Ping Xiao,Song Ye,Huazhen Liao,Yanling Shi,Deping Wang
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.
To further enhance the photocatalytic performance of BiOCl, a facile hydrothermal reduction reaction was used to synthesize the reduced graphene oxide- (rGO-) modified ternary compound photocatalyst β-NaYF 4 :Yb 3+ , Er 3+ @BiOCl-rGO (NYF–Bi-rGO). rGO prepared using a hydrothermal method showed good conductivity . Furthermore, the specific surface area of NYF-Bi-rGO was 20-fold larger than that of NYF, which is a quality that could prove highly advantageous for use in pollutant adsorption. In addition, the ternary photocatalytic system produced by rGO increased the absorption intensity of NYF-Bi in the visible light region, and caused a red-shift of the entire absorption cross-section. In particular, analysis of carrier migration showed the introduction of rGO promoted the separation of the photoelectron-hole pairs of BiOCl, inhibited its recombination and improved the photocatalytic efficiency of the ternary photocatalyst NYF-Bi-rGO.
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