Tuning the Emission Energy of Chemically Doped Graphene Quantum Dots.
Tuning the emission energy of graphene quantum dots (GQDs) and understanding the reason of tunability is essential for the GOD function in optoelectronic devices. Besides material-based challenges, the way to realize chemical doping and band gap tuning also pose a serious challenge. In this study, we tuned the emission energy of GQDs by substitutional doping using chlorine, nitrogen, boron, sodium, and potassium dopants in solution form. Photoluminescence data obtained from (Cl- and N-doped) GQDs and (B-, Na-, and K-doped) GQDs, respectively exhibited red- and blue-shift with respect to the photoluminescence of the undoped GQDs. X-ray photoemission spectroscopy (XPS) revealed that oxygen functional groups were attached to GQDs. We qualitatively correlate red-shift of the photoluminescence with the oxygen functional groups using literature references which demonstrates that more oxygen containing groups leads to the formation of more defect states and is the reason of observed red-shift of luminescence in GQDs. Further on, time resolved photoluminescence measurements of Cl- and N-GQDs demonstrated that Cl substitution in GQDs has effective role in radiative transition whereas in N-GQDs leads to photoluminescence (PL) quenching with non-radiative transition to ground state. Presumably oxidation or reduction processes cause a change of effective size and the bandgap.
Department of Physics, The Islamia University of Bahawalpur, 63100 Bahawalpur, Pakistan. noorulain3@yahoo.com.
Noor-Ul-Ain
Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden. marer@ifm.liu.se.
Martin O
MO
Eriksson
Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden. sussc@ifm.liu.se.
Susann
S
Schmidt
Department of Physics, The Islamia University of Bahawalpur, 63100 Bahawalpur, Pakistan. mhashmi@iub.edu.pk.
M
M
Asghar
Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden. pinli332@student.liu.se.
Pin-Cheng
PC
Lin
Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden. poh@ifm.liu.se.
Per Olof
PO
Holtz
Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden. misyv@ifm.liu.se.
Mikael
M
Syväjärvi
Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden. yazdi@ifm.liu.se.
G Reza
GR
Yazdi
XPS; emission energy; graphene quantum dots; photoluminescence; time resolved photoluminescence