Size-dependent luminescence and two-photon excitation cross sections in graphene oxide quantum dots
黃柏庭1*, 劉淑白1, 鄧喬乙2, 鄧熙聖1,2, 陳顯禎1, 林光儀**1
1Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan, Taiwan
2Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan
* presenting author:Bo-Ting Huang, email:aherican@gmail.com
Fluorescent carbon materials have attracted considerable attention due to their low toxicity, excellent biocompatibility, low cost, high resistance to photobleaching, and an abundance of raw materials in nature [1]. Tailoring the size of graphene oxide quantum dots (GOQDs) and understanding the band gap tuning mechanism are essential for the applications of GOQDs in opto-electronics. [2,3]. In this study, GOQDs are prepared using a modification of Hummers’ method with natural graphite powder. Photoluminescence (PL) spectra have been studied in GOQDs by varying their size. GOQDs exhibit strong quantum-confinement effects. This PL can be ascribed to the irradiative excitation of electrons from the non-bonding oxygen (n) states to the graphene anti-bonding p orbital with subsequent relaxation of the electrons to the n ground states [4]. Nitrogen-doping reduces vacancy defects and donates electrons to compensate for the unbalanced charge in p-type GOQDs, thereby increasing the PL quantum yield. In addition, we report quantitative measurements of two-photon excitation action cross sections of GOQDs at excitation wavelengths of 800 nm. Two-photon excitation cross-sections provide a reliable database for two-photon fluorescence microscopy [5]. We use a Ti:sapphire laser as excitation source with 120 fs pulse width, and excitation wavelengths are 800 nm for two-photon luminescence. The GOQDs can emit quite strong two-photon induced luminescence. Therefore, the GOQDs show considerable promise for phosphors used in light-emitting devices and probes employed in two-photon excitation microscopy.
[1] J. Peng et al., Nano Lett. 12, 844 (2012).
[2] S. H. Jin et al., ACS Nano 7, 1239 (2013).
[3] S. Kim et al., Appl. Phys. Lett. 101, 163103 (2012).
[4] C. Y. Teng et al., J. Mater. Chem. C 3, 4553 (2015).
[5] L. C. Cheng et al., Biomed. Opt. Express 5, 3427 (2014).
Funding: MOST103-2112-M-006-002
**E-mail: kilin@mail.ncku.edu.tw


Keywords: graphene oxide quantum dots , size-dependent, two-photon excitation, luminescence, cross section