The First UV Nonlinear Optical Selenite Material: Fluorination Control in CaYF(SeO 3 ) 2 and Y 3 F(SeO 3 ) 4 .

It is a great challenge to develop UV nonlinear optical (NLO) material due to the demanding conditions of strong second harmonic generation (SHG) intensity and wide band gap. The first ultraviolet NLO selenite material, Y 3 F(SeO 3 ) 4 , has been obtained by control of the fluorine content in a centrosymmetric CaYF(SeO 3 ) 2 . The two new compounds represent similar 3D structures composed of 3D yttrium open frameworks strengthened by selenite groups. CaYF(SeO 3 ) 2 has a large birefringence (0.138@532 nm and 0.127@1064 nm) and a wide optical band gap (5.06 eV). The non-centrosymmetric Y 3 F(SeO 3 ) 4 can exhibit strong SHG intensity (5.5×KDP@1064 nm), wide band gap (5.03 eV), short UV cut-off edge (204 nm) and high thermal stability (690 °C). So, Y 3 F(SeO 3 ) 4 is a new UV NLO material with excellent comprehensive properties. Our work shows that it is an effective method to develop new UV NLO selenite material by fluorination control of the centrosymmetric compounds.