Spectral Modulation of Upconversion Emissions with Composition Tuning and Surface Plasmonic Resonance

Rare-earth doped upconversion nanocrystals (UCNCs) have lately drawn much attention in different fields such as solar cells, biolabeling and display technologies due to their unique ability to convert lower energy photons into high energy photons and the associated advantages. For example, with an IR excitation, UCNCs can function as effective biolabels with very large sample penetration depth, high photostability and highsignal-to-noise ratio. The ability to achieve this shorter wavelength emission through an upconversion process is of significance for activating certain chemical or biological processes. Therefore, it is important that the emission wavelength can be tuned and enhanced by various approaches.In this dissertation, the spectral modulation of upconversion emissions has been achieved by both changing the dopant concentration and coupling the upconversion nanocrystals with noble metal nanostructures (i.e. surface plasmonic resonance). The relative spectral intensity can be tuned from 0.5 to 3 and the single wavelength emission can be enhanced by over 12 fold.These findings open a new pathway to rationally modulate the upconversion emission, and can broadly impact in areas including biomedical imaging, sensing and therapeutics, as well as enable new opportunities for energy harvesting and conversion