Temperature and rhodamine B sensing based on fluorescence intensity ratio of Er3+ upconversion emissions

In this paper, we report the temperature and rhodamine B (RhB)-concentration sensing behavior of Ag/ZnO/Er3+:YbMoO4 composite films based on the fluorescence intensity ratio (FIR) of two green upconversion (UC) emissions which are ascribed to the 2H11/2/4S3/2 → 4I15/2 transitions of Er3+. Through the strong and non-overlapping green UC emissions, the FIR of the two green emissions is closely related to temperature in the range of 300–650 K, which shows a high sensing accuracy and the maximum sensitivity of 0.01574 K−1. Due to the wavelength-dependent absorption of dye molecules, the FIR of the two green UC emissions exhibits an excellent exponential relationship with the RhB concentration in the range of 0–1000 ppm, which is ascribed to the radiative energy transfer (RET) from the composite film to RhB molecules. It is anticipated that the FIR technique based on the UC luminescence of rare-earth ions is a potential method for multifunctional application both in thermometers and biosensors.