Research advances of novel nonlinear optical crystals based on second-order Jahn-Teller effects(SOJT)

Explorations of new inorganic second-order nonlinear optical(NLO) materials is one of the current frontier topics due to their optoelectronics application such as frequency shifting,optical modulating,telecommunications and signal processing.Since 1998,a series of noncentrosymmetric(NCS) and polar oxides containing cations susceptible to second-order Jahn-Teller(SOJT) distortions,specifically,octahedrally coordinated d0 transition metals(TMs: Mo6+,W6+,V5+,and Nb5+.) and cations with stereo-chemically active lone pairs(SCALP,I5+,Te4+,Se4+,and Sn2+.),were successfully synthesized.Many of these materials exhibit large powder second-harmonic generation(SHG) efficiencies( 400×α-SiO2).This paper reviewed the progress on materials of the past decade,including the search for new materials and crystal growth.The materials were divided into three categories: NCS oxides containing one kind of SOJT cations(d0 or SCALP),NCS oxides containing both kinds of SOJT cations,and NCS oxides containing SOJT cations and other NCS building units such as borate π-orbital systems,tetrahedral groups and d10 transition metal cations(Zn2+,Cd2+,and Sn4+.).