Time-resolved spectroscopic studies of lanthanides doped inorganic, hybrid and organic systems

Abstract

In this thesis, three main chapters are discussed, including an Er3+-doped Y2O3 system, a Yb3+-doped NaYF4 nanoparticle system and a Yb(F-TPIP)3 co-evaporated with a Zn(F-BTZ)2 organic system. The main discussion is about the underlying physics of lanthanides, sensitisation of lanthanide ions by using the time resolved spectroscopy method. The up- and down-conversion processes between Er3+ ion pairs in the Y2O3 system was systematically investigated using the time resolved spectroscopy method regarding different Er3+ doping concentrations. The measured lifetime gives direct evidence for differentiating the excited state absorption (ESA) and energy transfer (ET) mechanisms during up-conversion processes. Also, the looping mechanism is found by measuring the NIR luminescence lifetime. Most importantly, the red to green emission ratio change during up-conversion processes with doping concentration is explained by a combination of up-conversion route change and concentration quenching effect. A novel sensitisation of Yb3+-doped NaYF4 nanoparticles is demonstrated by capping a 1,2,3,4,5,6,7-heptafluoro-8-hydroxyanthracene-9,10-dione (HL) ligand to the nanoparticle surface. The HL ligand acts as an antenna which can absorb visible light (400 nm to 600 nm) and then transfers the excited energy to Yb3+ ions encapsulated in the NaYF4 host. Interestingly, the energy transfers from the HL ligand to Yb3+ ions near the surface and then migrates to the Yb3+ ions inside the core of nanoparticles and is proved by a systematic time resolved spectroscopy study. The integrated organic chromophore based-excitation is almost 300 times higher compared with the Yb3+ intrinsic absorption band based-excitation. The last main discussion is given to the sensitisation of Yb3+ ions in a co-evaporated organic system as the co-evaporated organic system is more optically desirable than either the Y2O3 or the nanoparticle system. Compared with the intrinsic sensitisation, two orders of magnitude times sensitisation of Yb3+ ions is demonstrated by co-evaporating Yb(F-TPIP)3 and the Zn(F-BTZ)2 chromophore, making it a suitable material for a waveguide amplifier. In summary, an Er3+-doped Y2O3 system is investigated as the fundamental study to understand the underlying physics, and then HL ligand and Zn(F-BTZ)2 chromophore are investigated as potential sensitisers for Yb3+-doped nanoparticles and organic systems separately. The study in this thesis should be useful not only for fundamental physics but also as a reference for the applications of lanthanides