Emission enhancement through Nd-Yb energy transfer in multifunctional NaGdF nanocrystals.

The growing need for biomedical contrast agents has led to the current development of multi-functional materials such as lanthanide-based nanoparticles (NPs). The optical and magnetic properties these nanoparticles (NPs) possess are important to enhance current biomedical imaging techniques. To increase the optical emissions of the nanoparticles, neodymium (Nd) and ytterbium (Yb) were introduced into a magnetic host of NaGdF. The energy transfer between Nd and the Yb was then investigated at multiple concentrations to determine the optimal dopant levels. The NaGdF:Nd,Yb nanoparticles were synthesized through a modified solvothermal method, resulting in rectangular structures, with an average side length of 17.87 ± 4.38 nm. A double dopant concentration of 10% Nd and 4% Yb was found to be optimal, increasing the emission intensity by 71.5% when compared to the widely used Nd single dopant. Decay measurements confirm energy transfer from Nd to Yb, with a lifetime shortening from Nd 1064 nm emission and a calculated lifetime of 12.72 ms with 98% efficiency. Despite NaGdF:Nd,Yb NPs showing a slight decrease in their magnetic response at the expense of optimizing optical emission, as it is directly dependent on the Gd concentration, a strong paramagnetic behavior was still observed. These results corroborate that NaGdF:Nd,Yb NPs are viable candidates for multimodal imaging.