Energy transfer (ET) and heat generation processes in Yb 3 ∕Ho 3 -codoped low-silica calcium aluminosilicate glasses were investigated using thermal lens (TL) and photoluminescence measurements looking for the emission around 2.0 μm. Stepwise ET processes from Yb 3 to Ho 3 , upon excitation at 0.976 μm, produced highly efficient emission in the mid-infrared range at around 2.0 μm, with high fluorescence quantum efficiency (η 1 ∼ 0.85 and independent of Ho 3 concentration) and relatively very low thermal loading (<0.4) for concentration up to 1.5% of Ho 2 O 3 . An equation was deduced for the description of the TL results that provided the absolute value of η 1 and the number of emitted photons at 2.0 μm per absorbed pump photon by the Yb 3 ions, the latter reaching 60% for the highest Ho 3 concentration. These results suggest that the studied codoped system would be a promising candidate for the construction of photonic devices, especially for medical applications.