A HTO‐Type Nonlinear Optical Fluorophosphate with Ultrawide Bandgap

Abstract

Compounds having hexagonal tungsten oxides (HTO) topology are of intense research interests owing to their potential functional properties, such as nonlinear optical (NLO) performances. However, most of the reported HTO‐type compounds exhibit narrow optical bandgaps because of the d–d electronic transition of compositional d⁰ transition metals and lone pair electrons effect of Se⁴⁺/Te⁴⁺, which hinder their applications in the high‐energy field, such as deep‐ultraviolet (deep‐UV) region. In this work, a new fluorophosphate, (NH₄)₃[Sc₃F₅(PO₄)](PO₃F)₂ exhibiting HTO‐topological structures is reported. Remarkably, the compound shows an ultrawide optical bandgap (E_g(exp.) > 6.2 eV, E_g(cal.) = 6.724 eV), surpassing those of reported HTO‐type compounds. The fact is mainly ascribed to the collaborative effect of Sc³⁺ without destructive d–d transition, the PO₄ and PO₃F units having large LUMO‐HOMO gaps. Furthermore, it exhibits a phase‐matchable second‐harmonic generation (SHG) response of ca. 0.65 × KDP, underscoring its potential use for NLO applications. This work provides new opportunities for discovering HTO‐type NLO crystals with ultrawide bandgaps.