The effect of co-substitution of heterovalent ions Ga3+ and Sb5+ on nonlinear optical properties of phosphate crystals

Abstract

The strong second harmonic response of nonlinear optical (NLO) materials is of great scientific significance for laser technology. The second harmonic generation (SHG) response in NLO crystals is usually enhanced by introducing non-centrosymmetric active structural units with permanent hyperpolarizability into the structure. We have designed and grown a series of Ga³⁺:Sb⁵⁺:KTiOPO₄ crystals based on traditional KTiOPO₄ by co-doping Ga and Sb ions. The chemical compositions of the crystals were determined through inductively coupled plasma atomic emission spectroscopy (ICP-AES). The electronic structure was analyzed by X-ray photoelectron spectroscopy (XPS), and it was determined that the chemical strengths of Ti–O K–O and P–O bonds are related to the binding energy difference. After the introduction of doping ions, the frequency doubling conversion efficiency increased from 1064 to 532 nm, up to approximately 22%. And the SHG responses of Ga³⁺:Sb⁵⁺:KTP crystals have significantly enhanced, with a NLO coefficient close to 1.25 times that of KTP crystals. First-principles calculations and structural analyses show that the improved SHG response of Ga³⁺:Sb⁵⁺:KTP crystals is mainly influenced by the [SbO₆] groups. This study provides a new illustration for improving the NLO performance of crystals.