On the structures and luminescence properties of Eu³⁺‐doped Li₂CaGeO₄, Ca₂GeO₄, and Ca₅Ge₃O₁₁ compounds

Abstract

Powder samples of Li 2 CaGeO 4 , Ca 2 GeO 4 , and Ca 5 Ge 3 O 11 doped by 0.5, 1, 2, 3, 4 and 5 at% Eu 3+ relative to the Ca 2+ , 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 3+ 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 2 GeO 4 and 4at% for Ca 5 Ge 3 O 11 and Li 2 Ca-GeO 4 . 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 2 CaGeO 4 , Ca 2 GeO 4 , and Ca 5 Ge 3 O 11 could be used as red phosphors.