Radiative recombination rate Χ as functions of the energy gap E_ai and absorbed photon wavelength λ between the levels |a_i〉_{i = 1,2} and |b〉. It takes the parameters γ₁ = 1.5γ, γ₂ = 0.5γ₁, p₁ = p₂ = 0.35, Γ_c = 4.5γ₁, E_cv = 1.05 eV. The other parameters are the same as those in Fig. 3.