Probing the linear and nonlinear optical properties of nitrogen-substituted carbon nanotube

In view of their intriguing structural and electrical properties, the linear and nonlinear optical (NLO) responses of six carbon nanotube (CNT) molecules substituted by nitrogen atoms at one end have been explored by using the CAM-B3LYP method. Molecules 1, 2 and 3 were obtained by increasing the lengths of the CNTs, and 1-Li, 2-Li and 3-Li were constructed by doping one Li atom into the N-substituted end of 1, 2 and 3 (mentioned above), respectively. Two effective approaches have been proposed to increase nonlinear optical properties(NLO): increasing the length of the CNT as well as doping one Li atom into the N-substituted end. The results show that both the linear polarizabilities (alpha (0)) and nonlinear first hyperpolarizabilities (beta (tot)) values increase with increasing the lengths of the CNTs: 188 of 1 < 307 of 2 < 453 of 3 for alpha (0) and 477 of 1 < 2654 of 2 < 3906 au of 3 for beta (tot). Significantly, compared with the non-doped CNTs, the beta (tot) values are remarkably enhanced by doping one Li atom into the N-substituted end: 477 of 1 < 23258 of 1-Li, 2654 of 2 < 37244 of 2-Li, and 3906 of 3 < 72004 au of 3-Li. Moreover, the beta (vec) values show a similar trend to the beta (tot) values. Our results may be beneficial to experimentalists in exploring high-performance nonlinear optical materials based on CNT.