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).

Abstract

Optical sensing of temperature by measurement of the ratio of the intensities of the 700nm emission and the 800nm emission of Ga(III)-doped ZnO (GZO) nanoparticles (NPs) and of GZO NPs coated with a silica shell are demonstrated at 980nm excitation. It is found that the relative sensitivity of SiO2@Yb/Tm/GZO is 6.2% K-1 at a temperature of 693K. 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 800nm 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 148μs and a second decay time of ~412μs. The lifetime of the Yb/Tm/GZO NPs at 293K, and of the SiO2@Yb/Tm/GZO NPs are~412μs. Boththe Yb/Tm/GZO and SiO2@Yb/Tm/GZOcan be used up to 693K. These results indicate that the SiO2 shell on the Yb/Tm/GZO is beneficial interms of sensitivity and resolution. Graphical abstract The enhancement the decay time and thermal sensitivity in the SiO2@Yb/Tm/GZO shell@core structure have been studied compared to the Ga(III)-doped Yb/Tm-doped ZnO (Yb/Tm/GZO). The SiO2@Yb/Tm/GZO have good thermal accuracy up to 693 °C.