The present invention relates to a method of preparing lanthanide-doped NaYF4 nanocrystals, the method comprising: (A) providing a first solution comprising a non-coordinating solvent, a fatty acid coordinating ligand, sodium trifluoroacetate, yttrium trifluoroacetate, a first doping lanthanide trifluoroacetate and a second doping lanthanide trifluoroacetate, and a second solution comprising the non-coordinating solvent and the fatty acid coordinating ligand, the first and second solutions being substantially free of water and oxygen; (B) in an inert atmosphere, slowly adding the first solution heated at a temperature between about 100° C. and about 150° C. to the second solution heated at temperature between about 290° C. and about 330° C., thereby producing a reaction mixture containing the nanocrystals; and (C) recovering the nanocrystals from the reaction mixture. The invention also relates to lanthanide-doped uniformly shaped cubic NaYF4 nanocrystals having an average particle size of at most about 50 nm with a standard deviation of at most about 15%. Finally, the invention also relates to methods of (A) identifying or authenticating a product, (B) labelling an analyte, (C) detecting an analyte, and (D) producing a light source for the telecommunication industry using the above nanocrystals.