The Upconversion Luminescence Of Ln³⁺ Doped NaYF₄Nanocrystals

In recent years, upconversion nanoparticles (UCNPs) have attracted great research interest for their extensive biological application, benefiting from low toxicity, good chemical and physical stability, high tissue penetration depth of near-infrared excitation light, and low auto-fluorescence background. However, UCNPs are restricted by the two aspects for their biological application. One the one hand, using a continuous laser of980nm to trigger the UC process would lead to the risk of overheating even may induce cell and tissue damage. On the other hand, luminescent intensity for the UC process is low. Herein we use808nm laser as an exciting resource to address the issue of NIR laser-induced tissue damage. In order to improve the luminescent intensity, we introduce Nd3+ions into the Yb3+ion-sensitized UCNPs as a new NIR absorber and sensitizer, which can be proved to enhance the emission intensity.First,(3-NaYF4:Yb3+/Er3+UCNPs were synthesized by the solvothermal method, and the reaction mechanism was discussed. The effects of reaction parameters on size, phase and luminescent intensity of the UCNPs were also investigated in detail. The UCNPs synthesized by solvothermal method have prominent potentials in biological applications, due to their small size, pure phase and high luminescent intensity.Second, Nd3+/Yb3+/Er3+doped β-NaYF4nanocrystals with different Nd3+concentrations are synthesized, and the luminescence properties of the UCNPs have been studied under808nm excitation for the sensitive biological applications. The NaYF4:20%Yb3+/2%Er3+/0.5%Nd3+UCNPs have the highest emission intensity among all samples under808nm excitation. The UC mechanism under808nm excitation has been discussed in terms of the experimental results. It can be proved that Nd3+ion can absorb the photons effectively and Yb3+ion can play a role of an energy-transfer bridging ion between Nd3+ion and Er3+ion.Finally, we also find that doping with Nd3+ion results in decreasing of reaction temperature on cubic-to-hexagonal phase transition. We can control the phase of UCNPs through doping with Nd3+ion.