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Lanthanides in Luminescent Thermometry Chapter 281 405 l Dual-center thermometers are more effective in the cryogenic range, reaching Sm 1⁄43%K1 and dT1⁄40.2 K, for DE1⁄4600 cm1 and dD/D1⁄40.5% (portable spectrometers). l Although for T<70 K, Sm <0.1%K1, and dT>1 K, these values can be improved by one order of magnitude if PMT detectors are employed. l To shift the operating range to temperatures around room temperature, the energy gap between the two thermally coupled levels must be larger than 1000 cm1, which is much easier to accomplish if the Ln3+ ions are encapsulated into a polymer or an organic–inorganic hybrid host. l Single-center thermometers are not effective in the cryogenic range, being more appropriate for high temperatures (T>200K), with thermometric parameters analogous to those obtained for dual-center examples (for sim- ilar DE values). l The operating range can be shifted to higher temperatures increasing DE; however, as it is achieved at the cost of lowering the thermal coupling between the emitting states, caution must be taken to ensure that the two levels still remain thermalized in a thermodynamically quasi- equilibrium state. The illustrative Sm values plotted in Fig. 28 are entirely in accord with these conclusions validating the general principles of the single- and dual-center models described in this review, and anticipating the possibility of employing these models to design new thermometers with optimized and predicted performance. The main challenges that are currently facing scientists in the field are: l To design nanothermometers for bioapplications and nanomedicine. New nanostructures whose emission and absorption bands lie within the so-called biological windows (650–950 and 1000–1350 nm), where tissue scattering and absorption are minimized (Cero ́n et al., 2015; Smith et al., 2009; Weissleder, 2001), optically active in biological medium, biocom- patible, and easily uptaken by cells are mandatory to develop thermometry in nanomedicine. l To record time-resolved intracellular temperature maps with spatial and temporal resolutions better than 1 mm and 1 s, respectively. Despite the considerable amount of research on intracellular thermometry carried out over the past 3–4 years, accurate and high-resolution temperature distribu- tions within living cells have not yet been satisfactorily addressed. l To improve the thermometers’ spatiotemporal resolution below 1 mm–1 ms values. The temperature mapping in optoelectronic circuits is demanding for techniques combining high spatial and high temporal resolutions, compati- ble with the continuous high-rate data processing and miniaturization of the modern semiconductor devices. Luminescence will certainly play an important role in this process.PDF Image | HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS
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