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358 Handbook on the Physics and Chemistry of Rare Earths TABLE 2 State-of-the-Art Values for dD/D for Different Detectors Detector Minimum Type dD/D (%) Observations PDA 0.1 Low-cost detector incorporated in most portable spectrometers. Acquisition time on the millisecond range CCD 0.05 Detector for large-area mapping. Acquisition time on the millisecond range PMT 0.03 State-of-the-art radiation detector. Used in high-sensitive spectrometers. Acquisition time on the microsecond to the nanosecond range, per wavelength step 3.2.2 Experimental Determination of the Temperature Uncertainty The dT values are experimentally determined from the distribution of temper- ature readouts of a luminescence thermometer when it is at a certain reference temperature. The temperature that corresponds to each spectrum is obtained using a calibration curve and the standard deviation of the resulting tempera- ture histogram is the experimental dT of the luminescent thermometer. We illustrate this procedure for a chloroform suspension of NaYF4:Yb3+/Er3+ (18/2%) NPs at 3 g L1 (Fig. 4). The details on the temperature measurement using the Er3+ emission upon 980 nm IR excitation are given in Section 4.1.1. We first calibrated the luminescent thermometer using a standard K-type ther- mocouple probe immersed in the suspension container. Then, setting the tem- perature of the sample to 308 K, we measured the emission spectra with 250 ms integration time during 60 s (total of 240 measurements). We com- puted D according to Eq. (1), and the corresponding histogram presents a stan- dard deviation of 0.0078. Computing the temperature corresponding to each emission spectrum using the calibration curve, a new histogram of tempera- ture readouts is built (related with that based on D by the calibration curve). Notice that higher relative sensitivity values narrow the histogram of T in comparison with that of D (Fig. 4). This experimental procedure also allows estimating potential effects of the excitation light on the thermometer readout. For UV-excited Ln3+ complexes, for example, the absence of drifts on the temperature readout indicates the absence of measurable heating by the ligand-induced Stokes shift (Fig. 5A). In contrast, the local temperature of Nd3+- and Yb3+/Er3+-doped NPs notice- ably increases under NIR excitation (Fig. 5B), a reason why they are being used as a single heater–thermometer platform (Rocha et al., 2014a; Wawrzynczyk et al., 2012; Ximendes et al., 2016).PDF Image | HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS
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