Shiping Wu

EFFECT OF HfO2-CODOPING CONCENTRATION ON THE OPTICAL PROPERTIES OF Er3+-DOPED LiNbO3

A series of Hf, Er co-doped LiNbO3 crystals were grown by Czochralski technique with 1 mol% of Er2O3 and with 2, 4, 6 and 8 mol% of HfO2, respectively. The optical damage resistance of Hf:Er:LiNbO3 crystals was studied by the transmitted beam pattern distortion method. The optical damage resistance of Hf (6 mol%): Er:LiNbO3 crystals is about two orders of magnitude higher than that in Hf:Er:LiNbO3. The X-ray power diffraction, the ultraviolet-visible absorption spectra and the infrared absorption spectrum were measured and discussed in terms of the spectrometric characterization and the defect structure of crystals. The results showed that with mild co-doping with HfO2, Er3+ substitutes Nb5+, whereas with heavy co-doping, a part of Er3+ substitutes Li+. The structure defects were discussed in this paper to explain the improvement of the optical damage resistance in the Hf:Er:LiNbO3.

EFFECT OF Li/Nb RATIO ON GROWTH AND SPECTROMETRIC CHARACTERIZATION OF Hf:Fe:LiNbO3 CRYSTALS

Hf:Fe:LiNbO3 crystals were grown by the Czochralski technique with various ratios of Li/Nb = 0.946, 1.05, 1.20 and 1.38 in the melt. The crystal composition and defect structure were analyzed by XRD, UV-Vis and IR spectroscopy. The results show that the threshold concentration of Hf in LiNbO3 crystals decrease with the increasing of the Li/Nb ratio; when the Li/Nb ratio is 1.05, the threshold concentration of Hf is less than 2 mol%, largely under the threshold concentration of Hf ions in congruent Hf:Fe:LiNbO3 crystal (4 mol).1–3 With the increase of Li/Nb, Hf ions first replace the ; when the concentration of Hf ions is higher than the threshold value, Hf ions occurs on normal Nb and Li sites.

Experimental and numerical study on formation mechanism of linear macro-segregation in low-pressure die casting of Al-Cu-Mn-Ti Alloy

The formation mechanism of linear macro-segregation in Al–Cu–Mn–Ti alloy cylindrical shell casting was studied by characterizing samples by X-ray detection, microscopic examinations, composition analysis, and simulation of the heat transfer of Al–Cu–Mn–Ti alloy cylindrical shell casting in the solidification process. Numerical and experimental results indicated that linear macro-segregation always occurred in the portion of casting connected with the slit gating system, because of the great hot tearing tendency, the hot cracks formed could be fed by the melt through the slit gating system with an excellent temperature gradient and feeding angle. According to significant effect of floatation of lower density α-Al grains, the solute gradient was formed along the vertical direction of the slit gating system. The hot cracks near the bottom of casting were fed by melt with high concentration of Cu and so, they were cicatrized by the eutectic structure/α-Al + Al2Cu at a temperature of 548℃.

JUDD–OFELT THEORY ANALYSIS AND SPECTROSCOPIC PROPERTIES OF Ho:LiNbO3

A series of Ho:LiNbO3 crystals with various concentration of Ho2O3 were grown by Czochralski technique. Transmittance spectrum, absorption spectrum and modified Judd–Ofelt approach have been used to investigate its spectroscopic properties. Ho concentrations in crystals were analyzed by an inductively-coupled plasma optical emission spectrometry (ICP-OE/MS). The results of the spectroscopic analysis of transition strengths for Ho ion in a series of Ho:LiNbO3 crystals with various Ho content are reported. It is concluded that all the Ωλ values of the Ho ion decrease with increasing Ho content. For Ho (4 mol%): LiNbO3, the obtained intensity parameters and radiative lifetime of the 5I5 level are: Ω2=5.75×10-20 cm2, Ω4=22.69×10-20 cm2, Ω6=14.10×10-20 cm2, and τ=4.08 ms respectively. The results showed that the Ho2O3-codoped LiNbO3 crystal increases the Ho ion radiative lifetimes, but has less influence on the fluorescence branching ratio.