Synthesis And Upconversion Luminescence Of Surface Coating Of Tm³⁺-Yb³⁺ Ions Dpoed Gd₂O₃ Nanoparticles

Rare-earth ions are suitable to be upconversion luminescent materials,for that they have stable physcial and chemical property,rich energy levels in the ultraviolet-visible-near infrared spectral region,and lony lifetime of excited state.Upconversion luminescence materials have been extensively applied in several areas such as detection of infrared radiation,color displays,anticounterfeit,upconversion laser and biological fluorescence labeling etc.However,due to the larger specific surface area of upconversion nanomaterials,numerous surface effects,such as lattice distortion,broken bond,surface adsorbate and other surface defect inevitably weaken the luminous intensityand and enhanced the nonradiative process.These have constrained the development of upconversion luminescence materials.How improve luminescent efficiency of upconversion luminescence materials has become a problem.In this thesis, as substrate Gd2O3 which possess excellent optical and physicochemical properties,doped Tm3+ and Yb3+ ion.The approaches of enhancing the emission efficiency of rare-earth materials were studied based on the luminescence mechanism.The main contents and the results are obtained as follows1. The nanocrystals Gd2O3:Tm3+ -Yb3+ were synthesized by the coprecipitation method. At 976nm excitation, Tm3+ ion energy and 976nm the energy no match, Gd2O3: Tm3+ is almost no the upconversion luminescence.After Gd2O3 added Tm3+ and Yb3+ ions, the bright blue (485nm) and strong near infrared (NIR) (808nm) upconversion luminescence were observed at room temperature under 976 nm LD laser.Beacause Yb3 + ions have absorption section near the 976nm, Yb+ ions can transfer energy to Tm3+ ions through non-resonant form.When Tm3+ ions absorbed non-resonance energy,Tm3+ generated energy level transition, resulting in blue light and near infrared light. In the process Yb3+ ions were as sensitization.The efficiency of upconversion luminescence of Gd2O3:Tm3+ -Yb3+ nanoparticles have greatly improved.Energy level diagram of Tm3+ -Yb3+ ions with Srark splitting explain energy transfer process between Tm3+ and Yb3+ ion.2. The upconversion Gd2O3:Tm3+ -Yb3+ nanoparticles coated with silica were synthesized by the microemulsion method. The TEM and SEM images demonstrated that the as-prepared samples were the core-shell structure nanoparticles. The NIR emission intensity of Gd2O3:Tm3+ -Yb3+ nanoparticles was increased by 8 times due to the SiO2 coating under 976 nm LD laser. The improved mechanism in upconversion luminescence intensities,when Gd2O3:Tm3+ -Yb3+ nanoparticles coated SiO2 shell,the "sleep " ions of the surface of nanoparticles i are "activated", new isolated luminescence centers of rare earth ions on the surfaces of nanoparticles will be formed and weakened effect on the surface effect.Upconversion luminescence intensity increased.3. We compared the microemulsion methodand with the second coated method of SiO2 coat Gd2O3:Tm3+ -Yb3+ nanoparticles.The results show that dispersion and luminescence intensity of nanoparticles were synthesized by the microemulsion better than traditional secondary coated method.In summary, we successfully enhanced the emission efficiency of Tm3+ ions by sensitization method and surface coat method, based on the mechanism influencing the luminescence efficiency.