Synthesis And Luminescent Properties Of Low-dimensional Nanosized Ln₂O₃:RE (Ln=Y,Gd)

We prepared Y₂O₃:Ho/Yb nano-particles by a solution combustion procedure and Gd₂O₃:Er/Yb nanowires as well as nanoslices by a hydrothermal method. The thesis was carried out with the purpose of exploring the luminescent characterization of nano-materials codoped with rare earth ions and finding the physical nature. Luminescence properties, mechanism and dependence of luminescence intensity on pump power density were studied in the nano-materials. The main results and innovation are as follows: A. Y₂O₃:Ho/Yb system: 1. The total emission intensity was decreased and the intensity ratio of the red emissions of 5F5→5I8 to the green emissions of 5S2(5F4)→5I8 was increased with the decrease of particle size. The nonradiative relaxation rate was increased dramatically with the decrease of particle size due to a great number of surface defects. The increase of nonradiative relaxation led to the quenching of total emission intensity and the relative increase of the red emissions. 2. Under the excitation of 980nm diode laser, the up-conversion luminescence intensity was increased as the excitation power increased under lower excitation density, but was decreased in the case of higher excitation density. It was suggested that under intense laser irradiation some Ho³⁺ or Yb³⁺ were changed to other valence states through electronic tunneling processes. B. Gd₂O₃:Er/Yb system: 1. The Gd₂O₃: Er³⁺/Yb³⁺ nanocrystals were prepared by the hydrothermal method. The samples yielded nanoslices in the chemically neutral conditions and yielded nanowires in the alkalescent conditions. 2. The ratio of surface atoms to inner atoms in nanowires was decreased in comparison to that in nanoslices, and the nonradiative relaxation was decreased due to a great number of surface defects were involved. This led the intensity of upconversion luminescence to increase and the intensity of infrared emission to decrease relatively. 3. In Gd₂O₃:Er³⁺/Yb³⁺ nanowires, the intensity ratio of ²H_11/2-⁴I_15/2 to ⁴S_3/2-⁴I_15/2 increased dramatically with the increasing pump power, which was attributed to the increase of thermal populations in ²H_11/2 energy level caused by irradiation induced temperature increase.