| Abstract [eng] |
Lanthanide-doped upconverting nanoparticles are the new kind of nanoparticles that utilizes nonlinear optical process called upconversion and have potencial to be used as biomarkers in bioimaging. These nanoparticles have a few features that gives them advantage over other nanoparticles such as quantum dots. During upconversion process multiple low energy excitation photons are converted to the higher energy emission. For excitation NIR (near-infrared) is ussually used. Since various biological tissues have optical transparency window in NIR spectrum it makes these particles great for bioimaging. Using NIR not only gives better light penetration of biological tissues, but also allows to avoid various photodamage effects that can be caused by the higher energy radiation such as UV. In case of upconverting nanoparticles there are less worries about toxicity than there are in other particles such as quantum dots, which contains various toxic elements, in example: cadmium [1]. In order to overcome the limitations of the application of the nanoparticles its surface quenching effects must be understood better. There are not a lot of scientific works that investigate enviroment quenching effects of the upconverting nanoparticles. Water is universally reconized as the very good quencher and is pretty important , because nanoparticles have to be rendered dispersable in it before it can be used in biological systems. Most of the scientific works, which investigate solvent quenching effects on the nanoparticles mostly investigate the effect of water and usually do not pay a lot of attention to the quenching effects of the other, organic solvents. In this work we investigated enviroment quenching of the nanoparticles. To this end we measured decay profiles of the NaGdF4: Yb3+, Er3+ upconverting nanoparticles. Decay profiles of the nanoparticles were measured using time correliated single photon counting method. For the excitation IR 980 nm laser was used. After measurements decay profiles were fitted with exponential function and then excitation lifetimes of the nanoparticles were obtained. We investigated how decay profiles and excitation lifetimes differs in different solvents: water and toluene, and how it depends on different coatings of the nanoparticles. We also checked how NaGdF4 inert shells affects decay profiles and excitation lifetimes in different solvents. Obtained results: decay profiles and excitation lifetimes were compared and exponential behavior of the decay profiles were disscused. |
