The characteristic saturation phenomenon of upconversion luminescence in holmium–ytterbium-co-doped oxyfluoride glass Ho(0.1)Yb(5):FOG

The upconversion luminescence of holmium Ho3+ ion sensitized by ytterbium Yb3+ ion in Ho3+Yb3+-co-doped oxyfluoride glass Ho(0.1)Yb(5):FOG is investigated in this paper. A plenty of upconversion luminescence lines are measured out. The upconversion mechanism of Ho(0.1)Yb(5):FOG, when excited by 960 nm laser, is the energy transfer from Yb3+ to Ho3+ ion. A very weak 795.5 nm common photoemission fluorescence is detected, which is recognized as the 5I4→5I8 fluorescence transition based on careful measurement, calculation and analysis. And moreover, a novel characteristic upconversion luminescence saturation phenomenon is found. It is that the log F–log P curve of upconversion fluorescence vs. pumping laser power is a straight line, and meanwhile the slopes of these double-logarithmic F–P plots are smaller than normal multi-photon relation clearly. When pumping laser spot is increased, the slopes of these double logarithmic F–P plots could be enhanced noticeably from small value to near the normal multi-photon relation value. The mechanism of this characteristic saturation phenomenon is the energy expansion resulted from energy resonant migration among Yb3+ ions.