Energy transfer between managanese(II) and erbium(III) in various fluoride glasses

The fluorescence spectra and lifetimes of fluoride glasses of molar composition 36PbF₂, 24MnF₂ (or ZnF₂), 35GaF₃, 5 (or 7) Al(PO₃)₃, doped by ErF₃ were investigated. The emission of Mn(II) in absence of Er(III) consists of a broad band centered around 630 nm and an integrated lifetime of 1.4 msec. In the presence of Er(III) the intensity and lifetimes are decreased as a result of energy transfer to the ⁴F _{9 2} level of Er(III). The fluorescence of Er(III) arising from ⁴S _{3 2} at 543 nm has an integrated lifetime of 0.06 ms in the absence of Mn(II) and is decreased to 0.01 ms in the presence of Mn(II) as a result of energy transfer to Mn(II). The 666-nm luminescence of Er(III) due to ⁴F _{9 2} emission under excitation at 370 nm (⁴G _{11 2}) is about 20 times weaker than the 543-nm emission when Mn(II) is absent. However, in the presence of Mn(II) this emission becomes 5 times stronger than the 543-nm emission. This intensified emission has a non-exponential time dependence. The longer component corresponds to the transfer of stored energy in Mn(II) to Er(III) while the short-lived component is probably due to cascading down Er(III) → Mn(II) → Er(III) through states above the Stokes threshold of Mn(II). This interpretation is backed up by weaker 543-nm emission and stronger 630-nm broad-band emission when the mixed system is excited in one of the upper excited states, of Mn(II) at 395 nm, or of Er(III).