Thin films of ErNbO₄ and YbNbO₄ prepared by sol–gel

RENbO₄ (RE = Er or Yb) is the most common secondary phase when Er³⁺/Yb³⁺ co-doped LiNbO₃ is prepared. Thin films of ErNbO₄ and YbNbO₄ were prepared by spin coating on sapphire (0001) substrates in order to characterize these phases in the form of oriented layers. Coating solution was prepared by sol–gel method from metal alkoxides. The annealing of the films was performed at 800 or 1000 °C in air or oxygen. Prepared films were characterized by XRD, photoluminescence measurement and SEM imaging. The prepared samples contained mostly monoclinic RENbO₄ with a small fraction of tetragonal RENbO₄. Higher annealing temperature and oxygen atmosphere were shown beneficial for the crystallinity of the films. The results may be helpful at the analysis of Er,Yb:LiNbO₃ thin films where these phases can appear when the solid state solubility of Er³⁺ and Yb³⁺ cations is exceeded.

The micrographs of prepared films show a great difference in surface morphology.