Structure and optical properties of KLa9(GeO4)6O2 and KLa8.37Eu0.63(GeO4)6O2

New KLa 9 (GeO 4 ) 6 O 2 and KLa 8.37 Eu 0.63 (GeO 4 ) 6 O 2 germanates with the apatite structure type (space group P 6 3 /m , Z = 1) have been synthesized by the sol-gel method using ethylenediaminetetraacetic acid as a precursor and characterized by powder X-ray diffraction, scanning electron microscopy and diffuse reflectance spectroscopy. Density functional theory calculations reveal that KLa 9 (GeO 4 ) 6 O 2 is a direct bandgap material, and near-UV excitation leads to the electronic transitions from the O 2p - orbitals to the La d - and K 4s - states. Photoluminescence measurements of the Eu 3+ -doped sample indicate emission in the visible spectral range corresponding to the characteristic transitions from the excited 5 D 0 and 5 D 1 levels in europium ion.