1. Guangdong Provincial Institute of Metrology, Guangzhou 510405, China
2. College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
Abstract：A contactless self-calibration temperature sensor based on the rare-earth fluorescence was developed. The new temperature sensing film Yb@PSMM was prepared by dispersed K[Yb(Az)4] in poly (styrene-block-methyl methacrylate) and then attached to a clean quartz plate, and the optical properties of Yb3+ in this system under different temperature were investigated. The shape of the fluorescence emission spectrum of Yb3+ changed regularly with temperature, and the distribution of extra-nuclear electrons in the Stark cleavage sublevels of Yb3+ at different temperatures still obeyed Boltzmann distribution law. The natural logarithm (ln) of the ratio of the two characteristic emission peak areas at 900~990 and 990~1 150 nm in the fluorescence spectrum linearly varied with the reciprocal of temperature (1/T) from -195 to 105 ℃. Upon using this linear relation as the standard curve, this temperature sensing method exhibited a temperature resolution of 0.1 ℃ around 0 ℃. Compared with the reported luminescence temperature sensors, the new temperature sensor proposed in this paper had advantages as follows. Firstly, the Stokes shift of the selected luminescent material was larger than 500 nm, which effectively avoided the interference of environmental backgrounds. Secondly, due to the use of fluorescence integrated peak areas instead of fluorescence intensities, the influence of random errors introduced by the instrument or measurement was greatly reduced. Thirdly, by taking advantage of the radiometric relationship between the intensities of different fluorescence peaks in one compound, a reliable self-calibration was introduced in this system equality, which effectively reduced the influence of external factors such as the variation of fluorescent material concentration, geometric configuration, or light source intensity. Fourthly, as a rare-earth luminescence material, the sensing method could utilize the characteristics of long fluorescence lifetime, good fluorescence monochromaticity, and high fluorescence intensities. Fifthly, the temperature sensing film was almost insoluble and indiffusible in water, which was convenient for direct measurement of the in-situ temperature changes. Lastly, Yb3+emission was from 900 to 1 150 nm, due to the deep penetration of near infrared light, this temperature sensor would have a wide potential use in temperature-sensing and imaging of complex system. Further ensuring method for the measurement results of the temperature sensor was adopted in our measurement device: the irradiated spot size on the sample could be adjusted to be about 1 mm2, and the angle between the placement direction of Yb@PSMM film and the excitation light was set to be 225°. Thus, the influence of the reflected light was circumvented, but the fluorescent emission light was hardly affected.
Key words：Fluorescence; Temperature sensing; Lanthanide complex; Near infrared; Self-calibration
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