One of the promising ways to improve the efficiency of lasers operating at wavelengths near 1600 nm and 3000 nm on base of garnets doped with Er3+ ions is their sensitization with Ce3+ ions. In this work the investigation results of spectral characteristics of YAG:Er3+, YAG:Ce3+ and YAG:Ce3+, Er3+ crystals at room temperatures are presented. Dependencies of these characteristics on the optical excitations at 457 nm, 808 nm and 980 nm wavelengths are studied. The influence of Ce3+ sensitizer ions on the efficiency and mechanisms of the various energy levels' population processes of Er3+activator ions in the YAG matrix is discussed.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.