Investigation of Upconversion Luminescence Attenuation in Aqueous Solutions Under 980 nm and 808 nm Irradiation

Lanthanide ions-doped upconversion nanoparticles (UCNPs) have shown great potential in various biomedical applications. However, the upconversion luminescence (UCL) intensity of UCNPs in water environment tends to be quenched. This quenching is typically attributed to non-radiative relaxation of the excited state. In this study, we designed a core–shell–shell–shell NaYb0.88 Er0.12F4@NaY0.9b0.1F4@NaY0.6Nd0.3Yb0.1F4@NaYF4 UCNPs that could be excited by both 980 nm and 808 nm laser, due to the doping of Nd3+ and Yb3+ ions. Our research not only utilized bulk spectral measurement but also employed single-particle level microscopic imaging to comprehensively investigate the impact of water molecules on UCL under 980 nm and 808 nm irradiation. Interestingly, our findings indicate that the absorption of water molecules has a significant effect on the UCL decay of UCNPs in aqueous solutions when excited by a 980 nm laser. This work offers a new perspective on the luminescence behavior of UCNPs in aquatic environments and provides valuable insights for their application and development in biomedicine.