Nanocomposite electrospun fibers containing upconverting Nanoparticles

Abstract

Upconverting nanoparticles (UCNPs) which present outstanding optical properties can offer new possibilities in fluorescent applications. In comparison with other fluorescence materials like semiconductors and organic fluorophores, they show many advantages such as high photostability, low toxicity and weak background autofluorescence. They also exhibit characteristic properties like large shift between the fluorescent emission signal and the infrared excitation wavelength, multi-and narrow-band absorption and emission in visible and near infrared (Vis/NIR) which are very important for applications like imaging and sensing. The upconversion luminescence emission or the quenching characteristics of UCNPs can be changed if they are exposed to physical or chemical environmental factors something that is very useful for biomedical applications like biosensing. Furthermore, their functionalization with specific dyes can alter the range of luminescence response and serve as ratiometric sensors to pH and to various gases like ammonia, CO2, CO, NO2. Flexible PMMA, PEO/PMMA and PEO/PMMA/RB fibers containing the upconverting nanoparticles (UCNPs) of lanthanide-doped sodium yttrium fluoride have been successfully fabricated by electrospinning. Electrospun nano- and microfibers which offer large surface area can increase the performance of UCNPs by maintaining their fluorescence efficiency and enhancing their overall sensibility because of the larger surface area. The electrospun fibers with the embedded UCNPs were morphologically and optically characterized. Morphological studies for the examination of the uniformity and aggregation effects of the UCNP encapsulation within the fibers have been conducted, followed by upconversion emission characterization by pulsed near-infrared excitation. The results indicated that upconversion properties of the UCNPs are largely preserved in the fibrous mats. Upconversion nanocomposites with controlled morphologies, properties and structures could be very useful in a wide range of applications. Research and optimization of such nanocomposite fibrous systems could promote the development of efficient upconverting electrospun fiber mats which could be used in sensing applications as gas and pH sensors.