The multiphoton ultraviolet and visible upconversion luminescence of ZBLAN material

摘要

The multiphoton ultraviolet and visible upconversion luminescence of Tm~(3+)Yb~(3+) codoped ZBLAN fluoride glass as excited by a 975nm diode laser was studied. Two typical ultraviolet 290.6nm ~1I_6 → ~3H_6 and 362.0nm ~1D_2 → ~3H_6 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 ~1I_6 → ~3H_6 and 362.0nm ~1D_2 →~3H_6 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 ~1D_2 →~3F_4, ~1G_4→~3H_6,~1G_4→~3F_4,~3F_3→~3H_6 and ~3H_4→~3H_6 of Tm~(3+) ion respectively. It has been proved that the upconversion luminescence of ~1G_4 state is a three-photon upconversion process, while that of ~3F_3 or~ 3H_4 state is a two-photon upconversion process. The theoretical analysis suggests that the upconversion mechanism of the 362.0nm ~1D_2→~3H_6 upconversion luminescence is the cross energy transfer of {~3H_4(Tm~(3+))→~3F_4(Tm~(3+)), ~1G_4(Tm~(3+))→~1D_2(Tm~(3+))} and {~1G_4(Tm~(3+))→~3F_4(Tm~(3+)), ~3H_4(Tm~(3+))→~1D_2(Tm~(3+))} between Tm~(3+) ions, whereas the mechanism of the 290.6nm ~1I_6→~ 3H_6 upconversion luminescence is the sequential energy transfer of {~2F_(5/2)(Yb~(3+))→~2F_(7/2)(Yb~(3+)), ~1D_2(Tm~(3+))→~3P_1(Tm~(3+))} and {~2F_(5/2)(Yb~(3+))→~2F(7/2)(Yb~(3+)), ~1D_2(Tm~(3+))→~3P_2(Tm~(3+))} from Yb~(3+) ions to Tm~(3+) ions. In addition, the upconversion luminescence of ~1G_4 and ~3H_4 state also results from the sequential energy transfer {~2F_(5/2)(Yb~(3+))→~2F_(7/2)(Yb~(3+)), ~3H_4(Tm~(3+))-VG_4(Tm~(3+))} and {~2F_(5/2)(Yb~(3+))→~2F_(7/2)(Yb~(3+)),~3F_4(Tm~(3+))→~3F_2(Tm~(3+))} from Yb~(3+) ions to Tm~(3+) ions respectively.