Optical Properties In Rare Earth Doped Nanoparticle-Organic Molecule Hybrids

Optical energy transfer exists widely in luminescent materials.The energy transfer between quantum dots and organic molecules could lead to exchange of excitons,making it highly attractive for optoelectronic and photovoltaic applications.As excellent activator centers,rare earth(RE)ions possess rich 4f levels with energy covering visible and infrared spectral range.Therefore,energy transfer also takes place between RE ions and wxcitons inorganic molecules.The investigation of this thesis focuses on the energy transfer and optical properties hydird made up of RE-doped nanoparticles and organic molecules.Firstly,NaYF4:20%Yb3+/1%Er3+ nanoparticles were synthesized by coprecipitation method,which were then mixed with rubrene molecules to form a hybrid solution system.The energy transfer mechanism of the hybrid system and the effect of rubrene concentration on the energy transfer rate and spectra properties were investigated.Broadband upconversion emission covering infrared to visible spectral region is observed in a solution mixture of NaYF4:20%Yb3+/1%Er3+ nanoparticles and rubrene molecules.The energy transfer between NaYF4:20%Yb3+/1%Er3+nanoparticles and rubrene molecules involves two distinct mechanisms:rediative reabsorption and non-radiative resonance energy transfer.The results indicate that radiative energy transfer dominates in all the samples examined.The luminous efficiency increases with the concentration of rubrene,and concentration quenching that results in the decrease of efficiency is observe at high rubrene concentration due to strong self-absorption.Secondly,NaYF4:x%Nd3+(x = 0.5,1,2,5)nanoparticles were synthesized by coprecipitation method,and the surface adsorbed oleic acid(OA)was exchanged with OFBT molecules through a sonication-assisted process in liquid phase.The energy transfer mechanism in the NaYF4:x%Nd3+ coated with OFBT molecules and the effect of Nd3+ doping concentration on the luminescence properties of the materials were investigated.High-efficiency non-radiative resonance energy transfer is achieved in NaYF4:x%Nd3+ nanoparticles surface-modified OFBT molecules.The effect of Nd3+doping concentration on the luminous efficiency of the system is consistent with the self-concentration quenching of NaYF4:x%Nd3+.Moreover,the luminescence property of the system demonstrate obvious dependence on temperature and pH,thus enabling potential application for optical temperature sensing and pH nanoprobes.