The Yb3+ ion exhibits a small quantum defect and a quasi-three level system with a long upper laser level lifetime (around 1 ms for Yb:YAG), which is important for energy accumulation in Q-switched lasers. The wide luminescence band of Yb3+ is advantageous for the generation of sub-picosecond pulses. Yb3+ doped crystals do not suffer from luminescence concentration quenching. Their long energy storage lifetime, broad absorption band at 940 nm and very low quantum defect make Yb:YAG and Yb:LuAG crystals superior candidates for diode-pumped high-energy lasers.