Near-Infrared Phosphorescent Hybrid Organic-Inorganic Perovskite with High-Contrast Dielectric and Third-Order Nonlinear Optical Switching Functionalities.

Hybrid organic-inorganic perovskites providing integrated functionalities for multimodal switching applications are widely sought-after materials for optoelectronics. Here, we embark on a study of a novel pyrrolidinium-based cyanide perovskite of formula (CHN)KCr(CN), which displays thermally driven bimodal switching characteristics associated with an order-disorder phase transition. Dielectric switching combines two features important from an application standpoint: high permittivity contrast (Δε' = 38.5) and very low dielectric losses. Third-order nonlinear optical switching takes advantage of third-harmonic generation (THG) bistability, thus far unprecedented for perovskites and coordination polymers. Structurally, (CHN)KCr(CN) stands out as the first example of a three-dimensional stable perovskite among formate-, azide-, and cyanide-based metal-organic frameworks comprising large pyrrolidinium cations. Its stability, reflected also in robust switching characteristics, has been tracked down to the Cr component, the ionic radius of which provides a large enough metal-cyanide cage for the pyrrolidinium cargo. While the presence of polar pyrrolidinium cations leads to excellent switchable dielectric properties, the presence of Cr is also responsible for efficient phosphorescence, which is remarkably shifted to the near-infrared region (770 to 880 nm). The presence of Cr was also found indispensable to the THG switching functionality. It is also found that a closely related cobalt-based analogue doped with Cr ions displays distinct near-infrared phosphorescence as well. Thus, doping with Cr ions is an effective strategy to introduce phosphorescence as an additional functional property into the family of cobalt-cyanide thermally switchable dielectrics.