Luminescence Properties of α‑NaYF₄:Nd³⁺ Nanocrystals Dispersed in Liquid: Local Field Effect Investigation

Pure α-NaYF₄:Nd³⁺ nanocrystals of various sizes from 6 to 18 nm were successfully synthesized by a solvothermal method. By controlling the doping concentration of Nd³⁺ ions, α-NaYF₄ nanocrystals with different quantum efficiencies were prepared. The monodispersed oleate-capped nanocrystals were dispersed in several nonpolar solvents to obtain stable colloids. Under the excitation by an 803 nm laser, luminescent decay curves of the colloids were measured. The relationship between the emission lifetimes of samples and the effective refractive indices of solvents was studied. The local field correction factor for the samples of 18 nm with different quantum efficiencies is expressed by the real cavity model which indicates the local field effect is independent of the emission quantum efficiency. When the particle size decreases to 6 nm, the preferred model alters from the real cavity model to the virtual cavity model which might be derived from changing of polarizability density.