The Effect Of Structure On Photoluminescence Properties Of Rare Earth Ions Doped Al₂O₃

Among the rare earth ions doped planar waveguides, the rare earth ions doped Al₂O₃ waveguides have attracted much attention in recent years. However, the luminescence mechanism of the rare earth ions doped Al₂O₃ is not fully clear. In the dissertation, the Er³⁺-doped Al₂O₃ and Er³⁺-Yb³⁺ co-doped Al₂O₃ have been prepared by the two processes, the sol-gel method using erbium nitrate [Er(NO₃)₃ 5H₂O] and ytterbium nitrate [Yb(NO₃)₃ 5H₂O] as dopants and the technique in situ by sintering the Er ion implanted γ-A100H xerogel films, respectively. The effect of Er³⁺, Yb³⁺ doping concentration and sintering temperature on the structure and photoluminescence (PL) properties has been systematically studied, in order to explore the luminescence mechanism of Er³⁺ and sensitzation of the luminescence of Er³⁺ by Yb³⁺ in Al₂O₃ matrix materials.The Er³⁺-doped Al₂O₃ powders have been prepared by the sol-gel method, using the aluminium isopropoxide [Al(OC₃H₇)₃]-derived γ-A100H sols, with the addtion of the Er(NO₃)₃· 5H₂O. The phase contents diagram for the Er-doped Al-O system with the doping concentration up to 20 mol% is presented at the sintering temperature from 550 to 1400 ℃. The different crystalline types of (Al,Er)₂O₃ phases, γ, θ, α, and two Er-Al-O phases, ErA1O₃ and AlioEr6024, are detected. The Er³⁺ doping in the Al₂O₃ phases has a significant effect on phase transformations for the γ→θ and θ→α, indicating the enhancement for stability of the γ and θ phases. The Er³⁺ doping promotes the non-crystallization of the y and 0 phases. The 0-1.5 mol% Er³⁺-doped Al₂O₃ films on the thermally oxidized SiO₂Si(100) substrates are obtained in the dip-coating process by the sol-gel method. The continuous Er³⁺-doped Al₂O₃ films with the thickness of about 1.2 μm are observed for 9 dip-coatings at the sintering temperature of 900 ℃. The aggregate size for the Er³⁺-doped Al₂O₃ films increases from 30-50 nm to 100-300 nm with increasing the Er³⁺ doping concentration from 0 mol% to 1.5 mol%. The γ-Al₂O₃ phase with a (110) preferred orientation is produced for the Al₂O₃ film.The phase structure has an evident influence on the PL properties for the Er³⁺-doped Al₂O₃ materials. At the 1 mol% Er³⁺ doping concentration, the PL intensity of the Er³⁺-doped Al₂O₃ powders increases with the phase structure changed from γ→θ→α. For the γ and θ phases, the PL spectra of the full widths at half maximum (FWHM) of about 55 nm are observed with a main peak at 1.533 μm and a side peak at 1.550 μm. The PL spectrum is observed with the main sharp peak at 1.533 μm and many sharp side peaks at the different wavelengths for the a phase. With the same phase mixture of y and 0 in minor amounts with the different Er³⁺ doping concentration, the stronger PL intensity is detected with the 0.5 mol% and 1 mol% Er³⁺ doping concentration, and decreases with further increasing the Er ³⁺ doping concentration. The y and 0 phases obtained in the Er³⁺ doping concentration range of 0.1-2 mol% at the sintering temperature range of 800-1000 ℃, are fit for the waveguides due to the stronger PL intensity and broader FWHM. The PL spectra for y, 0, and a phases are analyzed using the symmetry group theory. The Er³⁺ doping in the y and 0 phases has multiplicity of sites and environments due to the disordered nature of these two phases. The inhomogeneous...