Rb21.89W32.66O108: An Excellent Mid- and Far-IR Nonlinear-Optical Material with a Wide Band Gap.

IR nonlinear-optical (NLO) crystal is the important device in IR laser technology. Nevertheless, the application of most IR NLO crystals in high-power lasers is always limited by the low laser damage threshold (LDT), which is mainly caused by the narrow optical band gap (Eg). Here, the physical properties of the Rb21.89W32.66O108 (RWO) crystal with a longer absorption cutoff edge and a wide Eg were systematically studied for the first time. A preliminary measurement of the LDT was performed, and the result shows that RWO has a high powder LDT of about 42 times that of AgGaS2. In order to better understand the relationship between the structure and properties, the dipole moments of WO6 octahedra were accurately calculated and analyzed. Meanwhile, it was indicated that RWO exhibits an ideal frequency doubling strength with the type I phase matching. Finally, it was revealed that RWO has great application value as an IR NLO crystal.