Second-Order Nonlinear Optical Materials Based on Metal Iodates, Selenites, and Tellurites

In this chapter, the syntheses, structures, and Second Harmonic Generation (SHG) properties of metal iodates, selenites, and tellurites all of which contain a lone pair cation in an asymmetric coordination geometry were reviewed. A second asymmetric building unit such as distorted octahedra of the d⁰ transition-metal (TM) cations such as V⁵⁺, Mo⁶⁺, other cations with a stereochemically active lone pair such as Pb²⁺ and Bi³⁺, and tetrahedral groups such as BO ₄ ⁵⁻ and PO ₄ ³⁻ , can be introduced into metal iodates, selenites, and tellurites. The combination of d⁰ transition-metal cations with the iodate groups afforded a large number of new metal iodates, a number of which display excellent SHG properties due to the additive effects of polarizations from both types of the asymmetric units. Introducing other lone-pair cations such as Pb²⁺ and Bi³⁺ into the metal iodates is also an effective strategy to design new SHG materials. With respect to the metal selenite or tellurite systems, many compounds in the alkali or alkaline earth-d⁰ TM–Se(IV)/Te(IV)–O systems can also exhibit excellent SHG properties due to the additive effects of polarizations from both types of asymmetric units. Lanthanide or posttransition metal main group element-d⁰ TM–Se(IV)/Te(IV)–O compounds are usually structurally centrosymmetric and not SHG active, but they can also display abundant structural diversities and interesting magnetic or luminescent properties. Metal tellurites and selenites containing tetrahedral groups of the main group elements such as BO₄ and PO₄ may also form NCS structures with excellent SHG properties.