The study of structure evolvement of KTiOPO4 family and their nonlinear optical properties

Nonlinear optical (NLO) crystal materials greatly expand the tunable range of the lasers via frequency conversion and promote the rapid development of laser technology. Recently, compared to traditional time-consuming “trial-and-error” method, chemical substitution-oriented design has been proven to be effective in exploring novel NLO materials with excellent performance. KTiOPO4 (KTP) is a famous commercial crystal material in visible region owing to its large NLO coefficient, wide acceptance angle and phase-matching behavior. Especially, KTP possesses an adaptable framework structure, which is a good structure prototype for chemical substitution-oriented design. When choosing KTP as the matrix, >120 KTP family members have been discovered. Moreover recently the research system has been extended to sulfates with enlarged band gap, which opens the door to explore excellent KTP-type NLO materials for UV application. Based on the summary of the existing reports, this article summarizes almost all the KTP-type compounds especially new members discovered in this century for the first time, and elaborates on structure evolvement of KTP family and their NLO properties. We classify the whole KTP-family materials according to valence of the anion groups as PO43−/AsO43−/(PxAs1−x)O43−, SiO44−/GeO44−, SO42− and further discuss the relationships between microscopic structures and NLO properties. And we believe this review will shed helpful insights on effective designing of novel functional materials.