Core/Shell/Shell Nanomaterials of NayF4: Yb, Er/Silica/Polystyrene with High Thermal Stability
International Journal of Nanoparticles and Nanotechnology
Recently, core/shell nanocomposite materials have attracted much interest because the core/shell design enables multimodality imaging, and as well, incorporates designed chemical and biochemical functions    . Rare earth nanoparticles (RENs) with an upconversion property represent a desired class of phosphors in bio-imaging, security and solar applications due to the capability of absorbing red or infrared (IR) radiation and emitting visible photon [4, 5] . The optical property reduces
... al property reduces auto-fluorescence background, avoids photo-bleaching, and facilitates deeper penetration to a biospecimen than conventional down-conversion phosphors    . Another potential application includes anti-counterfeiting because RENs could provide security marks invisible to human eyes, and thus be difficult to mimic    . In addition, RENs could improve solar energy harvesting efficiency by utilizing the IR region of the solar spectrum [12, 13] . Advancing and realizing those applications requires that the Abstract Rare earth based nanomaterials with up conversion properties have attracted much attention because of their potential applications in device and solar energy conversion, as well as in new optical tags in biomedical research. Emission stability has been a concern in realizing these materials' application potential. Towards this goal, new core/shell/shell nanomaterials of NaYF 4 : Yb, Er/silica/polystyrene is synthesized and characterized. Key steps include thermo decomposition method for production of rare earth nanocrystal core, followed with silica shell coated via hydrolysis in reverse micelle solution and, finally, polystyrene outer shell via atom transfer radical polymerization (ATRP). The structures of these nanomaterials are characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray powder diffraction (XRD). Corresponding upconversion spectra and thermal stability are acquired at each stage of the synthesis. Significant improvement in thermal stability upon coating with thin silica shell was found. The NaYF 4 : Yb, Er/silica nanomaterials could be used as is, or functionalized using siloxane chemistry in conjunction with ATRP, as demonstrated in this work. This approach is of generic importance for production of useful rare earth-based nanomaterials, due to the mild reaction conditions used for the surface modification, and the versatility of ATRP to regulate structure and functionality towards designed applications.