Synthesis of Colloidal Upconverting NaYF₄ Nanocrystals Doped with Er³⁺, Yb³⁺ and Tm³⁺, Yb³⁺ via Thermal Decomposition of Lanthanide Trifluoroacetate Precursors

Abstract

Upconverting lanthanide-doped nanocrystals were synthesized via the thermal decomposition of trifluoroacetate precursors in a mixture of oleic acid and octadecene. This method provides highly luminescent nanoparticles through a simple one-pot technique with only one preparatory step. The Er3+, Yb3+ and Tm3+, Yb3+ doped cubic NaYF4 nanocrystals are colloidally stable in nonpolar organic solvents and exhibit green/red and blue upconversion luminescence, respectively, under 977 nm laser excitation with low power densities.

Synthesis of β-Phase NaYF4:Yb,Er Upconversion Nanocrystals and Nanorods by Hot-Injection of Small Particles of the α-Phase

“…During the last years, a large number of research papers was pub-lished on the synthesis of NaREF 4 nanocrystals (RE = rare-earth), since NaREF 4 and LiREF 4 are attractive host lattices for a variety of functional optical materials such as upconversion phosphors, [6][7][8][9][10][11][12][13][14] quantum-cutting phosphors, [15][16][17][18][19] laser materials, [20,21] and materials for solar cell applications [22][23][24][25][26]. A variety of synthetic methods has been described for producing solvent-dispersible sodium rare-earth tetrafluoride nanocrystals with controlled size, shape and capping ligand, including thermal decomposition, [7,[27][28][29][30][31][32] co-precipitation, [6,11,[33][34][35][36][37][38][39][40] or solvothermal methods [41][42][43][44][45][46][47]…”

“…Nearly monodisperse -NaREF 4 nanocrystals are often synthesized by the thermal decomposition of the metal trifluoroacetates in hot solvent mixtures containing oleic acid [7,[27][28][29][30][31][32]. It has been reported, however, that even in this case very small NaYF 4 :Yb,Er nanocrystals of the cubic -phase are formed as intermediate and that the final -NaYF 4 :Yb,Er nanocrystals with the hexagonal phase grow from these particles at elevated temperatures [27].…”

Recent advances in the optimization and functionalization of upconversion nanomaterials for in vivo bioapplications

“…This method is now considered the standard method for obtaining upconversion nanocrystals. [17][18][19][20][21][22] Therefore, most advances made in recent years are based on these upconversion NaREF 4 nanocrystals.…”

“…Because the majority of high-efficiency and uniform UCNPs are synthesized in organic solvents by the thermal decomposition method or the modified solvothermal method, the surfaces of these UCNPs are capped by hydrophobic organic ligands that hinder the dispersion of UCNPs in biocompatible aqueous solutions. [17][18][19][20] To date, various methods have been developed to modify the surface of UCNPs and are summarized in the published reviews. 3 Almost all types of functional bioimaging applications employing UCNPs use surface modification methods to introduce the required surface ligands to improve biocompatibility.…”

“…Our group reported an 18 F labeling method to integrate PET imaging ability into UCNPs. 57 Because of the strong interaction between F and rare earth elements, 18 F À cations were easily bonded to the surface of UCNPs by simply mixing the solution containing 18 F À and UCNPs. After the 18 F À labeled UCNPs were injected into the paw of a mouse, the PET imaging signal could be detected in the lymph node.…”