Two-Photon-Excited Emission of Quantum Dots with a Plasmonic Chip

Abstract

Plasmonic chips have wavelength-size periodic structures coated with thin metal films and can provide enhanced electric fields near the chip surfaces. Herein, a plasmonic chip was developed to carry out one-photon-excited emission (1PE) and two-photon-excited emission (2PE). Most studies on plasmonassisted 2PE are based on the localized surface plasmon resonance. Among the propagated surface plasmon resonances (SPRs), we focused on the grating-coupled SPR. Quantum dots (QD655) dispersed on the silver plasmonic chip of the bull's eye patterns with a 600 nm pitch were excited by a near-infrared (NIR) laser with λ = 1064 nm. The emission intensity plotted against the irradiation light intensity was well fitted to a quadratic function for the plasmonic chip and coverslip. Therefore, the emission excited by NIR light was evaluated as 2PE. The coefficient of the quadratic part for the plasmonic chip was larger than that for the coverslip, and our plasmonic chip was found to promote the two-photon excitation. After correcting the molecule number at illumination spots, the enhancement factor of the 2PE evaluated in the plasmonic chip was found to be greater than 6-fold compared with that in the coverslip. The enhanced 2PE was assisted by the propagated plasmon field in the bull's eye-patterned plasmonic chip.