The influence of the nanocrystals size and surface on the Yb/Er doped LaF3 luminescence properties

Up-conversion luminescence and thermoluminescence properties of LaF3 nanocrystals, with sizes of about 20 nm, were studied and discussed in relation to -size and surface related effects. XPS spectra have evidenced the presence of oxidized Er and La ions within a thin layer (of about 1 nm thickness) at the nanocrystals surface, as well as Yb ions bonded with fluorine ions. The green ((2H11/2, 4S3/2) → 4I15/2) and red (4F9/2 → 4I15/2) up-conversion emissions of Er3+ ions are influenced by the relative dominance of Er-ions that reside within the thin oxidized layer. The broad thermoluminescence curves are assigned to the recombination of trap defects associated with surface states and within the oxidized surface layer.