AbstractPure α‐NaYF4: Nd3+ nanocrystals of various sizes from 6 nm to 18 nm were successfully synthesized by a solvothermal method. The monodispersed oleate‐capped nanocrystals were dispersed in several nonpolar solvents to obtain stable colloidal. Under the excitation by an 803 nm laser, luminescent decay curves of the colloidal were measured. The relationship between emission lifetimes of samples and effective refractive indices of solvents was studied for the local field correction factor. In the 18 nm sample, the real cavity model was preferable model. As the particle size decreased to 6 nm, the preferred model altered from the real cavity model to the virtual cavity model which might be derived from changing of polarizability density. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)