Variation of the Eu(II) emission wavelength by substitution of fluoride by hydride in fluorite-type compounds EuH(x)F(2-x) (0.20 ≤ x ≤ 0.67).

Mixed-hydride fluorides EuHxF2-x were prepared by the solid-state reaction of EuF2 and EuH2 under hydrogen gas pressure in an autoclave. Eu(II) luminescence is observed for 0.20 ≤ x ≤ 0.67, while pure EuF2 does not show any emission. The energy of the emission depends strongly on the degree of substitution x. For low hydride contents, yellow emission is observed, whereas higher hydride contents lead to red emission. The red shift is attributed to the nephelauxetic effect of the hydride anion. Remarkably, limited concentration quenching is observed in EuHxF2-x (0.20 ≤ x ≤ 0.67). This observation is explained by suppression of long-range energy migration due to disorder in the local environment of Eu(2+) in the mixed H/F crystals. The strong x dependence of the luminescence maxima proves hydride-fluoride substitution to be a valuable tool to tune the emission wavelength of Eu(II)-containing phosphors.