Alkaline-Earth Metal Hydrides as Novel Host Lattices for EuII Luminescence

Luminescence of divalent europium has been investigated for the first time in metal hydrides. A complete solid-solution series was found for the pseudobinary system Eu x Sr1–x H2 [a = 637.6(1) pm −12.1(3)x pm, b = 387.0(1)–6.5(2)x pm, c = 732.2(2)–10.1(4)x pm]. Europium-doped alkaline-earth hydrides Eu x M1–x H2 (M = Ca, Sr, Ba) with a small europium concentration (x = 0.005) exhibit luminescence with maximum emission wavelengths of 764 nm (M = Ca), 728 nm (M = Sr), and 750 nm (M = Ba); i.e., the emission energy of divalent europium shows an extremely large red shift compared to the emission energies of fluorides or oxides. Theoretical calculations (LDA+U) confirm decreasing band gaps with increasing europium content of the solid solutions.