Toni Riedener and Hans U. Güdel
Upconversion dynamics of Er³⁺ doped RbGd₂Br₇
J. Chem. Phys. 107, 2169-2174 (1997)                 

Abstract: NIR-to-VIS upconversion mechanisms upon excitation into ⁴I_11/2 around 980 nm in the Er³⁺ doped low energy phonon host material RbGd₂Br₇ are identified and analyzed. The small energy difference between the first excitation step ⁴I_15/2 ⁴I_11/2 and the second step ⁴I_11/2 ⁴F_7/2 leads to a competitive situation of excited state absorption and energy transfer upconversion processes. Their relative efficiency strongly depends on the excitation energy and temperature. Fingerprinting techniques based on the temporal evolution of the upconverted luminescence after a 10 ns laser pulse are used to distinguish the two mechanisms. Rate constants for the relevant processes are determined. With W_t = 68 s^–1 at 10 K the energy transfer step in the upconversion process is comparable to Er³⁺ doped CsCdBr₃.