PDF Publication Title:
Text from PDF Page: 416
Lanthanides in Luminescent Thermometry Chapter 281 381 a dual-center emission the problem is reduced to the single-center case. An illustrative example is the Y2O3:Yb3+/Ho3+/Tm3+ UCNPs (Pandey and Rai, 2013) in which the thermometric parameter involves the intensity ratio of 5F3 ! 5I8 (Ho3+, I1) and 1G4 ! 3H6 (Tm3+, I2) transitions (Fig. 14). Due to the close energetic position of the emitting levels, ($470 cm˗1) the authors observed an overlap between the Ho3+ and Tm3+ transitions, see the discus- sion in Section 4.1.2. The resulting energetic separation between the levels was found to be DE2DE11⁄4443.827.72cm1, in good agreement with the actual energy gap between the (Ho3+) and 1G4 (Tm3+) levels (473 cm1). This means that the difference between the activation energies for the two thermal quenching processes is mainly the energy gap between the two emitting levels, or, in other words, this suggests that both emitting levels are thermally depopulated through the same energy level. Another interesting example of a dual-center emission thermometer that fol- lows the same functional form of Boltzmann law (Eq. 25) is the Eu3+/Tb3+-doped APTES/TEOS organic–inorganic hybrid NPs (Brites et al., 2013b). The peculiar energetic position of the first excited triplet state of the acac ligand induces a con- tinuous decrease of the integrated intensities of the 5D4 ! 7F5 (I1) and 5D0 ! 7F2 (I2) transitions in the 10–330 K range (Fig. 17). Two different regimes are clearly discernible: for T < 175 K the I1 integrated area decreases stronger, when com- pared with that of I2, whereas for T > 200 K both I1 and I2 decay almost linearly. The switch between the two regimes occurs in the 175–200 K range. When we plot, in the second regime, the natural logarithm of D with respect to the inverse of the temperature, we find a linear relationship compatible with Eq. (39). In this case, the activation energies DE1 and DE2 involve the triplet host (or ligand) level FIG. 17 (A) Normalized integrated 5D4 ! 7F5 and 5D0 ! 7F2 intensities in APTES/TEOS hybrid NPs doped with [Ln(acac)33H2O] (Ln 1⁄4 Eu, Tb) complexes (315 nm excitation). The intensities were normalized to the corresponding values at 10 K. (B) The linear dependence of ln(D) (sym- bols) with 1/T above 175 K follows the equation ln(D) 1⁄4 105.2/T + 0.8 (r2 > 0.997, straight line). Adapted with permission from Brites, C.D.S., Lima, P.P., Silva, N.J.O., Milla ́n, A., Amaral, V.S., Palacio, F., Carlos, L.D. 2013b. Ratiometric highly sensitive luminescent nanothermometers working in the room temperature range. Applications to heat propagation in nanofluids. Nano- scale 5, 7572–7580. © 2013 The Royal Society of Chemistry.PDF Image | HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS
PDF Search Title:
HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHSOriginal File Name Searched:
Chemistry-Rare-Earths-49.pdfDIY PDF Search: Google It | Yahoo | Bing
Sulfur Deposition on Carbon Nanofibers using Supercritical CO2 Sulfur Deposition on Carbon Nanofibers using Supercritical CO2. Gamma sulfur also known as mother of pearl sulfur and nacreous sulfur... More Info
CO2 Organic Rankine Cycle Experimenter Platform The supercritical CO2 phase change system is both a heat pump and organic rankine cycle which can be used for those purposes and as a supercritical extractor for advanced subcritical and supercritical extraction technology. Uses include producing nanoparticles, precious metal CO2 extraction, lithium battery recycling, and other applications... More Info
| CONTACT TEL: 608-238-6001 Email: greg@infinityturbine.com | RSS | AMP |