Without the purge, the 4,300-nm fluorescence emitted by the diode-pumped crystal is completely absorbed by atmospheric CO2. In effect, the experimental setup functioned as a very sensitive atmospheric CO2 detector. Conclusions This paper discussed two applications of Tm3+ sensitization of rare earth-doped low phonon energy host crystals, in which the resulting reduction in multi-phonon relaxation rates enables useful energy transfer processes to occur that are quenched in conventional oxide and fluoride crystals. One application is the enabling of an endothermic cross-relaxation process for Tm3+ that converts lattice phonons to infrared
emission GSK872 solubility dmso near 1,200 nm. The existence of this process suggests that endothermic phonon-assisted energy transfer could be a fundamentally new way of achieving optical cooling in a solid. The other application is a novel optically pumped mid-IR LY2874455 price phosphor that converts 805-nm light from readily available low-cost diodes into broadband emission from 4 to 5.5 μm. The phosphor is efficient, low-cost, and scalable. Application of theories for electric dipole-dipole sensitizer-acceptor GDC-0941 concentration interactions shows that the critical radii for energy transfer processes between
rare earth ions do not change significantly between various host crystals. The novel energy transfer processes observed in low phonon energy host crystals occur because the multi-phonon relaxation rates for the levels involved are reduced and no longer compete with the radiative and non-radiative energy transfer rates. In imagining new kinds of applications for low phonon energy crystals, circumstances in which the multi-phonon relaxation rates can be reduced to much less than the known rates for electric dipole interactions should be investigated. Acknowledgements Work at Loyola University Maryland was supported by the National Science Foundation Division of Electrical and Communication Systems under grants ECS-9970055 and ECS-0245455. The Office of Naval Research supported this work
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