Spectroscopic study of doped nanoparticles for anti-counterfeiting applications

The work of my thesis is aimed at the optical characterization of crystal nanoparticles doped with rare earth ions for anti-counterfeiting technology. Five compositions of different crystal matrices doped with Nd, Er, Ho and YbEr were studied. The doped matrices were chosen on the basis of their physical and chemical properties like thermal properties and resistance to oxidation and degradation, while the dopants were chosen on the basis of their expected emission properties in the Visible and Near InfraRed (NIR) region such as, a large collection of atom-like emission bands, which cover the whole spectral range from UV to IR with long life times, i.e. from microseconds up to milliseconds. Furthermore, these emissions are extremely stable and produced by peculiar processes, such as upconversion or cross-relaxation. Thanks to these properties it is possible to think of creating a multi-level security code that could be spatially, spectrally and temporally encoded. A thorough spectroscopic analysis is therefore required to assess the potentialities of various compositions to this purpose. For each sample the absorption and emission spectra and the lifetime of the various levels were recorded both in visible and infrared regions. We also studied the stability of the spectroscopic features as a function of the sample around room temperature. The goal is to identify compounds that show intense and stable emissions to be used for a robust anti-counterfeiting technology