Abstract:

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⁺,W^6+,V⁵⁺,Nb⁵⁺,etc.) and cations with stereochemically active lone pairs (SCALP, e.g. I⁵⁺, Te⁴⁺, Se⁴⁺, Sn²⁺, etc.), were successfully synthesized. Many of these materials exhibit large powder second-harmonic generation (SHG) efficiencies (> 400×α-SiO₂). This paper reviews the progress on the materials in the past decade, including the search for new materials and crystal growth. The materials are 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⁺, Sn⁴⁺, etc.).

Key words: second-order Jahn-Teller (SOJT) effect, noncentrosymmetric (NCS) structure, polar crystal, flux method, nonlinear optical (NLO) crystals