The purpose of the present study was to reveal the details of the preparation of CaF
2 particles with controllable size (30–900 nm) and shape (spherical, hexagonal, and cubical forms) using a liquid-phase synthesis method, and to demonstrate that a change in the composition of the reactants and crystalline structure of the CaF
2 product could improve material performance. The particles were synthesized from the reaction of CaCl
2 and NH
4F in an aqueous solution in the absence of any additional components (e.g., chemicals, surfactants). Monodispersed particles were achieved by the optimization of the reaction condition parameters: temperature, mixing rate, and reaction time. Control of the particle size was accomplished mainly by changing the concentration of the reactants, which is qualitatively explained by the conventional nucleation theory. Flexibility of the process in controlling particle morphology, from a spherical to a hexagonal and/or a cubical form, was predominantly achieved by varying the concentration of CaCl
2. Since the identical XRD pattern was detected in particles with varying morphologies, the shape transformation was due to changes in particle growth. A theoretical background to support how the particles changed was also added and was compared with an analysis of the number of nuclei. In addition, sufficient adjustment of the reactant compositions made it possible to produce a material with an ultralow refractive index (n
CaF2 was near to n
theoretical CaF2), which was confirmed by the measurement of the refractive index and the material crystallinity.
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