Extended color tunability and efficient white-light generation through the construction of β-NaYF4: Yb3+/Tm3+/Ho3+ @NaYF4 core-shell structured nanocrystals

The ability to increase the emission intensity and turn the emission color of upconversion nanocrystals (NCs) will greatly enhance their application scopes. In this research, the sub-10 nm pure β-NaYF 4 : Yb 3+ /Tm 3+ /Ho 3+ core NCs were prepared by using sodium oleate (NaOA) as sodium source instead of the traditional NaOH, based on which the β-NaYF 4 :Yb 3+ /Er 3+ @NaYF 4 core-shell NCs were successfully obtained with seed-mediated growth method. The spectral measurement and the calculated CIE color coordinates revealed that the growing of inert NaYF 4 shell on the active NaYF 4 : Yb 3+ /Tm 3+ /Ho 3+ core NCs can not only effectively increase the upconversion emission intensity, but also realize extended tunable emission from blue to orange by turning Ho 3+ concentration, and a strong white light emission with chromaticity coordinates of (0.32, 0.33) can be obtained in the NaY 0.77 F 4 :0.2Yb 3+ /0.01Tm 3+ /0.02Ho 3+ @NaYF 4 core-shell NCs. Furthermore, the extended color tunability and efficient white white-light generation in the core-shell NCs were demonstrated by NCs-PMMA nanocomposites under 980 nm excitation. The results suggested that the β-NaYF 4 :Yb 3+ /Er 3+ @NaYF 4 core-shell NCs have promising applications in optoelectronic devices such as light emitting diode and three-dimensional display.