Evidence of “new hot spots” from determining the nonlinear optical behavior of materials: mechanistic studies of the vanadium borate crystal, Na₃VO₂B₆O₁₁

Abstract

A novel mechanism for the nonlinear optical (NLO) effects of vanadium borate crystals, Na3VO2B6O11 (NVB), with distorted VO4 groups was investigated. A comprehensive analysis of the structure-property relationship was performed by combining the experimental measurements, the electronic structures calculations, the SHG-weighted electron density and the real-space atom-contribution analysis to yield the linear and nonlinear optical properties. The contribution of a (VO4)(3-) anionic group to the second harmonic generation (SHG) response was more pronounced than that of the (BO3)(3-) anionic group, which plays a virtual role in the SHG effects in NVB. The anionic (BO3)(3-) groups make dominant contributions to the birefringence, whereas the contribution of the V(5+) cations to these linear optical effects is negligible.

Structural Insights into Borates with an Anion‐Templated Open‐Framework Configuration: Asymmetric K2BaB16O26 versus Centrosymmetric K3CsB20O32 and Na2M2NB18O30 (M=Rb, Cs; N=Ba, Pb)

“…An exhaustive enumeration of all the possible multi‐ternary cation combinations is impossible, and hence intuitive guidance is imperative for future success. For nonlinear optical (NLO) borate materials, it has been consistently shown that the presence of metal‐centered groups (e.g., Pb−O and V−O groups), which induce the hybridization states with O‐2p, is beneficial for the states close to the band gap dominating the optical properties of a crystal, whereas delocalized conduction bands of n s 1 cations (Na + , Rb + , Cs + ) are desirable for large band gaps and have success in producing NLO‐active materials with shorter optical absorption at around 220 nm. Fortunately, the direct combination of n s 1 (Na + , Rb + , Cs + ) and n s 2 (Ba 2+ ) cations generally maintains the large band gaps of the borates.…”

Na6MQ4 (M=Zn, Cd; Q=S, Se): Promising New Ternary Infrared Nonlinear Optical Materials

“…To further confirm that the asymmetric NaQ 4 units could be used as NLO‐active units, we carried out statistical analyses on the origins of the SHG effect in the Na‐containing chalcogen compounds in the Inorganic Crystal Structure Database (ICSD), as shown in Tables S6–7 and Figures S9–10 in the Supporting Information. Based on the analyses of Mulliken overlap population in the NaS 4 units (Figure S10 in the Supporting Information), we can see that the shorter bond length can produce stronger overlap of the charge density in ionic Na−S bonding [60, 61] . Meanwhile, the NaS 4 units show a significant contribution to the SHG response if the value of Na−S Mulliken overlap population in the NaS 4 units exceeds about 0.2.…”

NaBa4(GaB4O9)2X3 (X = Cl, Br) with NLO-Active GaO4 Tetrahedral Unit: Experimental and ab Initio Studies

“…Using the length-gauge formalism at a zero frequency limit, the SHG coefficients can be estimated, which can be described as a later developed transform by Zhang et al: Here, the total SHG coefficient χ αβγ (2) is divided into the contribution from two different processes which are virtual-electron (VE) and virtual-hole (VH) . The theoretical methods have been applied with success to analyze the SHG coefficients of NLO crystal materials in previous study. , …”