Optically active uniform potassium and lithium rare earth fluoride nanocrystals derived from metal trifluroacetate precursors

This paper reports the first systematical synthesis of near-monodisperse potassium and lithium rare earth (RE) fluoride (K(Li)REF₄) nanocrystals with diverse shapes (cubic KLaF₄ and KCeF₄ wormlike nanowires, nanocubes and nanopolyhedra; cubic LiREF₄ (RE = Pr to Gd, Y) nanopolyhedra; tetragonal LiREF₄ (RE = Tb to Lu, Y) rhombic nanoplates) via co-thermolysis of Li(CF₃COO) or K(CF₃COO) and RE(CF₃COO)₃ in a hot oleic acid/oleylamine/1-octadecene solution. The effects of the solvent composition, reaction temperature and time on the crystal phase purity, shape, and size of the as-prepared nanocrystals have been investigated in detail. The formation of monodisperse nanocrystals is found to strongly depend upon the nature of both alkali metals from Li to K, and the rare earth series from La to Lu and Y. Based on the series of experimental results, a controlled-growth mechanism has also been proposed. In addition, the ease of doping of these as-synthesized host nanocrystals for designed luminescence properties is assessed. For example, monodisperse and single-crystalline Eu³⁺ doped KGdF₄, Yb³⁺ and Er³⁺ co-doped LiYF₄ nanocrystals redispersed in cyclohexane exhibit visible room-temperature red and green emissions under ultraviolet (UV) excitation and near infrared (NIR) 980 nm laser excitation, respectively.