| Energy saving and environmental protection are the most urgent problem in 21st century. On one hand, clean energy such as solar energy should be more and more utilized. On the other hand, how to reduce energy consumption thus realizing a green economic development based on energy saving and environmental protection is important.Solar cell can efficiently transfer sunlight to electric energy but the space for raising photoelectric conversion efficiency is limited by increasing the purity of crystal silicon. To catch more sunlight energy is a new approach to promote the solar cell efficiency. The band width of crystalline silicon is 1.1ev, theoretically, short wave sunlight (<1127nm) could generate photoelectric effect in crystalline silicon. However, the sunlight energy that can be used efficiently is basically focused in 400nm-700nm high energy wave band, less than 40% of the whole sunlight energy. So, it is a valuable work to learn how to transfer the sunlight wave in 700nm-1127nm band and infrared region (>1127nm) into high energy wave band which can efficiently generate photovoltaic effect in crystalline silicon. Besides, LED, especially white light LED is a kind of green lighting thanks to its advantages such as outstanding energy conservation, high brightness, long lifetime, small volume (compared to conventional light). The key to the two devices mentioned above is to explore excellent upconversion and downconversion luminescence materials. Double or triple metal oxide hybrids with different rare earth dopants have been studied, listed as follows:(1) Upconversion properties of titania-zirconia nano composite with double rare earth dopants:Titania-zirconia complex material is synthesized for matrix.Two rare earth dopant systems, Tm3+-Yb3+ and Er3+-Yb3+ are co-doped in the complex material. The luminescence property demonstrate that under 980nm excitation, Tm3+-Yb3+ co-doped titania-zirconia nano composite have two upconversion bands in blue and red wave region. ZT0.4 (40% ZrO2-60% TiO2-1% Tm3+-4% Yb3+) composite have the best upconversion effect. Er3+-Yb3+ co-doped titania-zirconia composite have two upconversion bands in green and red wave region. Upconversion emission intensity in green and red band can be changed by adjusting the dopant concentration.(2) Preparation and luminescence properties of Ce:YAG aluminium garnet phosphor:single crystal Ce:YAG phosphor was synthesized by co-precipitation method, followed with a thermal process (1300℃,2h). Particle size of the phosphor is about 500nm, and agglomerated particle is about 15-20μm. Ce:YAG phosphor by co-precipitation method can be excited by 465nm blue light excitation and exert a wide emission band between 500-600nm(yellow-green light,5d-4f characteristic transition, Ce3+), the emission can be mixed with its 465nm blue exciting light and turn into white light of high brightness. Systematic research on dopants and thermal process condition indicate that anion (especially anion group), thermal process temperature and atmosphere are key factors to luminescence property.(3) Preparation and luminescence properties of Eu2+ doped or Eu2+-M (M=Ce3+, Gd3+) co-doped Sr3SiO5 warm white phosphor:Eu2+:Sr3Si05 phosphor was synthesized by sub-precipitation method, particle size is about 30μm. The concentration of Eu2+ dopant will greatly influenced the luminescence intensity at 443nm and 592nm emission. With the rising concentration of Eu2+ dopant (0.5%-12%), the luminescence intensity at 443nm rise initially and then drop after the peak point (Eu2+:1%); a same variation trend can also be observed at 592nm while its peak point is at 3%Eu2+ concentration. Study on co-doped samples demonstrate that:Gd3+ dopant have a red-shift effect on 443nm emission of Eu2+:Sr3Si05 while existing a slight decrease on its intensity, and 592nm emission disappear; Ce3+ will intensify both of the two band emissions of Eu:... |
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