Browsing by Author "Yeh, Te-Fu"

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Roles of nitrogen functionalities in enhancing the excitation-independent green-color photoluminescence of graphene oxide dots
(2017-06-28)
Teng, Chiao-Yi
;
Ba-Son Nguyen
;
Yeh, Te-Fu
;
Lee, Yuh-Lang
;
Chen, Shean-Jen
Fluorescent graphene oxide dots (GODs) are environmentally friendly and biocompatible materials for photoluminescence (PL) applications. In this study, we employed annealing and hydrothermal ammonia treatments at 500 and 140 degrees C, respectively, to introduce nitrogen functionalities into GODs for enhancing their green-color PL emissions. The hydrothermal treatment preferentially produces pyridinic and amino groups, whereas the annealing treatment produces pyrrolic and amide groups. The hydrothermally treated GODs (A-GODs) present a high conjugation of the nonbonding electrons of nitrogen in pyridinic and amino groups with the aromatic pi orbital. This conjugation introduces a nitrogen nonbonding (n(N 2p)) state 0.3 eV above the oxygen nonbonding state (n(O 2p) state; the valence band maximum of the GODs). The GODs exhibit excitation-independent green-PL emissions at 530 nm with a maximum quantum yield (QY) of 12% at 470 nm excitation, whereas the A-GODs exhibit a maximum QY of 63%. The transformation of the solvent relaxation-governed pi* -> n(O 2p) transition in the GODs to the direct pi* -> n(N 2p) transition in the A-GODs possibly accounts for the substantial QY enhancement in the PL emissions. This study elucidates the role of nitrogen functionalities in the PL emissions of graphitic materials and proposes a strategy for designing the electronic structure to promote the PL performance.
Three-dimensional patterned graphene oxide-quantum dot microstructures via two-photon crosslinking
(2017-12-01)
Lin, Chun-Yu
;
Chang, Hsin-Yu
;
Yeh, Te-Fu
;
Teng, Hsisheng
;
Chen, Shean-Jen
The two-photon crosslinking of graphene oxide-quantum dots (GOQDs) adopts rose Bengal as the photoactivator to induce the GOQD assembly process. Based on the Forster resonance energy transfer mechanism with oxygen as the crosslinking medium, three-dimensional patterned GOQD microstructures with near diffraction-limit spatial resolution have been fabricated and analyzed by a multiphoton excited fabrication instrument/microscope. (C) 2017 Optical Society of America