Compositional investigation of Yb3+-doped heavy metal fluoride glasses for laser-induced fluorescent cooling applications

A full-scale compositional analysis of Yb3+-doped heavy metal fluoride glasses (HMFG) has been undertaken to determine potential hosts for use in the development of a first-generation optical cryocooler for space-borne remote sensing applications. By pumping to the lower levels of the Yb3+ 2F5/2 manifold, followed by a thermally-driven population redistribution to higher levels within the manifold, net cooling can be achieved by anti-Stokes fluorescence back to the ground state. This paper reports on fluoride glasses in the ZBLAN and BaF2-InF3-GaF3 (BIG) families which have shown promise for fluorescent cooling. ZBLANPb:Yb3+ is the first solid to actually exhibit net cooling due to anti-Stokes fluorescence. The BIG-derived hosts have been determined to contain similar mean emission photon energies and larger long-wavelength absorption tails than those of ZBLANPb:Yb3+. Low-temperature absorption and fluorescence spectra have indicated that the Yb3+-containing BIG glasses should have a cooling efficiency more than twice that of ZBLANPb at temperatures below 80 K and may attain a minimum temperature of 45 K compared to 55 K expected for the ZBLANPb.