Controlled synthesis, multicolor luminescence, and optical thermometer of bifunctional NaYbF4:Nd3+@NaYF4:Yb3+ active-core/active-shell colloidal nanoparticles

The novel NaYbF4:Nd3+@NaYF4:Yb3+ active-core/active-shell colloidal nanoparticles (NPs) were synthesized, and their structures were studied by the XRD, TEM, and HRTEM techniques. Compared with NaYbF4:Nd3+ active-core NPs, the maximum 45-fold enhancement of total emission intensity is obtained in the active-core/active-shell NPs. The tunable green-white-yellow multicolor emissions are realized by tuning the Yb3+ concentration in NaYF4:Yb3+ active-shell. By using the fluorescence intensity ratio technology, the 4G9/2 and 4G7/2 levels of Nd3+ in NaYbF4:Nd3+ active-core is verified as thermally coupled levels. Based on the change of the intensity ratio of 523 nm-543 nm with temperature, a better behavior as a temperature sensor has been obtained with a maximum sensitivity of 0.0018 K−1 at 400 K. The resulting active-core/active-shell NPs show bifunctional property and have potential application in fluorescent and temperature nano-probes.