The long-term study of optical nanoparticles doped with Yb3+/Er3+ and transition metal ions and their real application for imaging and temperature sensing on Triticum aestivum L.

Upconverting nanoparticles (UCNPs) have incredible potential for countless applications, especially in biology and medicine. These NPs can be used to bioimaging animals and plants and analyze their physiology, metabolic pathways, or intercellular interaction in real-time. However, before reaching such an application, we must study the UCNPs physicochemical properties during prolonged storage and their toxicity to a particular species. Herein, SrF2:Yb3+, Er3+ water colloid, additionally doped with transition metals (Sc3+ or Zn2+) to enhance observed emission, were tested during 22 weeks of storage in ambient conditions. The obtained compounds presented high stability throughout the entire duration of the experiment, with minor changes in their composition, emission intensity, and thermal sensitivity. After carefully investigating the phytotoxicity of UCNPs on wheat Triticum aestivum L., we successfully observed UC emission plant imaging under 975 nm excitation while overcoming laser heating that could harm the plant. We were also able to calibrate the UC emission from the UCNPs in the plant to monitor temperature. Moreover, we discover that SrF2:Yb3+, Er3+, Zn2+ can positively influence wheat growth. These results indicate that presented UCNPs are among the most promising candidates for biological and agriculture studies and applications.