Figure 5 shows an overlay of the temperature-dependent rate modelling with the temperature-dependent intensity data from Figure 4[33]. The model predicts the observed increase in emission from the 3H5 level as the temperature is raised. The model shows that the branching ratio for the 3H4 to 3H5 Selleckchem Poziotinib transition is less than 1%, and as a result, the population of the 3H5 arises almost entirely from the C2 cross-relaxation process [33]. Between 300 and 400 K the model also predicts the observation that the emission from the 3F4 and 3H4 levels is unchanged as the temperature rises

because multi-phonon relaxation has not increased to a level that it competes with radiation and cross-relaxation. Figure 5 Temperature dependence of infrared fluorescence from Tm 3+ :YCl 3 . Overlay of temperature-dependent selleck inhibitor rate model for the relative population of the three lower levels for Tm3+:YCl3 with the temperature-dependent intensity data from Figure 4. The solid lines are the model, and the markers are the data. The population of the 3F4 level at 300 K is normalized to 1. The sample has a Tm3+ concentration of 0.7 × 1020 ions/cm3. This result is significant because it implies that the process C2 converts lattice phonons into 1,200-nm radiation, which is a cooling effect. In contrast to previous demonstrations of solid-state optical cooling from anti-Stokes emission

[37–43], cooling from cross-relaxation will not lose efficiency at low temperatures because the -641 cm-1 energy gap for the process is temperature Osimertinib independent. At low-temperatures, cooling from anti-Stokes emission loses efficiency because of thermal depopulation of the upper Stark levels. Also of interest for Tm3+:YCl3 is that additional study of the concentration dependence of the cross-relaxation rates determined that the critical radius R cr at room temperature for

the energy transfer is about 15 Å. That distance is comparable to R cr for Tm3+ cross-relaxation in conventional oxide and fluoride hosts [7, 8]. This implies that the endothermic cross-relaxation process C2 is enabled by the reduction in multi-phonon quenching and not because interaction rates between neighbouring Tm3+ ions are changed significantly by a chloride host. These spectroscopic results suggest that a heat generation study should be conducted for the near-IR-pumped Tm3+ in a low phonon energy host. Energy transfer in Tm3+-Pr3+ co-doped crystals In addition to its own IR-emitting properties, the Tm3+ ion has been used to sensitize other rare earth ions for diode pumping. Most notable is the Ho3+ ion, which has a useful IR laser transition at 2.1 μm from its first excited state to its ground state but lacks a level that absorbs at 800 nm. Energy transfer from Tm3+ to Ho3+ has been used to create diode-pumped 2.1-μm lasers using YLF [7] and YAG [8] host crystals. Tm3+ Selleck PI3K Inhibitor Library sensitization has also been used in low phonon energy crystals.