Energy transfer between Gd³⁺ and Sm³⁺ the effect of Gd³⁺ on quenching of Sm³⁺ and intensity parameters of Sm³⁺ in borate glasses

Intensity parameters of Sm³⁺ in borate glasses were obtained by fitting the oscillator strengths to the Judd-Ofelt formula and a study of energy transfer from gadolinium to samarium was performed. An increase of samarium fluorescence originating from the ⁴G _{5 2} level was observed in the presence of gadolinium, in the concentration range of 0.1-3 wt% samarium with gadolinium constant at 3 wt%. The intensity of samarium fluorescence on excitation at 273 nm increased by one order of magnitude in the presence of gadolinium. From the excitation spectrum of the double-doped glasses (Gd + Sm), it was deduced that energy absorbed by gadolinium is transferred from ⁶P _{7 2} gadolinium levels to the ⁴P _{3 2} and ⁴P _{5 2} samarium levels. The mechanism of this energy transfer was obtained by plotting the energy transfer probabilities as a function of samarium concentration. A linear dependence of η₀ η (η intensity of gadolinium in the presence of samarium) versus square of concentration of Sm + Gd is obtained. From this it is concluded that the transfer is of electric-multipolar type, mainly dipole-dipole. A small increase (about 10%) of fluorescence of samarium in the presence of gadolinium excited at levels where no energy transfer can take place is attributed to the fact that the quenching of samarium occurring by the cross relaxation (⁴G _{5 2} → ⁶F _{9 2}) (⁶H _{5 2} → ⁶F _{9 2}) is suppressed by the presence of gadolinium as seen from concentration dependence of samarium doped glasses compared to double-doped glasses.