Tuning the Emission Energy of Chemically Doped Graphene Quantum Dots

Abstract

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.

Synthesis, Purification, and Characterization of Carbon Dots from Non-Activated and Activated Pyrolytic Carbon Black

“…The PL shift was even higher in the carbon dots from activated precursors (Cd.CB < Cd.H 2 SO 4 < Cd.H 2 SO 4 + KOH < Cd.KOH). A hypsochromic or bathochromic shift is caused by a bandgap modification [ 73 , 74 , 75 , 76 ]. A hypsochromic PL shift is observed with a widening of the bandgap, while the opposite (a bathochromic shift) occurs by narrowing the bandgap [ 73 ].…”

“…A hypsochromic or bathochromic shift is caused by a bandgap modification [ 73 , 74 , 75 , 76 ]. A hypsochromic PL shift is observed with a widening of the bandgap, while the opposite (a bathochromic shift) occurs by narrowing the bandgap [ 73 ]. This bandgap is highly dependent on the nanoparticle size and the surface functionalization.…”

Thermal Effect of Sulfur Doping for Luminescent Graphene Quantum Dots

“…Several synthesis methods were reported recently. [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] Minati et al [22][23] investigated the photoluminescence spectra of short oxidized multi walled carbon nanotubes which are luminescent in the visible range. Minati et al 24 and his group in 2010 reported a new method for the high yield isolation of strongly photoluminescent GQD from oxidized carbon nanotubes (ox-CNT).…”

“…Qu et al 20 have demonstrated that S, N-GQDs processed much better absorption of visible light than pure GQDs and multicolor emission under visible light excitation. Ain et al 29 observed the red and blueshift, obtained from PL, by substitutional doping while using different dopants [Cl, N, Na, K, B] to tune the emission energy of GQDs. Zhou et al 30 prepared a simple and efficient method of the photo-Fenton reaction after breaking C-C bond of GO to produce GQDs in large scale.…”

Tailoring Blue-Green Double Emissions in Carbon Quantum Dots via Co-Doping Engineering by Competition Mechanism between Chlorine-Related States and Conjugated π-Domains

“…Once the reagent of BD continues to increase, the enlarged particle size of CQDs reduced the distance between CQDs (as shown in Figure 2 ), so that the π–π interaction can be effectively occurred, which finally resulted in hypochromic effect [ 82 , 83 ]. Moreover, Noor-Ul-Ain reported doping chlorine into CQDs would introduce additional energy level between the C π -C π *, called the Cl-related states [ 84 ]. The corresponding absorption peak at 292 nm observed in our samples coincided with the calculated transition energy from C π to Cl-related states [ 28 , 69 ].…”