Spectroscopic properties and mechanisms of excited state absorption and energy transfer upconversion for Er3+-doped glasses

The upconversion fluorescences near 0.55 and 0.66 μm and Stokes fluorescences near 0.98 and 2.72 μm were measured for Er3+-doped aluminate, gallate and several other glasses under infrared ation into the 4I92 level. It was found that the quantum efficiencies of emissions from a given level, except the 4I132 level, increased in the order of decreasing phonon energies of the glass hosts. The fluorescence originating from the 4I132 level and its quantum efficiency are not dependent upon the phonon energies of glass hosts, due to influences of the energy transfer upconversion and excited state absorption from the 4I132 level. Moreover this fluorescence is closely related to the 4I112 lifetimes, in which the stronger fluorescence can be observed in a glass which has a shorter 4I112 lifetime. The green upconversion fluorescence originating from the 4S32 level mainly results from the excited state absorption from the 4I132 level and the red upconversion fluorescence coming from the 4I92 level mainly generates from the energy transfer upconversion through the 4I132 level for Er3+-doped aluminate and gallate glasses.