We have studied the flourescence characteristics of Ho 3+ and Tm 3+ in ErAlG:Ho, Tm and investigated the Er ↔ Ho and Er ↔ Tm energy transfer present in this system. In the infrared, the crystal ErAlG:Ho, Tm presents three groups of sharp lines (centered at ∼18 000, ∼19 300, and ∼21 000 Å), whose intensities are strongly temperature-dependent. The first two groups are attributable to the Tm 3H 4 → 3H 6 transition, while the third group represents the Ho 5I 7 → 5I 8 transition. In YAlG:Er (50%), Ho(2%), only the Ho emission centered at ∼21 000 Å is observed in the infrared. Under pulsed excitation, the emissions at ∼17 900, ∼19 000, and ∼21 000 Å in ErAlG:Ho, Tm present a double exponential decay; the time dependences of the decays of the first two emissions are essentially the same; however, the 19 000 and 21 000 Å emissions present different decay patterns. In YAlG:Er (50%), Ho (2%), on the other hand, the decay of the 21 000 Å emission is purely exponential at all temperatures studied. The above results for ErAlG:Ho, Tm are explained by means of a rate-equation model in which the Ho → Er and Tm → Er transfer are treated as activation-type processes which effect a coupling between (1) the Ho and Tm ions, and (2) the Ho or Tm ions and quenching impurities.