The early synthetic procedure was developed by van Veggel and co-workers, who prepared sub-10 nm LaF3:Ln (Ln = Eu, Er, Nd, Ho) NPs through the coprecipitation of RE3+ and F− ions assisted by ammonium di-n-octadecyldithiophosphate in ethanol−water solution at a low temperature of 75 °C.10,209 In their studies, ammonium di-n-octadecyldithiophosphate was used as capping ligand to control particle growth, stabilize the NPs against aggregation, and give the NPs solubility in organic solution.
Using a similar procedure, YVO4 NPs (5−10 nm) could be made by replacing F− with VO43− ions.390 The approach was expanded and refined by Yi and Chow, who synthesized LaF3:Yb,Ln (Ln = Er, Tm, Ho) UC NPs with a smaller particle size of 5.4 nm and a narrow size distribution of ±0.9 nm.80 Later, van Veggel and co-workers presented a series of waterdispersible LnF3 (Ln = La, Ce, Nd, Eu, Gd) and NaxLnyFz (Ln = Gd, Dy−Er, Yb) NPs (3−10 nm) by precipitating corresponding ions from their aqueous solution with the aidof NH4OH-neutralized citric acid at 75 °C.391−396 In this system, citrate turned out to be a suitable stabilizing ligand, which can cap on the surface of the NPs and make them soluble in water. |
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