Identification Of (Tb,Eu)(9.43)(Sio4)(6)O2-Delta Oxy-Apatite Structures As Nanometric Inclusions In Annealed (Eu,Tb)-Doped Zno/Si Junctions: Combined Electron Diffraction And Chemical Contrast Imaging Studies

(Tb,Eu)-doped ZnO-annealed films at 1100 degrees C showed intense photoluminescense (PL) emission from Eu and Tb ions. The high-temperature annealing led to a chemical segregation and a secondary Zn-free phase formation that is suspected to be responsible for the high PL intensity. Large faceted inclusions of rare-earth (RE) silicates of a size of few hundred nanometers were observed. Owing to various advanced electron microscopy techniques, a detailed microstructural study of these nanometric inclusions combining atomic Z contrast imaging (STEM) and precession electron diffraction tomography (PEDT) data was carried out and resulted in the determination of a hexagonal P6(3)/m-type (Tb,Eu)(9.43)(SiO4)(6)O2-delta structure related to an oxy-apatite structure. Chemical analyses from spectroscopic data (energy-dispersive X-ray mapping and electron energy loss spectroscopy) at the atomic scale showed that both RE elements sitting on two independent (4f) and (6h) atomic sites have three-fold oxidation states, while refinements of their occupancy sites from PEDT data have evidenced preferential deficiency for the first one. The deduced RE-O distances and their corresponding bond valences are listed and discussed with the efficient energy transfer from Tb3+ toward Eu3+.