Conduction Band Edge Research Articles

Composition-dependent band structure parameters and band-gap bowing effect in a caesium lead mixed halide system: a cyclic voltammetry investigation.

Cyclic voltammetry techniques have been employed to study the effect of halide substitution on the band edge parameters and band gap bowing effect in the case of CsPbX3 [X = I, Br, Cl] perovskite nanocrystals (PNCs). A series of compositions, viz. CsPbI3, CsPb(I-Br)3, CsPbBr3, CsPb(Br-Cl)3 and CsPbCl3, have been prepared by a hot injection method. From powder XRD and HR-TEM analysis, the formation of a highly crystalline, cubic phase of the perovskite having size in the range from 7-20 nm has been confirmed. Sharp peaks in the photoluminescence spectra suggest the formation of quantum dots with narrow-size distribution. The composition-dependent optical band gap (εopgap) for CsPbX3 displays a systematic shift towards shorter wavelengths from I to Br to Cl substitutions. The cyclic voltammetry investigation on the dispersion of PNCs in nonaqueous solvents yielded prominent cathodic and anodic peaks. These are correlated to conduction (e1) and valence band edge (h1) positions, respectively. The h1 has been decreased substantially with I to Br to Cl in CsPbX3. Meanwhile, e1 shows a marginal increase. The values derived from CV data demonstrated an excellent match with UVPS results, reported for a similar system. From these results, the quasi-particle gap (εqpgap) and exciton binding energy have been estimated for all the compositions. The negative band gap bowing effect noted in these PNCs is attributed to the size quantization effect. The band-edge parameters reported in this work will be valuable in matching these heterojunctions with suitable electron/hole transport materials for optimum device-performance.

Boosting Photocatalytic Water Splitting of Polymeric C60 by Reduced Dimensionality from Two-Dimensional Monolayer to One-Dimensional Chain.

The recent synthesis of monolayer fullerene networks (Hou, L., et al. Nature 2022, 606, 507) provides new opportunities for photovoltaics and photocatalysis because of their versatile crystal structures for further tailoring of electronic, optical, and chemical function. To shed light on the structural aspects of the photocatalytic water splitting performance of fullerene nanomaterials, we compare the photocatalytic properties of individual polymeric fullerene chains and monolayer fullerene networks from first-principles calculations. We find that the photocatalytic efficiency can be further optimized by reducing the dimensionality from two-dimensional (2D) to one-dimensional (1D). The conduction band edge of the polymeric C60 chain provides an external potential for the hydrogen reduction reaction much higher than that of its monolayer counterparts over a wider range of pH values, and there are 2 times more surface active sites in the 1D chain than in the 2D networks from a thermodynamic perspective. These observations identify the 1D fullerene polymer as a more promising candidate as a photocatalyst for the hydrogen evolution reaction in comparison to monolayer fullerene networks.

First principles phase diagram and electronic structure estimation of ZnO1-xSex photoanodes

Terminal solid solutions in the ZnO1−xSex system (0≤x≤0.15,0.95≤x≤1) exhibit extreme bandgap reduction attributable to band anti-crossing (BAC). In this work, we perform a theoretical investigation of alloying in this system (0≤x≤1). The temperature-composition phase diagram of ZnO1−xSex is obtained via first principles and cluster expansion-based Monte–Carlo simulations. For 0≤x≤0.05, a solid solution in the wurtzite structure and for 0.5≤x≤1, a solid solution in the sphalerite structure is obtained. The alloy system exhibits a miscibility gap in the range of 0.05≤x≤0.5. Only the solid solutions are seen to obey bandgap reduction predicted by BAC. The bandgap of the alloys, calculated using the Δ-sol method, shows a bowing behavior as predicted by the BAC model. Difference in the electronegativities of O and Se atoms in the lattice leads to hybridization of O-2p and Se-4p electronic states. Interaction between these electronic states also leads to a split in the valence band edge at the O-rich end and a split in the conduction band edge at the Se-rich end. The effective mass, estimated from the density of states, of holes at the O-rich end and that of electrons at the Se-rich end, increases with alloying. These fundamental insights should help in choosing suitable alloy compositions for optimal photocurrent density when these materials are used as photoanodes.

Trans-dimensionality of electron/hole channels in multilayer in-plane heterostructures comprising graphene and hBN superlattice

Abstract Using density functional theory, we investigated trilayer in-plane heterostructures consisting of graphene and hBN strips in terms of their interlayer stacking arrangements. The trilayer hBN/graphene superlattices possess flat dispersion bands at their band edges, the wave function distribution of which strongly depends on the interlayer stacking arrangement. The wave functions of the valence and conduction band edges of the trilayer heterostructure with AA’ stacking are distributed throughout the layers implying a two-dimensional carrier distribution. In contrast, we found one-dimensional carrier channels along the border between graphene and hBN for electrons and holes in the trilayer heterosheet with rhombohedral interlayer stacking. These unique carrier distributions are ascribed to the interlayer dipole moment arising from asymmetric arrangements of B and N atoms across the layers. Therefore, the trilayer in-plane heterostructures of graphene and hBN superlattice possess trans-dimensional carriers in terms of their interlayer stacking arrangement.

One-Pot Facile Synthesis of ZrO2-CdWO4: A Novel Nanocomposite for Hydrogen Production via Photocatalytic Water Splitting

ZrO2-based nanocomposites are highly versatile materials with huge potential for photocatalysis. In this study, ZrO2-CdWO4 nanocomposites (NC) were prepared via the green route using aqueous Brassica rapa leaf extract, and its photocatalytic water-splitting application was evaluated. Brassica rapa leaf extract acts as a reducing agent and abundant phytochemicals are adsorbed onto the nanoparticle surfaces, improving the properties of ZrO2-CdWO4 nanocomposites. As-prepared samples were characterized by using various spectroscopic and microscopic techniques. The energy of the direct band gap (Eg) of ZrO2-CdWO4 was determined as 2.66 eV. FTIR analysis revealed the various functional groups present in the prepared material. XRD analysis showed that the average crystallite size of ZrO2 and CdWO4 in ZrO2-CdWO4 was approximately 8 nm and 26 nm, respectively. SEM and TEM images suggested ZrO2 deposition over CdWO4 nanorods, which increases the roughness of the surface. The prepared sample was also suggested to be porous. BET surface area, pore volume, and half pore width of ZrO2-CdWO4 were estimated to be 19.6 m2/g. 0.0254 cc/g, and 9.457 Å, respectively. PL analysis suggested the conjugation between the ZrO2 and CdWO4 by lowering the PL graph on ZrO2 deposition over CdWO4. The valence and conduction band edge positions were also determined for ZrO2-CdWO4. These band positions suggested the formation of a type I heterojunction between ZrO2 and CdWO4. ZrO2-CdWO4 was used as a photocatalyst for hydrogen production via water splitting. Water-splitting results confirmed the ability of the ZrO2-CdWO4 system for enhanced hydrogen production. The effect of various parameters such as photocatalyst amount, reaction time, temperature, water pH, and concentration of sacrificial agent was also optimized. The results suggested that 250 mg of ZrO2-CdWO4 could produce 1574 µmol/g after 5 h at 27 °C, pH 7, using 30 vol. % of methanol. ZrO2-CdWO4 was reused for up to seven cycles with a high hydrogen production efficiency. This may prove to be useful research on the use of heterojunction materials for photocatalytic hydrogen production.

Exploring the electronic structure of BiVO4 thin films using energy-resolved electrochemical impedance spectroscopy

Bismuth vanadate (BiVO4) is a promising photoelectrochemical water-splitting semiconductor. This study focuses on elucidating the electronic structure of BiVO4 by analyzing energy-resolved electrochemical impedance spectroscopy (ER-EIS) data. The primary objective is to demonstrate the effectiveness of the ER-EIS, which is typically applied to organic semiconductors, in estimating the band edge positions of BiVO4 films deposited on FTO substrates.The impedance spectra analysis as a function of an applied overpotential permits an estimation of the density of states, where the limits correspond to the valence (VB) and conduction band (CB) edge positions that determine the redox reactions the semiconductor can promote. The energy difference between the CB and VB corresponds to the material's band gap (Eg). The calculated Eg using ER-EIS closely matches the reported optical properties of the material, and the energy positions of the VB and CB align with the reported values for BiVO4.

Ti-Modified Imogolite Nanotubes as Promising Photocatalyst 1D Nanostructures for H2 Production.

Imogolite nanotubes (INTs) are predicted as a unique 1D material with spatial separation of conduction and valence band edges but their large band gaps have inhibited their use as photocatalysts. The first step toward using these NTs in photocatalysis and exploiting the polarization-promoted charge separation across their walls is to reduce their band gap. Here, the modification of double-walled aluminogermanate INTs by incorporation of titanium into the NT walls is explored. The precursor ratio x = [Ti]/([Ge]+[Ti]) is modulated between 0 and 1. Structural and optical properties are determined at different scales and the photocatalytic performance is evaluated for H2 production. Although the incorporation of Ti atoms into the structure remains limited, the optimal condition is found around x = 0.4 for which the resulting NTs reveal a remarkable hydrogen production of ≈1500µmol g-1 after 5h for a noble metal-free photocatalyst, a 65-fold increase relative to a commercial TiO2-P25. This is correlated to a lowering of the recombination rate of photogenerated charge carriers for the most active structures. These results confirm the theoretical predictions regarding the potential of modified INTs as photoactive nanoreactors and pave the way for investigating and exploiting their polarization properties for energy applications.

Anisotropic properties of two-dimensional (2D) tin dihalide (SnX2, X = Cl, Br, I) monolayer binary materials

This paper investigated the electronic properties and photoresponse of two-dimensional SnX2 (X = Cl, Br, I) monolayer binary materials using computational techniques. The calculated band structure and density of states indicate that these are large band gap semiconducting materials with an indirect band gap. The studied chemical bonding mechanism shows the existence of the hybrid bonding of ionic and covalent bonds in these dihalide materials. The valence band (VB) and conduction band (CB) edge positions are also estimated, using the concept of electronegativity and band gap, to investigate the photocatalytic activity of SnX2. Next, we investigated the polarization and energy-dependent dielectric and optical functions along the crystallographic axes of these materials in the linear response approach of the perturbing incident oscillating light field. These materials exhibit an anisotropic behavior of these functions, especially in the high-energy visible and low-energy ultraviolet (UV) regions. The absorption of incident light photons is very fast in SnI2 than SnBr2 and SnCl2 in the low-energy UV region. It demonstrates the higher absorption coefficient and optical conductivity in Snl2. The obtained average static refractive index of SnCl2 is comparable to that of glass (1.5), showing its application as transparent material. The low reflection coefficient, less than 20%, makes them superior for antireflection coating materials in the infrared and visible regions. The prominent energy loss peaks show the existence of plasmon resonances in these materials. The most of losses occur in the UV region. The investigated electronic and photoresponse properties indicate that these Sn-based dihalide materials are excellent for electronic devices and optoelectronic applications. Also, the calculated VB and CB edge positions with respect to the normal hydrogen electrode show the favorable water-splitting capability of these materials.

ZIF-8 incorporated CeO2-CdS quantum dots @ 2D g-C3N4 nanosheets as a staggered type II heterojunction for decolouration of a set of dyes

Dye toxins, emitted by industries, pose a significant threat to living beings and aquatic life by absorbing light radiation and inhibiting the growth of essential bacteria and microbes, making their removal crucial for health of living beings and flora and fauna. This research endorsed a hydrothermal synthetic route for the photocatalyst CeO2/CdS/g-C3N4 @ZIF8 (or CCdGZ) fabrication to remove a set of hazardous dyes from wastewater streams. Corresponding Analytical methods evaluated the successfully developed CCdGZ photocatalyst's structural, morphological, and compositional properties. Powder X-ray photoelectron (PXRD) analysis showed the structural properties of CCdGZ and the quantum dot nature of the CeO2-CdS hybrid in the heterostructure with a crystallite size of 0.16 nm. The photocatalyst's optical responses were examined using UV–vis spectrophotometry and the UV-diffuse reflectance spectroscopy (UV-DRS) technique. Tauc's plot determined the energy band gap of the CCdGZ to be ∼2.64 eV, confirming a slight modification of the valence band (VB) and conduction band (CB) edges of the moieties CeO2, CdS, and g-C3N4. Thus, the heterostructure's moieties synergised to produce photocatalytic degradation. Under visible light irradiation, the photocatalyst CCdGZ photodegraded Victoria blue R (VBR) dye by 96.54% in 55 min. Photodegradation followed pseudo-first-order kinetics with a specific reaction rate of 0.06159 min−1 {coefficient of determination (R2) = 0.99847}. The corresponding TOC removal was 83.27%, while COD got reduced to 78.98% of its initial magnitude. Multiple reaction parameters, heterostructure reusability (over 89% efficient till the 5th run), the scavengers' experiment, inorganic ion effects, and water matrices were also evaluated. The study concludes with a photocatalytic reaction mechanism that explains the moieties' roles. This study designs a heterostructure photocatalyst that disintegrates emerging non-degradable organic pollutants in the UV–visible range, is recoverable, and has better photostability.

Enhancing perovskite solar cells: Tailoring the properties of Ti-doped MAPbBr3 for reduced recombination and improved efficiency

By using the sol-gel method, (0 %, 4 % and 6 %) Ti-doped MAPbBr3 films were deposited on FTO-glass substrates. XRD confirmed cubic structure of all films and the 4 % Ti-doped film has a large grain size of 80 nm. UV–Vis spectroscopy analysis confirmed that the 4 % Ti-doped film has low band gap energy of 2.36 eV, and a high refractive index of 2.62. The tuning of the conduction and valence band edges speeds up the movement of charges between the layers. The solar cells of these films have been fabricated with the geometry of glass/TiO2/Ti-MAPbBr3/spiro-OMeTAD/Au. The 4 % Ti-MAPbBr3 based cell showed high current density (9.15 mA/cm2), open circuit voltage (1.03 V), fill factor (0.7407), and efficiency (6.9804 %). EIS showed that the 4 % Ti-MAPbBr3 cell has an increased electron transfer rate and lowers the possibility of recombination at the TiO2/perovskite interface.

Dopant induced band convergence leading to high thermoelectric power factor in Mg2Sn

Band convergence is a common technique for enhancing the power factor of thermoelectric (TE) materials. This is usually achieved by solid solution formation in compounds having specific electronic band features. In this work, we show that a similar band convergence effect can be achieved in Mg2Sn by doping with small amounts of Bi. To identify this effect and the possible reason behind it, a detailed investigation of the electronic band structure (EBS) has been carried out using a recently developed multi-band refinement technique (MBRT). Nominal compositions of Mg2.2Sn1-xBix (x = 0,0.005, 0.01, 0.0125, 0.015, 0.02) have been synthesized by induction melting followed by compaction using uniaxial hot-pressing. Measurement of Seebeck coefficient (S), electrical conductivity (σ) and Hall Coefficient (RH) have been performed between 300K–700K and the data used for multi-band refinement. Results indicate changes in the inter-band separation of conduction bands with doping content and temperature. Significantly lower inter-band separation compared to reported undoped data is found even for the lowest doped composition, resulting in both conduction bands contributing to the power factor (S2σ). Further, for the heavily doped compositions (x = 0.0125, 0.015, 0.02) band-flipping between the conduction bands has been observed. Thus, the light conduction band is found to constitute the conduction band edge in the heavily doped compositions. This is contrary to the reported EBS of undoped Mg2Sn in which the heavy conduction band has a lower energy. Also, increasing temperature results in band convergence in the heavily doped compositions. A plausible cause for the band-flipping behaviour is provided based on merging of the impurity band with the light conduction band in heavily doped Mg2Sn. The band-flipping and the subsequent band convergence results in an even higher S2σ in the heavily doped compositions. The work highlights the beneficial influence of Bi doping on the TE properties of Mg2Sn and opens the possibility of utilizing dopants for achieving band convergence in TE materials.

Electrically Doped PNPN Tunnel Field-Effect Transistor Using Dual-Material Polarity Gate with Improved DC and Analog/RF Performance.

A new structure for PNPN tunnel field-effect transistors (TFETs) has been designed and simulated in this work. The proposed structure incorporates the polarity bias concept and the gate work function engineering to improve the DC and analog/RF figures of merit. The proposed device consists of a control gate (CG) and a polarity gate (PG), where the PG uses a dual-material gate (DMG) structure and is biased at -0.7 V to induce a P+ region in the source. The PNPN structure introduces a local minimum on the conduction band edge curve at the tunneling junction, which dramatically reduces the tunneling width. Furthermore, we show that incorporating the DMG architecture further enhances the drive current and improves the subthreshold slope (SS) characteristics by introducing an additional electric field peak. The numerical simulation reveals that the electrically doped PNPN TFET using DMG improves the DC and analog/RF performances in comparison to a conventional single-material gate (SMG) device.

Yellow TiO2 from titanium peroxo complexes: Verification of the visible light activity and a rational enhancement of its photocatalytic efficiency

It is widely believed that colored TiO2 materials (yellow, blue, black, violet, etc.) are visible-light active photocatalysts. In this article, we verify this claim with respect to the yellow TiO2 photocatalyst that has been synthesized using peroxo-titanium complexes formation route. The surface oxygen species, the electronic structure, the photoelectrochemical properties, and the photoactivity of yellow TiO2 have been investigated. FT-IR and XPS analysis confirms the presence of surface peroxo-species that caused the yellow color. Spectroelectrochemical measurements confirmed the absorption of violet light (400–430 nm). The reduced band gap energy (3.05 eV) has resulted from the anodic shift of both conduction and valence band edges by 0.30 and 0.15 eV, respectively. However, the wavelength-dependent photocurrent generation by yellow TiO2 in the presence of oxygen and under deaerated conditions proved that it does not contribute to the photoactivity enhancement in the visible region (λ > 400 nm). The proposed mechanism has shown that although the driving force at the oxidation side is theoretically improved, the reduction counterpart is parallelly weakened and the photoinduced electrons cannot efficiently reduce regular electron acceptors in aqueous systems (e.g., O2, H2O). Adding a low amount of a stronger electron acceptor (e.g., H2O2) into the system provides extra HO• radicals through the reductive mechanism. At higher concentrations of H2O2, the oxidation of H2O2 is more favorable. The hydroxylation of terephthalic acid via the oxidative and reductive pathway along with the bleaching of Congo Red indicates improved photocatalytic activity due to enhanced hydrogen peroxide activation. Although yellow TiO2 is active only upon UV light irradiation, this paper reports how to boost the photocatalytic activity of this material.

Theoretical Study of Doping in GaOOH for Electronics Applications

GaOOH, having a bandgap of 4.7–4.9 eV, can be regarded as one of several ultrawide-bandgap (UWBG) semiconductors, although it has so far mainly been used as a precursor material of Ga2O3. To examine the possibility of valence control and application in electronics, impurity levels in GaOOH are investigated using the first-principles density-functional theory calculation. The density values of the states of a supercell including an impurity atom are calculated. According to the results, among the group 14 elements, Si is expected to introduce a shallow donor level, i.e., a free electron is introduced. On the other hand, Ge and Sn introduce a localized state about 0.7 eV below the conduction band edge, and thus cannot act as an effective donor. While Mg and Ca can introduce a free hole and act as a shallow acceptor, Zn and Cd introduce acceptor levels away from the valence band. The transition metal elements (Fe, Co, Ni, Cu) are also considered, but none of them are expected to act as a shallow dopant. Thus, the results suggest that the carrier concentration can be controlled if Si is used for n-type doping, and Mg and Ca for p-type doping. Since GaOOH can be easily deposited using various chemical techniques at low temperatures, GaOOH will potentially be useful for transparent electronic devices.

Different temperature dependence of mobility in n- and p-channel 4H-SiC MOSFETs

The impact of interface state density (D it) near the conduction band edge (E C) and the VB edge (E V) on the field-effect mobility (μ FE) of NO- and N2-annealed n- and p-channel MOSFETs was investigated. With lowering the temperature, μ FE of n-channel MOSFETs decreased whereas μ FE increased in p-channel devices. Despite the comparable D it values near E C and E V, p-channel MOSFETs have less trapped carriers due to a deeper surface Fermi level caused by the larger effective masses of holes, resulting in smaller Coulomb scattering, and this may cause the different temperature dependence of μ FE in n- and p-channel MOSFETs.

Observations of very fast electron traps at SiC/high-κ dielectric interfaces

Very fast interface traps have recently been suggested to be the main cause behind poor channel-carrier mobility in SiC metal–oxide–semiconductor field effect transistors. It has been hypothesized that the NI traps are defects located inside the SiO2 dielectric with energy levels close to the SiC conduction band edge and the observed conductance spectroscopy signal is a result of electron tunneling to and from these defects. Using aluminum nitride and aluminum oxide as gate dielectrics instead of SiO2, we detect NI traps at these SiC/dielectric interfaces as well. A detailed investigation of the NI trap density and behavior as a function of temperature is presented and discussed. Advanced scanning transmission electron microscopy in combination with electron energy loss spectroscopy reveals no SiO2 at the interfaces. This strongly suggests that the NI traps are related to the surface region of the SiC rather than being a property of the gate dielectric.

Field-induced structural and orbital transformations leading to large bulk photovoltaic response in modified barium titanate

Ferroelectric systems are gaining importance in the perspective of capitalizing on their potential in energy applications. In particular, the ferroelectric photovoltaic effect is one of the attractive fields because of the reported above bandgap photovoltage. Although numerous efforts are being made to understand the ferroelectric photovoltaic mechanism, correlations among the structural, orbital, and photovoltaic characteristics, useful to engineer the system for applications, are rarely being investigated. Here, such correlations are established in electric field-induced studies carried out on the lead-free ferroelectric Ba0.875(Bi0.5Li0.5)0.125TiO3 system. Upon poling, x-ray diffraction studies reveal a twofold enhancement in the orthorhombic phase fraction at the expense of the tetragonal phase in comparison with the unpoled sample. The ex situ and in situ Raman studies demonstrate the field-induced changes in the structural characteristics. Furthermore, the Rayleigh analysis validates the field-induced lattice deformation in accordance with x-ray diffraction and Raman studies. Notably, the Ba0.875(Bi0.5Li0.5)0.125TiO3 sample exhibits anomalous open-circuit voltage (12 V) under the poling condition. To substantiate the experimental finding, density functional theory calculations are carried out. The theoretical calculations elucidate that the conduction band edge of the orthorhombic phase has a vital contribution from z character orbitals, which is further enhanced under poling to give rise to a higher shift current and, hence, a better photovoltaic response. However, the tetragonal phase's orbital characters are robust upon poling. Overall, these studies pave the way for designing ferroelectric systems for better photovoltaic properties.

Investigating charge traps in MoTe2 field-effect transistors: SiO2 insulator traps and MoTe2 bulk traps

Two-dimensional material-based field-effect transistors are promising for future use in electronic and optoelectronic applications. However, trap states existing in the transistors are known to hinder device performance. They capture/release carriers in the channel and lead to hysteresis in the transfer characteristics. In this work, we fabricated MoTe2 field-effect transistors on two different gate dielectrics, SiO2 and h-BN, and investigated temperature-dependent charge trapping behavior on the hysteresis in their transfer curves. We observed that devices with SiO2 back-gate dielectric are affected by both SiO2 insulator traps and MoTe2 intrinsic bulk traps, with the latter becoming prominent at temperatures above 310 K. Conversely, devices with h-BN back-gate dielectric, which host a negligible number of insulator traps, primarily exhibit MoTe2 bulk traps at high temperatures, enabling us to estimate the trap energy level at 389 meV below the conduction band edge. A similar energy level of 396 meV below the conduction band edge was observed from the emission current transient measurement. From a previous computational study, we expect these trap states to be the tellurium vacancy. Our results suggest that charge traps in MoTe2 field-effect transistors can be reduced by careful selection of gate insulators, thus providing guidelines for device fabrication.

Singlet-Triplet Energy Inversion in Carbon Nitride Photocatalysts.

Time-resolved EPR (TR-EPR) demonstrates the formation of well-defined spin triplet excitons in carbon nitride. This permits to experimentally probe the extent of the triplet wavefunction which delocalizes over several tri-s-triazine units. Analysis of the temperature dependence of the TR-EPR signal reveals the mobility of the triplet excitons. By employing monochromatic light excitation in the range 430-600 nm, the energy of the spin triplet is estimated to be ≈0.2 eV above the conduction band edge, proving that the triplet exciton lies above the corresponding singlet. Comparison between amorphous and graphitic forms establishes the singlet-triplet inversion as a general feature of carbon nitride materials.

Singlet‐Triplet Energy Inversion in Carbon Nitride Photocatalysts

AbstractTime‐resolved EPR (TR‐EPR) demonstrates the formation of well‐defined spin triplet excitons in carbon nitride. This permits to experimentally probe the extent of the triplet wavefunction which delocalizes over several tri‐s‐triazine units. Analysis of the temperature dependence of the TR‐EPR signal reveals the mobility of the triplet excitons. By employing monochromatic light excitation in the range 430–600 nm, the energy of the spin triplet is estimated to be ≈0.2 eV above the conduction band edge, proving that the triplet exciton lies above the corresponding singlet. Comparison between amorphous and graphitic forms establishes the singlet‐triplet inversion as a general feature of carbon nitride materials.