Rare earth doped upconverting particles for different photonic applications*

Trivalent rare earth ions especially erbium (Er$^{3+})$ and ytterbium (Yb$^{3+})$ co-doped in various host nanoparticles are known for their extraordinary spectroscopic properties. A thorough optical characterization including the absolute upconversion quantum yield (QY) measurement is of critical importance in evaluating their potential for various photonic applications. In this paper, we will be presenting a measured absolute upconversion QYs for Yb$^{3+}$ and Er$^{3+}$ doped in La$_{2}$O$_{2}$S under 980 and 1550 nm excitation at various power densities. Comparison of absolute QYs for different concentrations of Yb$^{3+}$ and Er$^{3+}$ doped in La$_{2}$O$_{2}$S will be made for all the upconversion emissions with respect to reported most efficient upconverting phosphor NaYF$_{4}$ doped with 20{\%} Yb$^{3+}$ and 2{\%} Er$^{3+}$. Furthermore, applications of these phosphors in different areas such as bio-imaging, solar cell, security, etc. will be explored depending on the measured absolute upconversion quantum yields. In addition, preliminary results on in vitro imaging using upconverting nanoparticles as a contrast agent will be reported.