Study On The Upconversion Luminescence Properties Of Er³⁺, Yb³⁺ Doped Rare-earth Titanate Compound Nanocrystals

Up-conversion luminescence materials mainly are attributed to inorganic material which is doped byrare-earth elements. These materials using the characteristics of metastable energy level of rare-earthelements, excitated with long wavelength light, it can absorb multiple low-energy long-wave radiation,through the photon added, and emitted the high-energy short-wave radiation, which make the infraredpeople can’t see into visible light. With the rapid development of nanotechnology， nano-scaledup-conversion materials have a variety of potential applications in many fields, such as color displays,photo-electronic, infrared detection and up-conversion lasers in recent years. These materials havegradually been considered to be the next generation novel luminescent materials due to these nanoscaledup-conversion materials have many miraculous properties compared with the bulk materials. Among thenanoscale materials, pyrochlore type complex oxides are thought to be the ideal luminescent materialsowing to their excellent chemical and thermal stability. Pyrochlore type complex oxides are used in theareas of information display, light engineering, optical communication. Rare-earth titanates are cubicpyrochlore-type oxides，which have promising applications in lithium ion batteries，catalysts，phosphors，ionic conductors，and resistance to radiation damage．In order to explore novel luminescence systems withhigh luminescent efficiency, in this thesis，we synthesized several titanate nanomaterials by sol-gelmethod and studied their up-conversion luminescence properties systemically. The main contents andimportant results are listed as follows：1. We successfully prepared nanocrystalline Er³⁺doped Gd₂Ti₂O₇phosphors by the sol-gel method.The results show that Gd₂Ti₂O₇:Er³⁺is cubical phase and sphere. We can observe that all these nanocrystalscan give the green emission and red emission, which are attributed to the intra-4f transition of⁴H_11/2,⁴S（3/2）â†'⁴I_15/2 and⁴F_9/2â†'⁴I_15/2 of Er³⁺ions, respectively. The optimal doping concentration of Er³⁺is found tobe4mol%.₂. We prepared nanocrystalline Y3₂Ti₂O₇:Er³⁺phosphors with various Er³⁺doping concentration anddifferent annealing temperatures by sol-gel method. The up-conversion emission spectrum of the samplewas measured under the excitation of a980nm continuous wave diode laser. The optimal doping content and annealing temperatures of Er³⁺are found to be5mol%and800oC.3. Nanocrystalline La₂Ti₂O₇:Er³⁺phosphors with different annealing temperatures and various Er³⁺doping concentration were prepared by sol-gel method. The particle morphology was approximately sheetand particle that form agglomerates of₂00-300nm in size. The Er³⁺doped La₂Ti₂O₇nanocrystalsabsorbing the980nm photons can produce the up conversion (5₂5,549, and660nm;²H_11/2â†'⁴I_15/2,⁴S_3/2â†'⁴_15/2 and⁴F_9/2â†'⁴I_15/2, respectively) photoluminescence. The green and red emissions originated from atwo-photon up conversion process. The optimal annealing temperature was1000oC and appropriate dopingconcentration is13mol%Er³⁺.4. Er³⁺doped A₂Ti₂O₇（A=La, Y, Gd），Er³⁺and Yb³⁺ions co-doped La₂Ti₂O₇nanocrystals weresynthesized by sol-gel method. The up-conversion luminescence intensity of Er³⁺ions is enhanced greatlyby addition of various contents of Yb³⁺ions, and the optimal doping concentration was3mol%of Yb³⁺ions.