Temperature and rhodamine B sensing based on fluorescence intensity ratio of Er3+ upconversion emissionsElectronic supplementary information (ESI) available. See DOI: 10.1039/c7ra09977k

In this paper, we report the temperature and rhodamine B (RhB)-concentration sensing behavior of Ag/ZnO/Er 3+ :YbMoO 4 composite films based on the fluorescence intensity ratio (FIR) of two green upconversion (UC) emissions which are ascribed to the 2 H 11/2 / 4 S 3/2 → 4 I 15/2 transitions of Er 3+ . 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. Fluorescence intensity ratio technique of upconversion emissions of Er 3+ can be used for both temperature and RhB concentration sensing.