Effect of silica surface coating on the luminescence lifetime and upconversion temperature sensing properties of semiconductor zinc oxide doped with gallium(III) and sensitized with rare earth ions Yb(III) and Tm(III)
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Optical sensing of temperature by measurement of the ratio of the intensities of the 700 nm emission and the 800 nm emission of Ga(III)-doped ZnO (GZO) nanoparticles (NPs) and of GZO NPs coated with a silica shell are demonstrated at 980 nm excitation. It is found that the relative sensitivity of SiO2@Yb/Tm/GZO is 6.2% K−1 at a temperature of 693 K. This is ~3.4 times higher than that of Yb/Tm/GZO NPs. Obviously, the SiO2 shell structure decreases the rate of the nonradiative decay. The decay time of the 800 nm emission of the Yb/Tm/GZO NPs (15 mol% Ga; 7 mol% Yb; 0.5 mol% Tm) displays a biexponential decay with a dominant decay time of 148 μs and a second decay time of ~412 μs. The lifetime of the Yb/Tm/GZO NPs at 293 K, and of the SiO2@Yb/Tm/GZO NPs are ~412 μs. Both the Yb/Tm/GZO and SiO2@Yb/Tm/GZO can be used up to 693 K. These results indicate that the SiO2 shell on the Yb/Tm/GZO is beneficial in terms of sensitivity and resolution.
KeywordsCore@shell structure Upconversion luminescence Fluorescence lifetime Relative sensor sensitivity
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The authors declare that they have no competing interests.
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