Helix-constructed polar rare-earth iodate fluoride as a laser nonlinear optical multifunctional material

The first trivalent rare-earth iodate fluoride nonlinear optical (NLO) crystal, Y(IO₃)₂F (YIF), was successfully designed and synthesized, featuring polarization-favorable helical chains constructed from trans-YO₆F₂ polyhedra and IO₃ groups. It exhibited a suitable balance of a wide transparency range of 0.26-10.0 μm, high laser damage threshold (LDT) of 39.6 × AgGaS₂, and moderate second harmonic generation (SHG) effect of 2 × KDP. A series of doped RE:YIF (RE = Pr, Nd, Dy, Ho, Er, Tm, and Yb) crystals were easily synthesized benefiting from the spring-shaped helix structure, which possess wide absorption and emission peaks as well as long lifetime, especially in the visible and near-infrared regions. Particularly, the remarkable fluorescence properties of Nd and Yb doped YIF crystals are comparable to and even better than those of traditional self-frequency doubling (SFD) crystals such as YAB, YCOB, and GdCOB. Thus, these RE-doped YIF crystals are promising laser SFD crystals. This work also indicated that constructing helical chains should be an effective strategy for the design of inorganic polar materials.