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Electronic Supplementary Information
Roles of Nitrogen Functionalities in Enhancing the
Excitation-Independent Green-Color Photoluminescence of
Graphene Oxide Dots
Chiao-Yi Teng,a Ba-Son Nguyen,a Te-Fu Yeh,a Yuh-Lang Lee,a Shean-Jen Chen,b and
Hsisheng Teng*a
aDepartment of Chemical Engineering and Research Center for Energy Technology and
Strategy, National Cheng Kung University, Tainan 70101, Taiwan
bCollege of Photonics, National Chiao Tung University, Tainan 71150, Taiwan
*To whom correspondenec should be addressed. E-mail: [email protected], Tel:
886-6-2385371, Fax:886-6-2344496
Supporting Information for:
(1) Color and quantum yield of graphene oxide dots
(2) Color and quantum yield of carbon dots
(3) TEM images of GODs
(4) XPS analysis of NGODs and GODs
(5) Raman spectra of the GO-based dots
(6) FTIR spectra of the GO-based dots
(7) PL quantum yield measurements
(8) The Mott-Schottky equation for the conductivity-type determination
Electronic Supplementary Material (ESI) for Nanoscale.This journal is © The Royal Society of Chemistry 2017
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(9) UPS analysis for valence band maxima of the GO-based dots
(10) Application of A-GODs as a phosphor for white-light emission
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1. Color and quantum yield of graphene oxide dots Table S1 Summary of the color/wavelength (λ) and quantum yield (QY) of photoluminescence emissions from graphene oxide dots synthesized through top-down and bottom-up routes.
color/λ (nm) QY (%) heteroatom
(source) precursor
(synthesis) Ref.
top-down
ultraviolet/360 28 nitrogen
(poly(ethylene glycol)) GO
(hydrothermal) 1
violet/407* 3.4 − GO
(ultrasonic) 2
violet/413 35 nitrogen
(ammonia) GO
(hydrothermal) 3
violet/423 7.1 − graphite flask, CNT (electrochemical) 4
violet/425 8.6 nitrogen
(ammonia) GO
(hydrothermal) 5
violet/430 46 nitrogen
(ammonia) GO
(hydrothermal) 6
violet/430 6.9 − GO
(hydrothermal) 7
violet/430 12 nitrogen
(dimethylformamide) GO
(solvothermal) 8
blue/450 23 − GO
(microwave) 9
blue/450 7.4 nitrogen
(poly(ethylene glycol) diamine) GO
(chemical-oxidation) 10
blue/450 9.7 nitrogen
(dimethylformamide) graphite nano-particles
(solvothermal) 11
blue/460 21 nitrogen
(poly(ethylenimine)) GO
(hydrothermal) 12
cyan/490* 13 boron
(borax) graphite rod
(electrochemical) 13
cyan/500 74 nitrogen
(dimethylformamide) GO
(solvothermal) 14
cyan/500 12 − GO
(microwave) 9
green/515 11 nitrogen
(dimethylformamide) GO
(solvothermal) 15
green/516 12 nitrogen
(dimethylformamide) GO
(solvothermal) 16
green/520 31 nitrogen
(dimethylformamide) GO
(solvothermal) 17
green/520 14 nitrogen (insulin)
carbon black (acidic-refluxing) 18
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green/520 18 nitrogen
(dimethylformamide) graphite nano-particles
(solvothermal) 11
green/540* 14 − graphite rod
(electrochemical) 19
yellow/570 6.9 nitrogen
(dimethylformamide) graphite nano-particles
(solvothermal) 11
yellow/570 2.3 − carbon black
(acidic-refluxing) 20
red/640 15 nitrogen
(dimethylformamide) graphite nano-particles
(solvothermal) 11
bottom-up
violet/402* 84 nitrogen
(melamine) melamine (pyrolysis) 21
violet/425* 40 nitrogen
(ammonia) citric acid
(hydrothermal) 22
violet/435* 78 nitrogen/sulfur (urea/thiourea)
citric acid (hydrothermal) 23
violet/436* 79 nitrogen
(melamine) melamine (pyrolysis) 21
blue/440 54 − L-glutamic acid
(pyrolysis) 24
blue/450* 94 nitrogen
(ethylene diamine) citric acid
(hydrothermal) 25
blue/452 37 nitrogen
(dicyandiamide) citric acid
(hydrothermal) 26
blue/470 21 nitrogen
(hydrazine) pyrene
(hydrothermal) 27
blue/473 11 − glucose
(microwave) 28
blue/474 12 − glucose
(microwave) 29
cyan/490 45 nitrogen
(hydrazine) pyrene
(hydrothermal) 27
cyan/495* 76 nitrogen
(melamine) melamine (pyrolysis) 21
cyan/510 3.8 − hexabenzocoronene
(pyrolysis) 30
green/524* 44 nitrogen/chlorine
(ethylenediamine/HCl) glucose
(hydrothermal) 31
green/530 23 nitrogen
(hydrazine) pyrene
(hydrothermal) 27
green/535* 12 sulfur
(Na2S) pyrene
(hydrothermal) 32
green/560* 71 nitrogen
(precursor) o-phenylenediamine
(electrochemical) 33
yellow/570 70 nitrogen
(hydrazine) pyrene
(hydrothermal) 27
yellow/570 75 nitrogen
(ammonia) glucose
(basic-mixing) 34
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orange/587* 72 nitrogen
(precursor ) melamine (pyrolysis) 21
*excitation independent
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2. Color and quantum yield of carbon dots
Table S2 Summary of the color/wavelength (λ) and quantum yield (QY) of
photoluminescence emissions from carbon dots synthesized from the bottom-up route.
color/λ (nm) QY (%) heteroatom (source) precursor
(synthesis) Ref.
bottom-up
violet/390 42 nitrogen
(melamine) citric acid
(hydrothermal) 35
violet/415 73 nitrogen/sulfur
(L-cysteine) citric acid
(hydrothermal) 36
violet/420 99 nitrogen
(2-aminoethanol) citric acid
(microwave) 37
violet/430 30 nitrogen/phosphorous
(ammonia/phosphoric acid) glucose
(hydrothermal) 38
blue/450 83 nitrogen/magnesium
(ethylenediamine/Mg(OH)2) citric acid
(hydrothermal) 39
blue/450 28 nitrogen
(ethylenediamine) poly(saccharide) (hydrothermal) 40
blue/450* 80 nitrogen/boron
(ethylenediamine/boric acid) citric acid
(hydrothermal) 41
blue/450* 85 nitrogen
(ethylenediamine) citric acid
(hydrothermal) 42
yellow/568* 33 nitrogen
(precursor) triaminobenzene
(solvotherml) 43
yellow/573* 38 nitrogen
(precursor) o-phenylenediamine
(microwave) 44
red/620* 47 nitrogen/sulfur/copper (L-cysteine/CuCl) HEDTAa
(microwave) 45
*Excitation independent
aN-(hydroxyethyl)-ethylenediaminetriacetic acid
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3. TEM images of GODs
Fig. S1 Morphology and crystal structure of GODs. (a) TEM image with the inset showing
the histogram of size distribution. (b) HRTEM image of a GOD particle, showing graphene
{1100 } lattice planes with a d-spacing of 0.213 nm.
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4. XPS analysis of NGODs and GODs
Fig. S2 XPS spectra of NGODs and GODs. (a) Full-range spectrum of NGODs. (b)
Full-range spectrum of GODs. (c) C 1s spectrum of NGODs. (d) C 1s spectrum of GODs. (e)
N 1s spectrum of NGODs. C 1s and N 1s spectra are decomposed into several peaks
(indicated by dashed lines) and fitted using a Gaussian function.
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5. Raman spectra of the GO-based dots
Fig. S3 Raman spectra of GODs, NGODs, A-GODs, and A-NGODs. The dash lines
indicate the positions of the D, G, D’, and 2D bands of GODs.
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6. FTIR spectra of the GO-based dots
Fig. S4 FTIR spectra of GODs, NGODs, A-GODs, and A-NGODs.
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7. PL quantum yield measurements
A highly reliable method for evaluating the PL quantum yield (QY) is the
comparative method of Williams et al.,48 which involves the use of well characterized
standard samples with known QY values. Plot a graph of integrated fluorescence intensity
from fluorescence spectrum vs. absorbance from UV-vis absorbance spectrum. Repeat above
steps for five solutions with increasing concentrations of the standards and samples. The PL
QY of the samples were calculated in accordance with the following cross-calibration
equation,49
st2st
2x
st
xx YQ
ηη
GradGradYQ
= (3)
where Grad is the gradient of the plot of fluorescence intensity vs. absorbance and η is the
reflective index of the solvent. Note that “x” refers to the sample and subscript “st” refers to a
standard with known quantum yield (the values of QYst here for a fluorescein-ethanol solution
and a rhodamine 6G-ethanol solution are 0.79 and 0.95, respectively50,51). In order to
minimize re-absorption, absorbance in the 10×10 mm fluorescence cuvette was kept below
0.1 at an excitation wavelength 470 nm. For each test sample, two QYx values were obtained,
one relative to standard A, the other to standard B. The QY of the sample was then taken as
the average of the two values. Fig. S5 presents the typical fluorescence and absorbance
measurements for an A-GOD dispersion and a fluorescein-ethanol standard solution. Fig. S6
shows the determination of the gradients in the plots of fluorescence intensity vs. absorbance
for the two standards and the A-GODs. Table S3 presents the gradients and PL QY of the
GO-based dots determined using the data of Figs. S5 and S6 in compliance with Eq. (3).
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Fig. S5 PL spectra of (a) the A-GODs dispersion (0.1 mg mL-1) and (b) the
fluorescein-ethanol standard solution (0.03 mg mL-1). Absorption spectra of (c) the A-GODs
dispersion and (d) the fluorescein-ethanol standard solution.
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Fig. S6 Plots of PL intensity vs. absorbance for Rhodamine 6G (black line), fluorescene
(red line), and A-GODs (blue line). Note that the gradient of the lines is proportional to the
QY of the corresponding sample.
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Table S3 The gradients and PL QY of the GO-based dots determined using the data of
Figs. S5 and S6 in compliance with Eq. (3).
Gradx QYFL QYR6G QYaverage GODs 526276.4 0.11 0.12 0.12 NGODs 669806.3 0.14 0.15 0.14 A-GODs 2918441.7 0.61 0.65 0.63 A-NGODs 2679225.1 0.56 0.60 0.58
The parameters used in Eq (3):
GradFL = 3614712.3
GradR6G = 4085559.7
ηwater = 1.33
ηethanol = 1.36
QYFL = 0.79
QYR6G = 0.95
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8. The Mott-Schottky equation for the conductivity-type determination
The GODs were deposited on a glassy carbon substrate. The conductivity types and Fermi
level (EF) potentials of the GOD films were then determined via electrochemical impedance
spectroscopic analysis based on the Mott-Schottky equation,46,47 i.e.
)(21F
02 e
kTEENeC D
−−=εε
for n-type conductivity
)(21F
02 e
kTEENeC A
++−−=εε
for p-type conductivity
where C represents the capacitance of the space−charge region, ε0 is the vacuum permittivity,
ε is dielectric constant of semiconductors, e is the electron charge, E is applied potential, EF is
the Fermi level potential, k is the Boltzmann constant, T is the absolute temperature, and NA
(ND) is the acceptor (donor) density. Nota that the temperature term is generally small and can
be neglected. The capacitance values of the space−charge region were obtained at various
applied potentials. According to the Mott-Schottky equation, 1/C2 and E are linearly related,
with a negative slope indicating p-type conductivity and a positive slope indicating n-type
conductivity.
Fig. S7 presents the variation of the capacitance in the space-charge region of the GODs
and A-GODs with the applied potential in compliance with the Mott–Schottky equation.
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Fig. S7 Variation of capacitance (C) with applied potential in 2 M H2SO4 presented in the
Mott-Shottky relationship for electrodes deposited with (a) GODs and (b) A-GODs. The
capacitance was determined by electrochemical impedance spectroscopy and the negative and
positive slopes correspond to p- and n-type conductivities, respectively.
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9. UPS analysis for valence band maxima of the GO-based dots
To identify the valence band maxima (i.e., the n-state, denoted as Ev), the GODs were
deposited on the silicon substrate and the value of Ev was determined using UPS with He I
light (21.2 eV) irradiation. The UPS analysis was performed in accordance with:
EB + Ek + ϕ = 21.2 (1)
where EB is the binding energy measured from the Fermi level, Ek is the kinetic energy of
electrons, ϕ is the work function of the GODs, and 21.2 eV is the excitation energy of the He
I light.
Ev was then calculated as:
Ev = 21.2 − (EB2 − EB1) (2)
where EB2 is the secondary cutoff binding energy in the UPS spectra, in which the Ek of the
excited electrons is equal to 0 and the EB1 is the difference between the Fermi edges and the
valence band edges. Fig. S8 shows the UPS spectra of the GODs and A-GODs. Note that EB1
can be determined from the intercepts of the extrapolated straight lines on the abscissa at low
binding energy. Similarly, EB2 can be estimated using the secondary cutoff values (Ek = 0 eV)
in the UPS spectra, which are obtained from the intercepts of the extrapolated straight lines
on the abscissa at high binding energy. The UPS widths is obtained directly as the difference
between EB2 and EB1. Finally, Ev is obtained by subtracting these UPS widths from the
excitation energy (21.2 eV).
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Fig. S8 UPS spectra of the samples: (a) GODs and (b) A-GODs. The VBM levels with
respect to the Fermi levels were determined from the intercepts of the extrapolated straight
lines (blue dashed line) on the abscissa at low binding energy. The intersections of the tangent
(red dashed line) with the abscissa at high binding energy give the secondary electron onset
binding energy. The UPS widths (black lines) can be determined by these two intercept
binding energies, and the VBM levels can be calculated by subtracting these widths from the
excitation energy (21.2 eV).
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10. Application of A-GODs as a phosphor for white-light emission
We mixed aqueous solutions of A-GOD (0.5 g L-1) and poly(vinyl alcohol) (PVA) (10
wt%) to form the precursor mixture of the A-GODs-embedded PVA film. For the fabrication
of white light emitting diode (LED), the mixture was dispensed on a violet (365 nm)-LED
chip and thermally dried at 60 °C for 24 h. The combination of the A-GODs-embedded PVA
film and violet-LED chip provides white light emissions, which are tunable through adjusting
the concentration of A-GODs in the PVA film. The device was characterized in a N2-filled
glove box with oxygen and water contents less than 1 ppm. The Commission International
d’Eclairage color coordinate of the light emission from the device was measured using a
Keithley 2400 source meter and a PR650 colorimeter.
Fig. S9 A-GODs as a phosphor for white-light emission. (a) A device consisting of an
A-GODs-embedded PVA film covering a violet (365 nm)-light emitting diode (LED) chip. (b)
White light emission from the device when the LED turned on. (c) The Commission
International d’Eclairage color coordinate for the white light emission shown in panel (b).
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