Energy transfer up-conversion in Tm3+-doped silica fiber

A study of the mechanisms responsible for the infra-red to near infra-red up-conversion in thulium doped silica fibres is presented. Up-conversion luminescence was observed from the H4 level of Tm under 1586 nm pumping into the F4 level. The quadratic dependence of the up-conversion luminescence at 800 nm on the 1800 nm luminescence from the F4 level confirms that the H4 level is populated by a two photon process. Two possible processes are proposed as mechanisms responsible for the up-conversion: excited state absorption and energy transfer up-conversion. The decay characteristics of the luminescence from the H4 level were studied under direct and indirect pumping at 786 and 1586 nm, respectively. By comparing the decay waveforms to the solution of a simple set of rate equations, the energy transfer upconversion process (F4,F4→H4,H6) is established at Tm2O3 concentrations greater than 35 ppm mol. PACS codes: 31.70.Hq; 32.70.Cs; 33.50.-j Manuscript with Figures and tables