Synthesis And Photophysical Properties Of Core-shell Nanohybrids Embedded With Rare Earth Complexes

The main contents in this thesis are as follows. 1. The core-shell silica hybrid spheres embedded with europium complex nanoclusters were fabricated by a modified St?ber method for the first time. The core-shell hybrid spheres possess smooth surfaces,uniform size and monodispersity. Under the excitation of ultraviolet light, the hybrid spheres exhibit the characteristic luminescence of the Eu³⁺ ions. 2. The hybrid spheres were studied on their luminescence properties by using laser spectroscopy methods. Two luminescence centers were identified in both of the pure complex and the hybrid spheres. Our experimental results show that, in the hybrid spheres, the silica shell has different influences on the two luminescence centers of Eu³⁺ ions. The center on the complex surface is greatly activated after incorporated into silica spheres. 3. Further experimental and theoretical analysis shows that the quantum yield of Eu³⁺ ions in the silica nanospheres is enhanced due to the decrease of nonradiative transition rate. Additionally, the hybrid spheres exhibit an improved thermal stability compared with the pure rare earth complex. 4. Dispersed in different dielectric polymers, the Eu³⁺ ions in the hybrid spheres showed different spontaneous emission rates due to the modification of dielectric boundaries. The higher the refractive index of surrounding medium, the higher the local optical density of states in the hybrid spheres. This results in higher spontaneous emission rates as well as shorter lifetimes of excited states in the hybrid spheres. 5. The core-shell titanium dioxide hybrid spheres embedded with europium complex nanoclusters were fabricated and their optical properties were investigated. It was confirmed by laser spectroscopy that there are two luminescence centers in the hybrid spheres, just like in Eu(DBM)3phen/SiO2 hybrid spheres. The fluorescent lifetime of Eu³⁺ ions in the TiO₂ spheres is shorter than that in the SiO2 spheres, which offered experimental evidence to the theory on local optical density of states and peripheral refractive index in a nanosphere. 6. Tb(AcAc)3phen/SiO2 hybrid spheres were synthesized by using the modified St?ber method and their luminescent properties were also investigated. Under the excitation of 330 nm, the Tb(AcAc)3phen/SiO2 hybrid spheres display the characteristic luminescence of the Tb3+ ions, which means that terbium complex has been introduced into the silica spheres. The modified St?ber method is an efficient way in incorporating various rare earth complexes into silica (or titanic oxide) spheres, and various kinds of hybrid spheres with different fluorescence can be synthesized by using it. The rare earth ions located in coordination ligands are effectively isolated from the host and have higher radiative rates due to the deduced quenching effect from the host. Therefore, without any annealing, the hybrid spheres can emit strong characteristic fluorescence of rare earth ions. 7. Yb3+ and Tm3+ co-doped yttrium fluoride nanocrystals were synthesized by a hydrothermal method, and then the nanocrystals were incorporated into silica shells with various thickness to form YF3:Yb,Tm/SiO2 nanohybrids. Under 978-nm excitation from an IR diode laser, the nanohybrids exhibit strong ultraviolet and violet upconversion luminescence. By controlling the thickness of silica shells, greatly enhanced upconversion luminescence were observed at short wavelengths in the nanohybrids for the first time. The upconversion luminescence properties of the nanohybrids and the influences of the silica shells as well as their thickness on them were studied. The core-shell nanohybrids we investigated here have significant potential applications in biological image marks, active photonic band gap materials, luminescence and display devices, microlasers, data storages, nanosensors, etc.