Quantum counter action has been demonstrated at 10 &mgr;m. A LaBr3:Sm crystal shows a detectivity of 6.7×107cm Hz1/2/W in the 9.6–10.3 &mgr;m region. The same crystal system is also sensitive to infrared radiation in several other bands between 2 and 10 &mgr;. The relative sensitivity for different wavelengths is in agreement with the absorption strengths of the samarium transitions involved. By using a single laser pump line but switching input filters this multicolor sensitivity was used to determine the temperature of the blackbody target used. At very high pump powers there is a large increase in fluorescence output. This output is the result of a ‘‘photon avalanche’’ effect similar to that recently discovered in LaBr3:Pr. The slow buildup and rapid decay of this output provides strong evidence that a multi‐ion process is involved.