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 NCT-501 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 FRAX597 supplier radiation and cross-relaxation. Figure 5 Temperature dependence of infrared fluorescence from Tm 3+ :YCl 3 . Overlay of temperature-dependent selleck screening library 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 Florfenicol 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+ sensitization has also been used in low phonon energy crystals.