Experimental observation of the nonadditivity of various mechanisms of population inversion of the 4I11/2→4I13/2 transition of the Er3+ ion in a YSGG:Cr3+:Er3+ crystal

Experimental investigations were made of the threshold pump energy of a YSGG:Cr³⁺:Er³⁺ crystal as a function of the filtering wavelength of the pump radiation and the concentration of erbium ions. The contributions of two mechanisms of erbium ion excitation to population inversion of the ⁴I_11/2 → ⁴I_13/2 Er³⁺ transition in a YSGG:Cr³⁺:Er³⁺ crystal were nonadditive, as predicted previously. These mechanisms involved Cr→Er energy transfer and cross-relaxational depletion of the ⁴S_3/2 state of Er³⁺.