Nonlinear optical response and characteristic Raman spectra of phagraphene quantum dots

In the field of optoelectronics, quantum dots (QDs) have gained interest due to the easy modification of electronic properties. Subsequently, the importance of nonlinear optical (NLO) properties is increasing day by day. In this work, we have systematically analyzed the NLO properties of phagraphene QDs with different shapes and sizes, employing density functional theory (DFT). A negative value of cohesive energy and the absence of imaginary modes in the Raman spectra confirm the energetical stability of the QDs. Successful experimental realization of phagraphene nanoribbon has triggered the possibility of experimental feasibility of the QDs. Additionally, most of the QDs showcase high absorption in the UV region. Particularly, the variation of electronic bandgap and the number of delocalized pi electrons in the structure control the NLO responses of materials. Both the electronic bandgap and the number of pi electrons in the system can be tuned easily by varying the shapes and sizes of the phagraphene QDs. Both static and dynamical variations of polarizability alpha, first-order beta, and second-order hyperpolarizability gamma are calculated here. Maximum value of alpha, beta and gamma are observed for different QDs. The variation of NLO responses with perturbing electric fields leads to the feasibility of applications in optoelectronics.