Journal
ACS NANO
Volume 7, Issue 2, Pages 1239-1245Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nn304675g
Keywords
graphene quantum dots; photoluminescence; functionalization; density functional theory; band gap
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Funding
- Converging Research Center Program through the National Research Foundation of Korea (NRF)
- Ministry of Education, Science, and Technology [2011K000623]
- Center for Advanced Soft Electronics under the Global Frontier Research Program of the Ministry of Education, Science and Technology [2011-0031630]
- GRC project of KAIST Institute for the NanoCentury
- National Research Council of Science & Technology (NST), Republic of Korea [JX130004] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
- National Research Foundation of Korea [2011-0031630] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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The band gap properties of graphene quantum dots (GQDs) arise from quantum confinement effects and differ from those in semimetallic graphene sheets. Tailoring the size of the band gap and understanding the band gap tuning mechanism are essential for the applications of GQDs in opto-electronics. In this study, we observe that the photoluminescence (PL) of the GQDs shifts due to charge transfers between functional groups and GQDs. GQDs that are functionalized with amine groups and are 1-3 layers thick and less than 5 nm in diameter were successfully fabricated using a two-step cutting process from graphene oxides (GOs). The functionalized GQDs exhibit a redshift of PL emission (ca. 30 nm) compared to the unfunctionalized GQDs. Furthermore, the PL emissions of the GQDs and the aminefunctionalized GQDs were also shifted by changes in the pH due to the protonation or deprotonation of the functional groups. The PL shifts resulted from charge transfers between the functional groups and GQDs, which can tune the band gap of the GQDs. Calculations from density functional theory (DFT) are in good agreement with our proposed mechanism for band gap tuning in the GQDs through the use of functionalization.
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