Temperature And Light Irradiation On The Rare Earth Doped Luminescent Properties Of Oxide Nano-crystal And Glass

In this thesis, there are two sections. One is about of temperature-dependence of luminescence of Eu3+and Tb3+doped in oxide glass and nanocrystalline Y2O3; the other is about of light-induced luminescent and structural change in nanocrystalline Y2O3: Tb. The creative works are as follows:(1) Euand Tb doped nanocrystalline Y2O3 with different sizes were prepared by combustion synthesis. Dependences of particle size, crystallinity and fluorescence characteristic on ratio of Gly/Y(NO3)3 and annealing temperature were studied. It can be concluded that charge transfer band in nanocrystalline Y2O3: Eu3+ has no direct connection with size, but depends on crystallinity.(2) The radiative transition rate of 5D1-7F1 and the nonradiative transition rate of 5D1- 5D0 in cubic nanocrystalline Y2O3: Eu3+ were obtained by measuring thetemperature-dependence of the fluorescence intensity and lifetime. The results indicate that the radiative and nonradiative rates both increase with decreasing particle size. The increase of radiative transition rate with decreasing particle size was attributed to the lower symmetry surrounding the Eu3+ ions, while the increase of nonradiative transition rate to the extra nonradiative transition channels caused by surface defects.(3) Under excitation of 488 nm, temperature-dependence of emission intensity of the 5D4-7FJ transition in nanocrystalline Y2O3 :Tb was studied. In nanocrystalline, there appeared two maximal intensities. They are at 280 K and 590 K respectively; In the bulk powder, only one maximal intensity at 280 K appeared.(4) Light-induced spectral change and its restore processes in the dark in nanocrystalline Y2O3: Tb were studied. It was observed that the intensity in 4f5d bandincreased by ultraviolet and visible irradiation. The smaller the particle size and the shorter the wavelength is, the larger the light-induced luminescent enhancement is. Two restore components were observed, corresponding to two defects, the internal and the surface. The studies on electron spin resonance (EPR) spectra indicate that optical irradiation eliminated the dangling Y-O bonds in the surface.(5) Under 488 nm excitation, temperature-dependence of emission intensity of Eu3+ in silicate glasses was investigated from 77 K to 670 K. It was observed that the total emission intensity of the Eu3+-ion in glasses had a maximum at a certain temperature. A unified theoretical model was given considering thermal activation, phonon-assisted absorption and nonradiative energy transfer processes.(6) The relationship between the fluorescence and the composition in niobate-silicate and niobate-phosphate glasses was studied. The results indicate that in niobate glasses, as the concentration of Nb2O5 increases, the covalence becomes strong, the symmetry becomes low and the electron-phonon coupling becomes strong, thus the lifetimes become short, the nonradiative transition processes and the temperature-quenching become strong and the value of crystal field parameter B20 becomes small.