Surfactant-tuned phase crystallinity and morphologies of NaYF4:Yb3+,Er3+ hexagonal microstructures and their photoluminescence properties

Typical up-conversion materials of NaYF4:Yb3+,Er3+ microcrystals were synthesized by a hydrothermal route using different surfactants (ethylene diamine tetraacetic acid (EDTA) and citric acid (CA)) as chelating agents. The results and analysis reveal that surfactant as a shape modifier introduced into the reaction system plays an important role in altering the crystalline structures, morphologies, and up-conversion luminescence properties of target crystals. A possible growth mechanism for NaYF4:Yb3+,Er3+ microcrystals to confirm the influence of surfactant on morphology and size was proposed on the basis of the growth rate of different crystal facets and the difference in the type of organic ligand. The luminescence mechanisms for NaYF4:Yb3+,Er3+ microcrystals as well as the correlation between the grain size, defects, morphologies and up-conversion luminescence were thoroughly analyzed.