  We have studied the cathodo- and radioluminescence of Nd:YAG and of Tm:YAG
single crystals in an extended wavelength range up to $\approx 5\,\mu$m in view
of developing a new kind of detector for low-energy, low-rate energy deposition
events. Whereas the light yield in the visible range is as large as $\approx
10^{4}\,$photons/MeV, in good agreement with literature results, in the
infrared range we have found a light yield $\approx 5\times
10^{4}\,$photons/MeV, thereby proving that ionizing radiation is particularly
efficient in populating the low lying levels of rare earth doped crystals.
