Multiphoton ultraviolet and visible upconversion luminescence of Tm3+Yb3+ co-doped oxyfluoride glass

The ultraviolet upconversion luminescence of Tm3+ ions sensitized by Yb3+ ions in oxyfluoride glass when excited by a 975 nm diode laser was studied in this paper. One typical ultraviolet upconversion luminescence lines positioned at 362.3 nm was found. It can be attributed to the five-photon upconversion luminescence transition of 1D2 → 3H6. Several visible upconversion luminescence lines at 451.1 nm, (477.9 nm, 462.5 nm), 648.7 nm, (680.5 nm, 699.5 nm) and (777.5 nm, 800.7 nm) were found also, which results from the fluorescence transitions of five-photon 1D2 → 3F4, three-photon 1G4 → 3H6, three-photon 1G4 → 3F4, two-photon 3F3 → 3H6 and two-photon 3H4 → 3H6 of Tm3+ ion, respectively. The theoretical analysis suggests that the upconversion mechanism of the 362.3 nm 1D2 → 3H6 upconversion luminescence is the cross energy transfer of {3H4(Tm3+) → 3F4(Tm3+), 1G4(Tm3+) → 1D2(Tm3+)} and {1G4(Tm3+) → 3F4(Tm3+), 3H4(Tm3+) → 1D2(Tm3+)} between Tm3+ ions. In addition, the upconversion luminescence of 1G4 and 3H4 state results from the sequential energy transfer {2F5/2(Yb3+) → 2F7/2(Yb3+), 3H4(Tm3+) → 1G4(Tm3+)} and {2F5/2(Yb3+) → 2F7/2(Yb3+), 3F4(Tm3+) → 3F2(Tm3+)} from Yb3+ ions to Tm3+ions, respectively.