Laser-induced white-light emission from graphene ceramics–opening a band gap in graphene

ABSTRACT Recent theoretical and experimental studies have indicated the existence of a new stable phase of carbon with mixed sp2 and sp3 hybridized bonds—diaphite. Such a two-layered

structure with sp2/sp3 bonds may be observed after the photostimulation of highly oriented pyrolytic graphene with femtosecond laser pulses. This hidden multistability of graphene may be

used to create a semiconducting phase immersed in the semimetallic continuum, resulting in bandgap opening. We demonstrate that bandgap opening and light emission from graphene is possible

using continuous-wave laser beams with wavelengths from the visible (405 nm) to the near-infrared range (975 nm). We demonstrate that without the application of cooling, the effective

temperature of the emitting sample remains lower than 900 K, which is far below the value predicted by the theory of black-body radiation. Moreover, light emission from a graphene sample may

be observed at temperatures as low as 10 K. SIMILAR CONTENT BEING VIEWED BY OTHERS PLASMONICALLY ENHANCED MID-IR LIGHT SOURCE BASED ON TUNABLE SPECTRALLY AND DIRECTIONALLY SELECTIVE THERMAL

EMISSION FROM NANOPATTERNED GRAPHENE Article Open access 16 October 2020 ELECTROLUMINESCENCE AND ENERGY TRANSFER MEDIATED BY HYPERBOLIC POLARITONS Article 19 March 2025 DEEP-ULTRAVIOLET

ELECTROLUMINESCENCE AND PHOTOCURRENT GENERATION IN GRAPHENE/HBN/GRAPHENE HETEROSTRUCTURES Article Open access 08 December 2021 INTRODUCTION Because of its exceptional properties, graphene is

the focus of many extensive investigations. The two-dimensional crystal structure, linear energy dispersion and zero optical band gap of graphene, along with the presence of massless Dirac

quasiparticles, have successfully focused considerable scientific attention on this material, which theoretically should not exist.1 A number of studies have already reported many excellent

applications of graphene in various fields, e.g., new types of field-effect transistors,2 composite conductors3 and sensor applications.4,5 In addition to the interest in pristine graphene,

considerable scientific attention has also been devoted to the chemically derived hybrid known as graphene oxide, which exhibits unusual and tunable properties.6 As a chemical derivative,

graphene oxide possesses distinctly different properties than those of pristine graphene, which originate from the particular characteristics of the chemically reactive functional groups,

e.g., hydroxyl, epoxide, carbonyl and carboxyl groups, bound to the surface of grapheme.7 By controlling the sp2/sp3-hybridization ratio and the nature of the reactive groups, one is able to

control the optical and electrical properties of the resulting material.6 Recently, considerable scientific interest has also been devoted to studies of the white-light (WL) emission from

carbonaceous materials, using laser light or an electrical current as an excitation source. Incandescence experiments have been performed on a number of carbon structures, including carbon

nanotubes,8 fullerenes9,10 and graphene,11,12 which are being considered as materials for next-generation light sources. In particular, carbon nanotubes have been investigated for their

potential application as chemically stable thermal filaments in next-generation incandescent sources.13 However, although considerable efforts have been made in the development of

carbon-based devices,14 discussion of the WL emission from graphene is still severely lacking. It has previously been reported that pristine graphene exhibits no measurable light emission

under continuous-wave (CW) laser excitation; however, weak emission following the model of thermalized emission has been observed under femtosecond pulse excitation.15 The theory of

black-body radiation is naturally the first choice for the interpretation of the origin of light emissions from graphene and other carbonaceous materials.16 Various models have been proposed

to explain the origins of laser-induced incandescence, which is a complex phenomenon that involves laser absorption with the simultaneous emission of WL, which is responsible for cooling

the irradiated material.17 The observation of visible electroluminescence from multilayer graphene systems has also been reported by several authors.18 Biswas _et al_.19 have reported

tunable electroluminescence from planar graphene/SiO2 structures. Dong _et al_.20 have reported blue luminescence with a high quantum yield. Current-induced incandescent light emission has

also been observed in large-area graphene films by Yu and Dai.13 Recent studies of confined graphene systems have demonstrated the production of laser-excited WL emission from

edge-functionalized graphene quantum dots.21 To the best of our knowledge, we report here, for the first time, laser-induced WL emission from cooled (10 K) and moderate-temperature (<900 

K) graphene ceramics. The purpose of this work was to investigate the WL emission from graphene ceramics with regard to the potential application of these materials as alternative WL

sources. The distinctive features of this WL emission include the independence of the emission spectra with respect to the ambient temperature between 10 K and 300 K; the spectral

independence of the emission band with respect to the excitation wavelength, which results in Stokes and anti-Stokes emission; the nonlinear dependence of the process; and the

wavelength-dependent power threshold. We demonstrate that without cooling, the effective temperature of the emitting sample remains lower than 900 K, which is far below the value predicted

by the theory of black-body radiation. Moreover, it is shown that laser-induced WL emission from graphene ceramics is also clearly observed at cryogenic temperatures as low as 10 K. The

results are discussed in terms of transient photoinduced domain-like phase conversion in disordered graphene systems. MATERIALS AND METHODS PREPARATION OF THE GRAPHENE CERAMICS The graphene

ceramics (GCs) were prepared from commercial (CheapTubes.com. Cambridgeport, VT, USA) graphene nanoplatelets. The graphene nanoplatelets were characterized by surface areas of 600–750 m2 

g−1, the presence of 4–5 graphene layers with an average thickness of 8 nm, and a single-particle diameter of less than 2 μm (see Supplementary Information for transmission electron

microscopy images of the as-received graphene nanoplatelets). The GCs were fabricated in the form of pellets using the hot isostatic pressing method, which requires both an elevated

temperature and an isostatic pressure. As a first step, the graphene flakes were formed into pellets of 6 mm in diameter and 2 mm in thickness _via_ cold pressing at 0.2 GPa. The as-formed

pellets were then placed in a calcium carbonate (CaCO3) toroid and separated from the heating element by a thin layer of boron nitride. Each sample was then pressed at 8 GPa and heated to

500 °C for 1 min. As a final step, each GC sample was mechanically polished to remove the residual boron nitride powder and the topmost layers of graphene. Afterward, the sample was placed

in a vacuum chamber (see Supplementary Information for scanning electronic microscopy images of the GCs). SYNTHESIS OF LIYB0.99ER0.01P4O12 NANOTHERMOMETERS Erbium (Er3+)-doped lithium

ytterbium tetraphosphate nanocrystals were prepared _via_ a wet chemistry route. The starting materials for the synthesis were used without additional purification and were as follows:

(NH4)2HPO4 (POCH, 99.99%), erbium(III) oxide (Er2O3, 99.99%; Sigma-Aldrich, Poland), ytterbium(III) oxide (Yb2O3, 99.99%; Sigma-Aldrich) and Li2CO3 (POCH, 99.99%). Lanthanide ions were added

in the form of nitrates after prior dissolution of the corresponding oxides, e.g., Yb2O3 and Er2O3 were dissolved in concentrated nitric acid (HNO3). The (NH4)2HPO4 was dissolved in

deionized water and subsequently mixed with Li2CO3 and lanthanide nitrates containing appropriate amounts of Er3+ and Yb3+, resulting in a homogeneous solution. The LiYb0.99Er0.01P4O12

nanocrystals were obtained after the precipitation and transformation of the amorphous product into a crystalline product _via_ thermal treatment. The structural properties of the graphene

flakes were examined _via_ high-resolution transmission electron microscopy using a Philips CM20 SuperTwin transmission electron microscope, which provides a resolution of 0.25 nm at 200 kV

(see Supplementary Information). The luminescence spectra were measured using an Avantes AVS-USB2000 CCD spectrometer and a number of excitation laser sources, from the visible (VIS) up to

the near-infrared (NIR) regime: _λ_exc=975 nm, 808 nm, 514 nm, 488 nm, 476 nm and 405 nm. All graphene ceramics were measured in vacuum (10−3 hPa) and excited by a laser light focused to a

spot size of 1 mm. The temperature of the graphene ceramics was determined using LiYb0.99Er0.01P4O12 nanocrystals encrusted on the ceramic surface. The photoconductivity of the graphene

ceramics was measured _via_ the four-point method using four gold electrodes fixed with silver conducting paste. A 10-mA current source (Keithley 2002) was used in the experiment to measure

the voltage drop across the sample. RESULTS AND DISCUSSION The WL emission from the graphene ceramics was measured in oil-free vacuum (5×10−3 hPa). The samples were excited by a CW laser

beam focused to a spot of 1 mm in diameter. The laser-induced WL emission was investigated at a number of different excitation wavelengths, from the VIS up to the NIR range, i.e., at 476 nm,

488 nm, 514 nm, 808 nm and 975 nm. Representative spectra of the WL emission from the graphene ceramics upon irradiation at various excitation wavelengths are presented in Figure 1a. There

are several features of the data presented in Figure 1a that are worth noting. One distinctive feature of the data is its wide spectral range, extending over the VIS and NIR regions.

Notably, the emission occurs at energies higher than the energy of the exciting photons. This suggests that cascade multiphoton processes must be involved in this emission. At least three

characteristic maxima, at 1.97 eV (629 nm) and 1.83 eV (677 nm) and a shoulder at 1.68 eV (738 nm), may be identified in the emission band. It is worth noting that the presence of more than

one band maximum is in conflict with the theory of black-body radiation. A representative spectrum of black-body radiation for a temperature of _T_=4315 K is also presented for comparison.

No significant dependence of the broadband WL emission maxima on the excitation wavelengths was observed (Figure 1a). The peak maxima are located at nearly identical positions for each

wavelength, and only a slight broadening of the band is observed with decreasing excitation wavelength. The WL emission band is centered at approximately 1.87 eV (660 nm). The chromaticity

coordinates of the WL emission were calculated for all excitation wavelengths and are depicted in Figure 1b. Small shifts in the chromaticity coordinates were observed; however, all samples

were located in the white-orange region. Moreover, no particularly strong shifts in the emission-band maxima were observed for different excitation powers; however, it was observed that WL

emission from the graphene ceramics was a threshold process exhibiting supralinear behavior. The dependence of the laser-induced WL emission on the excitation light power is illustrated in

Figure 2. A representative plot of the WL emission excited at 975 nm for various laser powers is presented in Figure 2a. The nonlinear behavior of the excitation power, along with the

threshold point, is shown in Figure 2b for a number of excitation wavelengths. Once the threshold point is crossed, the WL emission increases in accordance with the power-law formula

(Equation (1)): where _I_WL is the intensity of the WL emission, _P_ is the power of the excitation laser light and _N_ is the order of the process. A monotonic dependence of the order of

the process on the excitation wavelength was observed (Figure 3). The lowest value of _N_=2.39 was observed for _λ_exc=405 nm, and the highest value of _N_=5.69 was observed for _λ_exc=975 

nm. For high-energy photons (3.06 eV), the WL emission appears to behave like Stokes emission, whereas for lower-energy excitation, the emission may be treated as an anti-Stokes process.

This finding indicates that the WL emission from graphene ceramics has its origin in multiphoton absorption. The total energy _E_tot of _N_ absorbed photons with energy _ħ_ωexc was nearly

identical for all investigated excitation wavelengths, _E_tot=_N_exc_ħ_ωexc. If we take the photon energy corresponding to the _λ_exc=975 nm excitation wavelength (1.27 eV) and multiply it

by a number of photons equal to 5.69, we obtain a value of 7.2 eV, which is similar to the value calculated for _λ_exc=808 nm (1.53 eV), which yields 7.9 eV. The calculated values of _E_tot

for the wavelengths in the VIS region, i.e., 405 nm (3.06 eV), 476 nm (2.60 eV), 488 nm (2.54 eV) and 514 nm (2.41 eV), are 8.5 eV, 7.9 eV, 8.4 eV and 8.9 eV, respectively. The values of

_E_tot calculated for the VIS excitation photons are higher than those for the infrared photons, which may be related to the different index of refraction for and better focusing of the

visible light. The important observation is that regardless of the wavelength of the incident laser light used in the experiment, the total energy _E_tot of absorbed photons that gave rise

to the WL emission was comparable and seems to have remained constant across the entire measured region. This behavior may be well understood by considering the nearly frequency-independent

absorption of graphene, which, for pristine graphene, is equal to the universal value of _πα_ (2.29%) determined by the fine-structure constant _α_=_e__2__/ħc_. A careful analysis of the

power dependence of the WL emission revealed the threshold behavior of the WL emission. It was observed that _P_th decreased with increasing photon energy. The value of _P_th was at its

lowest for blue-region photons (see the inset of Figure 3). This threshold behavior is characteristic of the multiphoton absorption processes responsible for photon avalanching and

photoionization. Because the WL emission from the graphene ceramics was observed only under a reduced atmospheric pressure, it was necessary to investigate the impact of the pressure

conditions on the relative intensity of the WL emission. The results for the dependence on the ambient pressure are presented in Figure 4a. The intensity of the WL emission increased by a

factor of approximately five upon the reduction of the pressure by over five decades to 5×10−3 hPa (Figure 4b). Although this increase is quite significant, much higher values have been

observed in measurements of similar processes in lanthanide-doped dielectrics, e.g., Yb3+:YAG22 and LiYbP4O1223 nanocrystals. The dependence of the WL emission on the ambient pressure offers

some clue as to the origin of the emission, which cannot simply be attributed to the contribution of functional groups, as for the emission of graphene oxide. The observed supralinear

dependence of the intensity on the ambient pressure may be predicted by the model of the radiative dissipation of energy24 (Equation (2)): where _P_ is the measured pressure and _I_0 is the

initial intensity at pressure _P_0. It is clear that because of the observed saturation region, the results remain in agreement with this model; however, the lower dependence on the ambient

pressure suggests that the convection process does not impact the emission intensity of our graphene ceramics as strongly as is observed in the dielectrics Yb3+:YAG and LiYbP4O12. The theory

of black-body radiation is naturally the first choice for the interpretation of the origin of the WL emission in graphene. Although the nature of the photoluminescence bands is in conflict

with that of black-body radiation, the question of the effective temperature of the sample is still one of fundamental interest. As can be calculated based on Planck’s theorem and the

characteristics of the WL emission, the temperature of the sample is expected to be approximately 4300 K. Moreover, according to the theorem, a blue-shift of the emission band _λ_max should

be observed with increasing sample temperature. However, as was previously demonstrated by the power-dependence measurements, no significant spectral shift was observed. This raises a

question regarding the true temperature of the emitting sample. The temperature of the emitting graphene ceramics was measured using the Er3+-doped LiYb0.99Er0.01P4O12 upconverting

nanocrystalline sensors encrusted on the surface of the emitting sample. The temperature sensing was achieved based on the well-known phenomenon that the ratio of the 4S3/2→4I15/2 and

2H11/2→4I15/2 transitions is related to the change in temperature. The emission intensity from the higher-lying state 2H11/2 depends on its population, which increases with temperature

following the Boltzmann relation (Equation (3)): where _A_ and _B_ are proportionality parameters, Δ_E_ is the energy difference between the indicated states, _T_ is the temperature and _k_B

is the Boltzmann constant. The energy gap between the states in the case of LiYb0.99Er0.01P4O12 is approximately 810 cm−1. The sample to be measured was placed in vacuum (5×10−3 hPa), and

the upconversion emission spectra were recorded (Figure 5a). Because the logarithm of the emission intensity ratio of 4S3/2→4I15/2 to 2H11/2→4I15/2 is a linear function of temperature, by

using the Boltzmann law, one is able to determine the temperature of nanocrystals subjected to laser excitation. Figure 5a presents the upconversion emission spectra of the

LiYb0.99Er0.01P4O12 nanocrystals encrusted on the graphene ceramic surface. Three characteristic _f_–_f_ fluorescence transitions of Er3+ located within the broadband WL emission of the

graphene ceramics are clearly observed. For the low-optical-power regime, only the Er3+ fluorescence signatures localized near approximately 520 nm, 540 nm and 650 nm were observed; these

signatures are associated with the 2H11/2→4I15/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions, respectively. With an increase in excitation power, the intensities of the UC transitions also

increased. The results revealed that even for a very high excitation power of 1.5 W at _λ_exc=975 nm, the temperature of the sample remained lower than 900 K, and for excitation powers lower

than 1 W, the temperature was lower than 700 K. To determine whether the WL emission from the graphene ceramics could also be observed at lower temperatures, additional experiments were

performed in a closed-cycle cryostat. The results are presented in Figure 5b. No particular temperature dependence was observed; indeed, the WL emission intensity remained nearly constant

across a wide range of temperatures, from 10 K to 300 K. It should be noted that similar experiments performed to investigate the anti-Stokes WL emission induced by an infrared laser in a

dielectric host in the form of LiNdP4O12 nanocrystals22 have demonstrated clear evidence of temperature dependence, with complete quenching of the emission at very low temperatures. These

results provide a very compelling reason to reconsider the interpretation of the origins of laser-induced WL emission from graphene. The photoelectrical response of the graphene ceramics

provides additional information regarding the origin of the WL emission. The time-dependent photoelectric response of the graphene ceramics for 975-nm laser excitation at various powers is

presented in Figure 6a. A linear dependence of the change in resistivity Δ_ρ_ on the excitation power was observed, with values up to Δ_ρ_≈0.5 mΩ cm. The time-dependent characteristics of

the process for two representative wavelengths of _λ_exc=405 nm and 975 nm are depicted in Figure 6b. The photo-effect associated with the interband transition is pronounced for 405 nm

excitation; however, thermo-electric effects contribute to the process, as is observed from the long saturation tail. The thermopower values of graphene ceramics may differ among samples,

depending on their preparation temperatures; at 300 K, these values may change from 6 µV K−1 to 20 µV K−1. A curve with a somewhat different character was observed for the 975-nm excitation

wavelength. Pronounced effects of thermal processes were also clearly observed. None of the curves was observed to follow the first-order rate law, implying that more than one process was

involved in the change in resistivity. The time constants of the processes under 975-nm excitation were estimated to be _τ_1=10.8 s and _τ_2=63.2 s. There are several considerations that may

be useful in forming any conclusions to be drawn regarding the origin of the WL emission from graphene ceramics. Because pristine graphene has no energy gap, no radiative emission is

observed under typical conditions of optical excitation. On the other hand, emission from thermalized electrons—incandescence—requires temperatures much higher than those measured in this

work. It was also demonstrated that the WL emission is a threshold process, which suggests that emission from graphene may be observed after a certain energy barrier is crossed (in our

experiments, _E_tot=_N_exc_ħ_ωexc≈8 eV), leading to the creation of transient, non-equilibrium phases with a different distribution of charge and a different electronic structure. It has

previously been demonstrated that non-equilibrium states in graphene involving a population of inverted dense Dirac fermions emerge during femtosecond pulse propagation.25 This observation

supports the concept of photoinduced transitions of sp2→sp3 hybridization in disordered phases such as graphene ceramics. Several studies have been published concerning light emission under

femtosecond light stimulation.26 However, the first reports of CW-excited hot luminescence were published by Chen _et al_.,27 who were studying inelastic light scattering in highly doped

graphene; WL emission from cold samples has never previously been reported. It is also worth noting that photoinduced phase transitions involving switching between anti-ferromagnetic and

magnetic states induced by femtosecond pulses _via_ strongly correlated spin-charge quantum excitation have also been demonstrated by Li _et al_.28 in non-carbonaceous compounds

(Pr0.7Ca0.3MnO3). Previous attempts to open a band gap in graphene have concentrated on the physical modification of the material, in which delocalization of _π_ bonds induces the creation

of the band gap.29,30 In this work, we propose a model of photoinduced phase transformation to explain the WL emission from CW-excited graphene ceramics.31 The photoinduced transition

process relies on a hidden multistability of the material, meaning that in addition to the true ground state, there are also hidden, so-called false ground states that are inaccessible

through thermal fluctuations but achievable through electronic excitation. A conceptual diagram of the photoinduced transition process is presented in Figure 7. Recent theoretical32,33,34,35

and experimental36,37 results have indicated the existence of a new stable phase of carbon with mixed sp2 and sp3 hybridized bonds—diaphite. In one such experiment, highly oriented

pyrolytic graphite was excited using a femtosecond laser (1.57-eV photon energy), leading to electron transfer between the _π_ and _π_* bands. Similar effects may also be induced _via_ CW

excitation, with two or three photons inducing a charge transfer from the _π_ band to the _π_* band and creating an electron–hole pair.35,38 A conceptual diagram of this mechanism is

presented in Figure 8. The latter process leads to the creation of transient localized states of electron-hole pairs. The electron-optical phonon coupling leads to graphene lattice

contraction, whereas unlocalized states contribute to the conduction band. Henceforth, a small amount of electronic energy is converted into kinetic energy of the lattice, leading to the

heating of the material. The overall process is a multiphoton process; however, as shown in Refs. 34, 39 and 40, a minimal diaphite domain may be created when the energy deposited in the

system exceeds 4.5 eV, which corresponds to only a few visible photons. The transformation is nonlinear because of the strong coupling between neighboring atoms in graphite sheets. It is

worth noting that the resulting new phase—diaphite—has already been observed to be a quasistable structure, with stability of up to a few days.36 As a result of the sp2→sp3 transition, a

band gap opens, resulting in the creation of a semiconducting phase immersed in the semimetallic continuum. Although this process has been observed in graphite, the theoretical

interpretation presented suggests that similar behavior should occur in all carbon systems with a linear band shape in the visible energy regime. Henceforth, the observation of phenomena of

this type is to be expected in bi- and trilayer graphene, as well. Our analysis suggests that the observed emission is purely electronic in nature. This conclusion explains both the heating

of the material (energy transfer _via_ free photo-generated carrier-phonon coupling) and the power-law dependence (threshold energy required for diaphite domain formation). The remaining

majority of unlocalized carriers will contribute to the ionization process. As stated above, CW excitation will lead to two types of carriers—localized and unlocalized. Coulomb repulsion

will induce rapid separation from the excited domain to the metallic continuum (Figure 8). As a result, the remaining carbon atoms will have a lower ionization potential because of the

appearance of excess charge in the system and _π_-bond expansion. Because the ionization potential in graphene is approximately 8 eV, multiphoton direct ionization will occur. Photoinduced

carriers will recombine with ionized carbons or contribute to the conduction _π_ band, thereby lowering the ionization potential. CONCLUSIONS Laser-induced WL emission from graphene ceramics

was investigated in this work. Intense WL emission centered at 650 nm and consisting of a number of subbands was observed. No significant dependence of the broadband WL emission maximum on

the excitation wavelength was observed. Laser-induced WL emission was observed at a number of different excitation wavelengths, from the VIS to the NIR range, i.e., at 476 nm, 488 nm, 514 

nm, 808 nm and 974 nm. It was also observed that the WL emission from graphene ceramics was a threshold process exhibiting supralinear behavior. It was observed that the intensity of the

laser-induced WL emission increased nonlinearly with increasing incident laser power, with a strong increase in intensity after a certain power threshold that could be well fitted using a

power law, _P__N_. The order of the process, _N_, decreased with increasing frequency of the incident laser light. Similarly, the excitation power threshold decreased with increasing

frequency of the incident laser light. The total energy _E_tot of _N_ absorbed photons with energy _ħ_ωexc remained nearly constant for all investigated excitation wavelengths,

_E_tot=_N_exc_ħ_ωexc≈8 eV. It was also demonstrated that the intensity of the WL emission was highly dependent on the ambient pressure. The highest intensity was observed at the lowest

pressure. The temperatures of the samples were also measured using LiYb0.99Er0.01P4O12 upconverting nanocrystals encrusted on the surfaces of the graphene ceramics. The results revealed that

even for a very high excitation power of 1.5 W at _λ_=975 nm, the temperature of the sample remained lower than 900 K, and for excitation powers lower than 1 W, the temperature was below

700 K. No dependence of the WL emission intensity on the sample temperature was observed, and WL emission was also observed at cryogenic temperatures as low as 10 K. This result provides

compelling evidence that even when the sample is hot, its temperature is still far too low to explain the emission according to the theory of thermalized electrons. Efficient photocurrent

was observed in the graphene ceramics. It increased linearly with increasing power of the incident laser light. A model of photoinduced, transient, domain-like sp2→sp3 phase transitions was

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Cooperative domain-type interlayer _sp_3 bond formation in graphite. _Phys Rev B_ 2010; 82: 035440. Article  ADS  Google Scholar  Download references ACKNOWLEDGEMENTS This work was supported

by Wroclaw Research Centre EIT+ within the framework of the project ‘The Application of Nanotechnology in Advanced Materials’—NanoMat (POIG.01.01.02-02-002/08) financed by the European

Regional Development Fund (Operational Programme Innovative Economy, 1.1.2). _NOTE: ACCEPTED ARTICLE PREVIEW ONLINE 19 NOVEMBER 2014_ AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Polish

Academy of Sciences, Institute of Low Temperatures and Structural Research, 50-422 Wroclaw, Poland Wieslaw Strek, Bartlomiej Cichy, Pawel Gluchowski, Lukasz Marciniak, Mikolaj Lukaszewicz 

& Dariusz Hreniak * Wroclaw University of Technology, Group of Chemical and Biochemical Processes, 50-370 Wroclaw, Poland Lukasz Radosinski Authors * Wieslaw Strek View author

publications You can also search for this author inPubMed Google Scholar * Bartlomiej Cichy View author publications You can also search for this author inPubMed Google Scholar * Lukasz

Radosinski View author publications You can also search for this author inPubMed Google Scholar * Pawel Gluchowski View author publications You can also search for this author inPubMed 

Google Scholar * Lukasz Marciniak View author publications You can also search for this author inPubMed Google Scholar * Mikolaj Lukaszewicz View author publications You can also search for

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Cichy. ADDITIONAL INFORMATION Note: Supplementary information for this article can be found on the _Light: Science & Applications'_ website. SUPPLEMENTARY INFORMATION SUPPLEMENTARY

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emission from graphene ceramics–opening a band gap in graphene. _Light Sci Appl_ 4, e237 (2015). https://doi.org/10.1038/lsa.2015.10 Download citation * Received: 16 July 2014 * Revised: 31

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SharedIt content-sharing initiative KEYWORDS * ceramics * graphene * photoluminescence * white light