Tetragonal Silicene and Germanene Quantum Dots: Candidates for Enhanced Nonlinear Optical and Photocatalytic Activity

Over the past decade, quantum dots (QDs), based on two-dimensional (2D) materials have gained interest due to their numerous applications in the field of photonics. In this study, tetragonal silicene (T-Si) and tetragonal germanene (T-Ge) QDs with different shapes and sizes are systematically analyzed within the ab initio framework. All of these energetically favorable QDs are well suited for experimental design. In particular, these QD structures exhibit a range of electronic energy gaps depending upon specific morphology, which leads to enhanced nonlinear optical (NLO) characteristics in a broad spectrum. Moreover, the signature Raman modes of T-Si and T-Ge sheets have been critically explored by performing vibrational analysis of these QDs. These QDs also show optical absorption in the visible range and better light-harvesting efficiency, owing to which they can be helpful in designing solar cells. Outstanding second- and third-order NLO responses, such as second harmonic generation, optical Pockels effect, and Kerr effect in the presence of a perturbing external field, make these QD materials potentially efficient in the nonlinear optical field and photonics application. Furthermore, these QDs can participate in metal-free water splitting photocatalysis toward a pollutant-free green environment.