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All of the samples were synthesized by sol-gel methods.Two approaches to charge compensation,(i) 2Ca2+→Yb3++M+,where M+ is an alkali ion like Li+,Na+ and K+,and(ii) indirect charge compensation:3Ca2+→2Yb3++vacancy,were studied in detail.It was found that charge compensation would be very beneficial for the growth of the grains,especially in Li+ ions added samples.All the grains were homogeneously spherical with less boundaries;in addition,a great variety of the absorption ability in different charge compensation samples were observed:in comparison with the phosphors without charge compensation,indirectly charge compensated and Li+ ions added phosphors showed much stronger absorption strength in the ultraviolet(UV) region whereas that of Na+ and K+ ions added samples was much weaker;moreover,measurements of the emission intensities showed that:in comparison with the phosphors without charge compensation,the visible emission intensity from MoO42-decreased a lot in indirectly charge compensated and Li+ ions added phosphors,whereas there was a remarkable increase of the near infrared(NIR) emission intensity from Yb3+ ions in the two types of samples under 266 nm excitation,implying more efficient energy transfer(ET) from MoO42-to Yb3+ ions;at last,measurements and analysis of the decay curves of the visible 495 nm emission were carried out,and it was found that the energy transfer from MoO42-to Yb3+ ions were more efficient in the two above types of phosphors.The theoretical quantum cutting(QC) efficiency was also improved greatly.Overall,the addition of Li+ ions would be very beneficial for the morphology of the powders in addition to the growth of the grains.It was advantageous to increase the downconversion(DC) quantum efficiency;however,indirect charge compensation would enhance the NIR emission intensity to the most for its strongest absorption ability in the UV region.
All of the samples were synthesized by sol-gel methods. Two approaches to charge compensation, (i) 2Ca2 + → Yb3 ++ M + where M + is an alkali ion like Li +, Na + and K +, and (ii) indirect charge compensation: 3Ca2 + → 2Yb3 ++ vacancy, were studied in detail. It was found that charge compensation would not be very beneficial for the growth of the grains, especially in Li + ions added samples. All the grains were homogeneously spherical with less boundaries; in addition, a great variety of the absorption ability in different charge compensation samples samples were observed: in comparison with the phosphors without charge compensation, indirect charge compensated and Li + ions added phosphors showed much stronger absorption strength in the ultraviolet (UV) region where that Na + and K + ions added samples was much weaker; moreover, measurements of the emission intensities showed that: in comparison with the phosphors without charge compensation, the visible emission intensity from MoO42-decreased a lot in indirectly charge c ompensated and Li + ions added phosphors, there was a remarkable increase of the near infrared (NIR) emission intensity from Yb3 + ions in the two types of samples under 266 nm excitation, implying more efficient energy transfer (ET) from MoO42-to Yb3 ions ; at last, measurements and analysis of the decay curves of the visible 495 nm emission were carried out, and it was found that the energy transfer from MoO42-to Yb3 + ions were more efficient in the two above types of phosphors. (QC) efficiency was also improved greatly. Overall, the addition of Li + ions would be very beneficial for the morphology of the powders in addition to the growth of the grains. It was advantageous to increase the downconversion (DC) quantum efficiency; however, indirect charge compensation would enhance the NIR emission intensity to the most for its strongest absorption ability in the UV region.