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. •Up-conversion and thermoluminescence of ultrasmall LaF3:Yb/Er nanocrystals were studied.•XPS spectra have evidenced oxidized Er, La ions within the nanocrystals surface thin layer (1 nm).•Up-conversion luminescence is assigned to the fraction of the Er-ions within the nanocrystals.•Thermoluminescence is related to the trap defects associated with surface states and within the layer.