Tailoring nonlinear optical crystal borophosphate through the introduction of transition metal d orbitals for improving optical anisotropy and SHG response: a first-principles investigation

Abstract

Motivated by the discovery of practical and economical nonlinear optical (NLO) materials with strong second harmonic generation (SHG), experimental and theoretical researches have been widely carried out. However, drawbacks in one or some respects, especially poor birefringence, preclude their use for NLO applications in optoelectronic technologies. In the present work, taking the case of nonlinear material borophosphate BPO4, a systematic calculation of the structure, electronic, linear and nonlinear optical properties of the BP1−xVxO4 systems (x = 0, 0.25, 0.5, 0.75, and 1) are presented to tailor its small birefringence and assess their ultraviolet NLO capabilities based on first-principles calculations. Particularly, birefringences of the four V-containing compounds are significantly enhanced to fulfill the phase matching conditions in the ultraviolet region. Meanwhile, their SHG responses are greatly improved, especially for BP0.5V0.5O4, with moderate optical anisotropy of refraction (about 0.08 in transparent regions) and strong second harmonic generation response (almost ten times as compared with BPO4). Besides, a detailed analysis of their electronic characters, the polarizability anisotropy and local dipole moments of asymmetry functional building [BO4]5−, [PO4]3−, and [VO4]3− units are elucidated to understand the high performance of BP1−xVxO4 systems. These candidates would extend the ultraviolet nonlinear optical materials. Furthermore, the strategy of introducing transition metal d orbitals could be a promising way to tailor electronic structures and optical anisotropy in other functional materials for advanced photonic devices.