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We investigate the upconversion emission of CaWO4:Tm 3+ /Yb 3+ polycrystals prepared by the high-temperature solid-state method. The crystal structure of the polycrystals is characterized by means of x-ray diffraction. Under the excitation of a 980 nm continuous wave diode laser, the samples show intense blue upconversion emissions centered at 473 nm, corresponding to the 1 𝐺4→ 3 𝐻6 transition of Tm 3+ . The dependence of the upconversion emission intensity on the pump power of a laser diode is measured, and the results indicate that the two-photon and three-photon processes contribute simultaneously to the blue upconversion emissions. The possible multiphoton upconversion process and upconversion mechanisms are discussed.

The porthole die extrusion process of profiled cross-section hollow aluminum alloy is influenced by numerous factors, which brings inconvenience to the process design. In this paper, 7075 aluminum alloy is taken as an example, the fitting model of the ultimate load is analyzed by variance and regression analysis using response surface method (RSM). The influences of extrusion speed, friction factor and initial temperature on the change of extruded ultimate load are investigated systematically, and the important influence factors (initial temperature [Formula: see text] friction factor [Formula: see text] extrusion speed) to the load are determined eventually. By comparison, the error between the ultimate load model obtained after fitting and the calculated value is only 2.4%, further verifying the reliability of this model. The optimal objective is to minimize the ultimate load, then the optimum technological parameters are obtained by optimizing the process, where the initial temperature, the extrusion speed and the friction factor are 430[Formula: see text]C, 2.28[Formula: see text]mm/s and 0.31, respectively. The results provide a theoretical basis for the scientific design of the porthole die extrusion process of profiled cross-section hollow aluminum alloy.