This paper presents a detailed analysis of the optical and the dielectric properties of ZnGeP2 crystals in middle IR and far IR spectral ranges and also the first experimental results on 1-W 102 similar to 110-mu m radiation generation by means of difference frequency generation of CO2 laser line pairs. It is shown that the MW (peak power) level is achievable now and AgIn0.35Ga0.65Se2 crystals have to be investigated in details as a potential crystals for efficient generation of FIR radiation.