Ca3(TeO3)2(MO4) (M = Mo, W): Mid-Infrared Nonlinear Optical Tellurates with Ultrawide Transparency Ranges and Superhigh Laser-Induced Damage Thresholds

Intense interests in mid-infrared (MIR) nonlinear optical (NLO) crystals have erupted in recent years due to the development of optoelectronic applications ranging from remote monitoring to molecular spectroscopy. Here, two polar crystals Ca₃(TeO₃)₂(MO₄) (M = Mo, W) were grown from TeO₂-MO₃ flux by high-temperature solution methods. Ca₃(TeO₃)₂(MoO₄) and Ca₃(TeO₃)₂(WO₄) are isostructural, which feature novel structures consisting of asymmetric MO₄ tetrahedra and TeO₃ trigonal pyramids. Optical characterizations show that both crystals display ultrawide transparency ranges (279 nm to 5.78 μm and 290 nm to 5.62 μm), especially high optical transmittance over 80% in the important atmospheric transparent window of 3-5 μm, and superhigh laser damage thresholds (1.63 GW/cm² and 1.50 GW/cm²), 54.3 and 50 times larger than that of state-of-the-art MIR NLO AgGaS₂, respectively. Notably, they exhibit the widest band gaps and the loftiest laser-induced threshold damages among the reported tellurates so far. Moreover, Ca₃(TeO₃)₂(MO₄) exhibit type I phase matching at two working wavelengths owing to their large birefringence and strong second-harmonic generation responses from the distorted anions, as further elucidated by the first-principles calculations. The above characteristics indicate that Ca₃(TeO₃)₂(MO₄) crystals are high-performance MIR NLO materials, especially applying in high-power MIR laser operations.