Charge-transfer induced large nonlinear optical properties of small Al Clusters: Al4M4

TL;DR

This study reveals that small Al4M4 clusters with alkali atoms exhibit exceptionally high linear and nonlinear optical responses due to charge transfer and non-centrosymmetry, making them promising for advanced NLO devices.

Contribution

It demonstrates that Al4M4 clusters have unprecedented NLO properties driven by charge transfer and aromaticity, surpassing conventional systems of similar size.

Findings

Al4M4 clusters show extremely high NLO coefficients.

Charge transfer and non-centrosymmetry enhance optical properties.

Clusters exhibit potential for next-generation NLO applications.

Abstract

We investigate the linear and nonlinear electric polarizabilities of small Al4M4 (M=Li, Na and K) clusters. Quantum chemical calculations reveal that these compounds exhibit an exceptionally high magnitude of linear and nonlinear optical (NLO) coefficients which are orders of magnitude higher than the conventional pi-conjugated systems of similar sizes. We attribute such phenomenal increase to non-centrosymmetricity incorporated in the systems by the alkali atoms surrounding the ring leading to charge transfer with small optical gap and low bond length alternation (BLA). Such a low magnitude of the BLA from a different origin, suggests the possibility that these clusters are aromatic in character and along with the large NLO coefficients they appear to be better candidates for next generation NLO fabrication devices.