Upconversion mechanisms in an erbium-doped transparent glass ceramic

Upconversion fluorescence in an erbium-doped transparent oxyfluoride glass ceramic is studied by use of fluorescence decays and time-dependent fluorescence and excitation spectra. Sequential two-photon absorption upconversion and energy transfer upconversion are reported, and their origins are identified. Sequential two-photon absorption upconversion is produced primarily in the glass phase, and energy transfer upconversion originates exclusively in the crystalline phase.