On the structures and luminescence properties of Eu -doped Li CaGeO , Ca GeO , and Ca Ge O compounds.

Powder samples of Li CaGeO , Ca GeO , and Ca Ge O doped by 0.5, 1, 2, 3, 4 and 5 at% Eu relative to the Ca , were prepared using a conventional solid-state synthesis technique. X-ray diffraction (XRD) analyses confirmed obtaining the pure phases at all dopant concentrations. In parallel, single crystals of the three compounds with the experimentally found optimal Eu concentration were grown using a flux method. Structural investigation on the single crystals were done with a special attention to the form of the Ca-O polyhedron, the mean Ca-O distance, the Ca-Ca distance in the structure, the distortion degree of the polyhedron, as well as the Eu-Ca substitution site. The main spectral characteristics were analyzed and several relationships between the structural and spectra features were found. The optimal dopant concentration was 3 at% for Ca GeO and 4at% for Ca Ge O and Li CaGeO . Commission Internationale de l'éclairage coordinates of the samples showed emission colours in the red region close to the standard red coordinates and slightly influenced by the active ion concentration. The obtained results showed that europium-doped Li CaGeO , Ca GeO , and Ca Ge O could be used as red phosphors.