EXAFS studies on erbium-doped TiO2 and ZrO2 sol-gel thin films

High concentration Er-doped TiO2 and ZrO2 sol-gel layers, annealed under an O flow at 300 and 650 C, resp., were studied at the Er LIII edge (8358 eV) by XANES and EXAFS to obtain information about the local atomic arrangement around the incorporated rare earths. TEM experiments were also carried out in order to support XAS studies by a knowledge of the global structure of the sol-gel layer. Analysis of the XAS data reveals that, in the case of annealing treatment at 300 C, the local atomic structure surrounding the Er ion appears amorphous for both samples, while after an annealing treatment at 650 C, a crystalline structure around the dopant is dependent on the nature of the lattice cation (Ti or Zr). For such an annealing temperature, the local atomic environment around the Er ion appears to be amorphous in the case of an anatase matrix while it seems to have crystallized around the dopant in the case of ZrO2. For both these compounds, XAS data reveal that a pairing effect between the Er ions probably occurs. TEM studies on the samples annealed at 650 C show the appearance of other phases different from the matrix. For both compounds, analysis of these sets of data reveals that the Er ion has not formed metallic Er in the matrix. For the Er-doped TiO2 sol-gel layers, it can be concluded that the rare earth has not precipitated in the form of Er oxide clusters. For the Er-doped ZrO2 sol-gel layers, nothing can be deduced about the possible appearance of Er2O3. The appearance of another phase, with the formula near Zr3Er4O12, likely occurs in the case of the Er-doped ZrO2 sol-gel layer annealed at 650 C, while a solid solution of ErxTiyOz formed in the case of the Er-doped TiO2 sol-gel layer (annealed at 650 C). 33 refs.