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

A full-scale compositional analysis of Yb3+-doped heavy metal fluoride glas ses (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+ F-2(5/2) manifold, followed by a thermally-driven population redistribution to highe r levels within the manifold, net cooling can be achieved by anti-Stokes fl uorescence back to the ground state. This paper reports on fluoride glasses in the ZBLAN and BaF2-InF3-GaF3 (BIG) families which have shown promise fo r fluorescent cooling. ZBLANPb:Yb3+ is the first solid to actually exhibit net cooling due to anti-Stokes fluorescence. The BIG-derived hosts have bee n determined to contain similar mean emission photon energies and larger lo ng-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 ZBLAN Pb at temperatures below 80 K and may attain a minimum temperature of 45 K compared to 55 K expected for the ZBLANPb. (C) 1999 Elsevier Science B.V. A ll rights reserved.