Executive Summary : | Bio-imaging based on ionizing radiation is to detect high energy emissions from radioactive elements or the passage of X-rays through the human body. The micron sized particles cannot be used for bio-photonic applications as micron sized particles may cause blockage in biological systems. Therefore, it is required to develop nanophosphors with absorbance or excitation/emission maxima falling in the region where the absorbance/auto fluorescence of tissues is minimal i.e., between 650 and 1450 nm, an “imaging window”. It suitable for deep penetration of light. Generally, an ideal fluorescent probe must be resistant to photobleaching, ultrasensitive, biocompatible and nontoxic. Furthermore, it must have high fluorescent efficiency and superior chemical and physical stability. Among various inorganic hosts, fluorides have been evolved as good hosts for up-conversion nanophosphors (UCNPs) due to their low phonon energy which is required for high radiative transition rate and high chemical stability. Surface modification is required for such UCNPs to obtain biocompatibility by using different organic polymer surfactant, for example polyethylenimine (PEI), polyethylene glycol (PEG) and polyacrylic acid (PAA). This is also essential for making these nanophosphors water soluble and to control the growth of nanophosphors. Thus, the UCNPs are considered as an alternative to the traditional bio-labels and can be utilized in labelling, imaging and other bio-photonic applications. Current studies on UCNPs suggest their applicability in vitro-based optical imaging. However, these nanophosphors need to be studied in deeper details for its wide applicability in animal models. Further, there is also a greater scope to develop biocompatible, multifunctional up-conversion nanophosphors with high photoluminescence ability, strong super paramagnetic properties and easy bio-conjugation for magnetic separation purposes in wide range of applications. In the present project, the main aim is to consider novel oxide/fluoride based lattices due to their low phonon energies with less non-radiative decay rates to the doped RE ion fluorescent levels. This helps in observing the up-conversion process easily and more efficiently. The basic idea of using NIR is to excite the host system to get luminescence in visible range. By taking into account the problems of the conventional bio-imaging methods, the method of up-conversion presents itself as a better alternative with no side effects on the biological samples, bio-imaging and targeted drug delivery. |