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

- The crystal structure of KLa9(GeO4)6O2 and KLa8.37Eu0.63(GeO4)6O2 is reported.
- The electronic structure of the compounds has been resolved using DFT calculations.
- The luminescence properties of KLa8.37Eu0.63(GeO4)6O2 have been studied.

New KLa9(GeO4)6O2 and KLa8.37Eu0.63(GeO4)6O2 germanates with the apatite structure type (space group P63/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 KLa9(GeO4)6O2 is a direct bandgap material, and near-UV excitation leads to the electronic transitions from the O2p- orbitals to the Lad- and K4s- states. Photoluminescence measurements of the Eu3+-doped sample indicate emission in the visible spectral range corresponding to the characteristic transitions from the excited 5D0 and 5D1 levels in europium ion.

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