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Lanthanides in Luminescent Thermometry Chapter 281 351 quantified accordingly to the relevant parameters: relative sensitivity, tempera- ture uncertainty, spatial and temporal resolution, repeatability (or test–retest reliability), and reproducibility. The emission mechanisms supporting single- and dual-center emissions are reviewed, together with the advantages and lim- itations of each approach quantified essentially by the relative sensitivity and the temperature uncertainty. Illustrative examples of the rich variety of systems designed and developed to sense temperature are provided and explored in Section 5. Finally, we would attempt to summarize the chapter and provide a brief prospective outlook in Section 6. 2 LUMINESCENT THERMOMETERS Historically, three main approaches to determine the temperature were fol- lowed in luminescent thermometry: (i) the spectral shift of a given transition, (ii) emission intensity measurements, using the integrated intensity of a single transition or of a pair of transitions, and (iii) lifetime measurements, using the decay profiles of emitting excited states (Fig. 1). The most obvious approach to infer the absolute temperature from lumi- nescence spectroscopy is to measure the intensities from two energy levels (or two Stark components of an excited state) in thermal equilibrium (see Section 4.1.1). The temperature scale is based exclusively upon the validity of the Boltzmann distribution and this nonempirical procedure was documen- ted initially for the 2H11/2 ! 4I15/2 and 4S3/2 ! 4I15/2 Er3+ transitions (Shinn et al., 1983; Weber, 1967) and for two Stark components of the 5D1,2 Eu3+ levels (Kusama et al., 1976). The noticeable feature of the 2H11/2/4S3/2 Er3+ pair of excited levels is that they are energetically close, the energy gap being $800 cm1 (Carnall et al., 1977), permitting the 2H11/2 level to be populated from 4S3/2 by thermal agitation (kBT $ 200 cm1 at room temperature) FIG. 1 Luminescent thermometers classification.PDF Image | HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS
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