Designing a Beryllium-Free Deep-Ultraviolet Nonlinear Optical Material without a Structural Instability Problem

A beryllium-free
deep-ultraviolet (deep-UV) nonlinear optical (NLO)
material K3Ba3Li2Al4B6O20F is developed mainly by the element substitution
of Be for Al and Li from Sr2Be2B2O7 that was considered as one of the most promising deep-UV
NLO materials. K3Ba3Li2Al4B6O20F preserves the structural merits of Sr2Be2B2O7 and thus exhibits
no layering growth tendency and possesses the optical properties required
for deep-UV NLO applications, including deep-UV transparency, phase-matchability,
and sufficiently large second-harmonic generation (1.5 × KH2PO4). Furthermore, it overcomes the structural
instability problem of Sr2Be2B2O7, which is confirmed by the obtainment of large single crystals
and phonon dispersion calculations. These attributes make it very
attractive for next-generation deep-UV NLO materials. The substitution
of Be for Al and Li in beryllium borates provides a new opportunity
to design beryllium-free deep-UV NLO materials with good performance.