“…Other upconversion nanoparticles have also been prepared using the hydrothermal method based on a host of lanthanide fluoride hosts, such as NaYF 4 , − NaYbF 4 , NaLuF 4 , NaGdF 4 , LaF 3 , − BaYF 5 , YF 3 , LuF 3 , CaF 2 , , KMnF 3 (Figure d), KMF 3 (M = Mn, Zn, Cd, or Mg), SrF 2 , and lanthanide oxides or oxysalts, such as Y 2 O 3 , Lu 2 O 3 , TiO 2 , YVO 4 , GdVO 4 , LaPO 4 , and PbWO 4 . It is worth noting that, in the hydrothermal process, the crystalline phase and the morphology of the nanocrystals are affected by many experimental parameters, such as the hydrothermal temperature, reaction time, pH, reactant concentration, solvents, as well as the doping ratio of lanthanide ions …”