Mild hydrothermal synthesis, crystal structure, photoluminescence properties and emission quantum yield of a new zirconium germanate with garnet-type structure

The mild hydrothermal synthesis, crystal structure, photoluminescence properties and emission quantum yield of a new sodium zirconium germanate are reported. This material and the method for its preparation represent for the first time a germanium garnet-type material synthesized at autogenous pressure and temperature at 230 °C. The crystal structure was determined by starting from the crystallographic parameters of a common garnet structure and it represents not only a new chemical combination of atoms but also combination of oxidation states in garnet structure. The framework consists of interconnected corner sharing GeO4 tetrahedra and ZrO6 octahedra which form small cavities that accommodate charge compensation Na+ cations. In the course of synthesis the structure can be functionalized by in situ doping with different percentage of Eu3+ ions. This structural flexibility is used to explore the photoluminescent behavior of the active centers embedded in garnet-type host. The materials display the Eu3+5D0→7F0–4 transitions under excitation via intra-4f6 excitation levels and through the O2−→Eu3+ ligand-to-metal charge transfer. A maximum 5D0 quantum efficiency and emission quantum yield values (ca. 0.28 and 0.04±0.01, respectively) were found for the low Eu3+-containing sample, suggesting the presence of concentration quenching effects at higher Eu3+-content (5%).