In this work, a solvothermal process was used to synthesize the β-NaYF,4,:20%Yb,3+,/2%Er,3+, core nanoparticles(NPs) and β-NaYF,4,:20%Yb,3+,/2%Er,3+,@β-NaYF,4,:,x,%Yb,3+,(,x,=0, 20, 50, 70, 100) core-shell NPs. The size of the core NPs and core-shell NPs is about 30 nm and 40 nm respectively, implying that the thickness of the layer is 5 nm. After coating a β-NaYF,4, shell without Yb,3+, doping, the upconversion(UC) intensity is increased with a factor of 14 and 25 for green emission and red emission respectively, resulting from the suppression of deexcitation of Yb,3+, ions by the core-shell structure. However, the UC intensity is decreased dramatically with the increasing Yb,3+, ions concentration in the shell, due to the inefficient energy transfer process between the Yb,3+, ions in the shell and the Er,3+, ions in the core caused by the large distance between them. As the β-NaYF,4, shell completely converts to β-NaYbF,4, the UC intensity decreased 98.8% and 99.4% for green and red emission, respectively.
rare earthupconversionenergy transferβ-NaYF4
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