The multiphoton ultraviolet and visible upconversion luminescence of ZBLAN material

The multiphoton ultraviolet and visible upconversion luminescence of Tm3+Yb3+ codoped ZBLAN fluoride glass as excited by a 975nm diode laser was studied. Two typical ultraviolet 290.6nm 1I6 &rarr 3H6 and 362.0nm 1D2 &rarr 3H6 upconversion luminescence lines were found. The careful measurement of the variation of upconversion luminescence intensity F as a function of the 975nm pumping laser power P has proven that the 290.6nm 1I6 &rarr 3H6 and 362.0nm 1D2 &rarr 3H6 upconversion luminescences are a six-photon and a five-photon upconversion luminescence respectively. Several visible upconversion luminescence lines at 450.5nm, 473.9nm, 648.5nm, (687.3nm, 696.2nm) and (793.5nm, 800.7nm) were found also, which result from the fluorescence transitions of 1D2 &rarr3F4, 1G4&rarr3H6, 1G 4&rarr3F4, 3F3&rarr 3H6 and 3H4&rarr3H 6 of Tm3+ ion respectively. It has been proved that the upconversion luminescence of 1G4 state is a three-photon upconversion process, while that of 3F3 or 3H4 state is a two-photon upconversion process. The theoretical analysis suggests that the upconversion mechanism of the 362.0nm 1D2 &rarr3H6 upconversion luminescence is the cross energy transfer of {3H4(Tm 3+)&rarr3F4(Tm3+), 1G4(Tm3+)&rarr1D 2(Tm3+)} and {1G4(Tm 3+)&rarr3F4(Tm3+), 3H4(Tm3+)&rarr1D 2(Tm3+)} between Tm3+ ions, whereas the mechanism of the 290.6nm 1I6 &rarr 3H 6 upconversion luminescence is the sequential energy transfer of {2F5/2(Yb3+)&rarr2F 7/2(Yb3+), 1D2(Tm 3+)&rarr3P1(Tm3+)} and { 2F5/2(Yb3+)&rarr2F 7/2(Yb3+), 1D2(Tm 3+)&rarr3P2(Tm3+)} from Yb 3+ ions to Tm3+ ions. In addition, the upconversion luminescence of 1G4 and 3H4 state also results from the sequential energy transfer {2F 5/2(Yb3+)&rarr2F7/2(Yb 3+), 3H4(Tm3+) &rarr1G4(Tm3+)} and {2F 5/2(Yb3+)&rarr2F7/2(Yb 3+), 3F4(Tm3+) &rarr3F2(Tm3+)} from Yb3+ ions to Tm3+ ions respectively.EI