Compositional dependence of up-conversion process in Tm3+-Yb3+ codoped oxyfluoride glasses and glass-ceramics

Up-conversion of infrared radiation to the visible and ultraviolet regions in PbF2-GeO2-Al2O3 -Tm2O3-Yb2O3 oxyfluoride glasses and glass ceramics was obtained, exciting at 1.0 mum with a diode laser at room temperature. Transparent films and microspheres were prepared by a modified spin-coating technique. The effect of host composition on the up-conversion luminescence was studied in order to improve the ultraviolet radiation generation. In the glass samples, the Tm3+ blue (4786 Angstrom) and red (6500 Angstrom) visible emissions got more intense as the PbF2 content was increased. The main Tm3+ blue emission (4786 Angstrom,(1)G(4)--> H-3(6)), results from a three-photon process. A second blue emission (4500 Angstrom, D-1(2)--> F-3(4)), followed by a UV emission (3650 and 3850 Angstrom, D-1(4)--> H-3(6)) was observed in the (2PbF(2)/GeO2) glass ceramics, in a narrow range of Al2O3 concentration. The D-1(2) level of the Tm3+ ions is populated by a fourth photon from the cross-relaxation process given by (F-3(4), (1)G(4))-->(H-3(6),D-1(2)). (C) 2001 Elsevier Science B.V. All rights reserved.