Investigation of the spectroscopic properties and laser performance of rare earth and transition metal ions doped crystals (garnets) is presented. Recent spectroscopic results of energy transfer and back transfer mechanism in Cr:Tm:Ho:YAG, Cr:Tm:Ho:LuAG (Lu3Al5O12) at a variety of temperatures (10K-300K) will be reported. A direct energy transfer from Tm3+ excited states to Ho3+ 5I7 lasing level was observed and analyzed. Multipolar interaction between special sites of Cr3+ and rare earth lasing ions (Tm3+, Ho3+), which results from a strong correlation placement distribution was found and analyzed. The effect of this interaction on the enhancement of laser efficiency will be discussed. The room temperature performance and the laser parameters of broadly tunable solid state lasers (at 1150-1600 nm), based on Cr4+ doped different garnets will be presented and discussed as well.