K, Rb-hydroxyborates series with deep-ultraviolet KRbB5O8(OH) possessing moderate second harmonic generation response

Abstract

Herein, we reported three new hydroxyborate crystals, KRbB₅O₈(OH) (I), KRbB₆O₉(OH)₂ (II), and K_3.3Rb_0.7B₁₀O₁₅(OH)₄ (III), synthesized via a high-temperature solution method and hydrothermal method. Among them, I features a short deep-UV cut-off edge (190 nm), a moderate phase-matching second harmonic generation (SHG) response (0.9 × KDP), and an experimental birefringence of 0.025@546.1 nm. Besides, the syntheses, crystal structures, refractive indexes, and thermal properties of I, II, and III were investigated. In addition, the first-principles calculation was conducted to comprehend the relationship between the microstructure and macro optical property of I.