Three-step seedless synthesis of ultralong gold nanorods

Ultralong gold nanorods with an average aspect ratio up to 77 and average length up to 1.6 mu m were obtained by using the three-step seedless wet chemistry growth method. The prepared ultralong gold nanorods were pentatwinned. The effects of the amount transferred from flask B to C, and the pH value in the growth solution C on the synthesized ultralong gold nanorods were investigated by using the scanning electron microscopy images. Results showed that ultralong gold nanorods with tunable average aspect ratio from 24 to 77 were obtained by changing the amount transferred from flask B to C and the pH value in the growth solution C. Due to the large aspect ratio of the prepared gold nanorods, the longitudinal surface plasmon resonance wavelength of the ultralong gold nanorods was expected in the infrared wavelength region. Moreover, 2 mu m mid-infrared pulsed laser output was achieved in a passively Q-switched solid-state laser by using the prepared ultralong gold nanorods as the saturable absorber. Our method offers a new facile strategy to obtain ultralong gold nanorods with tunable aspect ratios, which have wide applications in areas such as photonics and optoelectronics.