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Optically addressable spins in wide-bandgap semiconductors are a promising platform for exploring quantum phenomena. While colour centres in three-dimensional crystals such as diamond and silicon carbide were studied in detail, they were not observed experimentally in two-dimensional (2D) materials. Here, we report spin-dependent processes in the 2D material hexagonal boron nitride (hBN). We identify fluorescence lines associated with a particular defect, the negatively charged boron vacancy ( V B − ), showing a triplet ( S  = 1) ground state and zero-field splitting of ~3.5 GHz. We establish that this centre exhibits optically detected magnetic resonance at room temperature and demonstrate its spin polarization under optical pumping, which leads to optically induced population inversion of the spin ground state—a prerequisite for coherent spin-manipulation schemes. Our results constitute a step forward in establishing 2D hBN as a prime platform for scalable quantum technologies, with potential for spin-based quantum information and sensing applications. An ensemble of spins associated with an intrinsic defect of two-dimensional hexagonal boron nitride is shown to be optically addressable, allowing spin polarization of its triplet ground state and providing evidence of spin coherence.

Spin defects in solid-state materials are strong candidate systems for quantum information technology and sensing applications. Here we explore in details the recently discovered negatively charged boron vacancies (V B − ) in hexagonal boron nitride (hBN) and demonstrate their use as atomic scale sensors for temperature, magnetic fields and externally applied pressure. These applications are possible due to the high-spin triplet ground state and bright spin-dependent photoluminescence of the V B − . Specifically, we find that the frequency shift in optically detected magnetic resonance measurements is not only sensitive to static magnetic fields, but also to temperature and pressure changes which we relate to crystal lattice parameters. We show that spin-rich hBN films are potentially applicable as intrinsic sensors in heterostructures made of functionalized 2D materials. Spin defects in two-dimensional materials potentially offer unique advantages for quantum sensing in terms of sensitivity and functionality. Here, the authors demonstrate the use of spin defects in hexagonal boron nitride as sensors of magnetic field, temperature and pressure, and show that their performance is comparable or exceeds that of existing platforms.

Molecules present a versatile platform for quantum information science 1 , 2 and are candidates for sensing and computation applications 3 , 4 . Robust spin-optical interfaces are key to harnessing the quantum resources of materials 5 . To date, carbon-based candidates have been non-luminescent 6 , 7 , which prevents optical readout via emission. Here we report organic molecules showing both efficient luminescence and near-unity generation yield of excited states with spin multiplicity  S > 1. This was achieved by designing an energy resonance between emissive doublet and triplet levels, here on covalently coupled tris(2,4,6-trichlorophenyl) methyl-carbazole radicals and anthracene. We observed that the doublet photoexcitation delocalized onto the linked acene within a few picoseconds and subsequently evolved to a pure high-spin state (quartet for monoradical, quintet for biradical) of mixed radical–triplet character near 1.8 eV. These high-spin states are coherently addressable with microwaves even at 295 K, with optical readout enabled by reverse intersystem crossing to emissive states. Furthermore, for the biradical, on return to the ground state the previously uncorrelated radical spins either side of the anthracene shows strong spin correlation. Our approach simultaneously supports a high efficiency of initialization, spin manipulations and light-based readout at room temperature. The integration of luminescence and high-spin states creates an organic materials platform for emerging quantum technologies. We report organic molecules showing both efficient luminescence and near-unity generation yield of excited states with high spin multiplicity, simultaneously supporting a high efficiency of initialization, spin manipulations and light-based readout at room temperature.

We report the first demonstration of a semiconductor maser based on silicon vacancies (V Si ) in 4H-silicon carbide (SiC). Using an active feedback loop, we enhance the resonator’s quality factor, enabling continuous-wave maser operation even above room temperature. We analyzed the SiC maser as a high-performance preamplifier, with measured gain exceeding 10 dB at 110 K and simulations suggesting potential amplification beyond 30 dB. Leveraging the small zero-field splitting of V Si , the device can also function as an optically pumped microwave photon absorber, reducing the resonator’s mode temperature by 40 K relative to the environment. Additionally, the maser’s ultranarrow linewidth supports highly sensitive magnetometry, achieving a nine-order-of-magnitude improvement in contrast-to-linewidth ratio over electrical and optical detection of magnetic resonance. This results in an estimated magnetic field sensitivity of 20 pT/√Hz at room-temperature based on the relative intensity noise of the excitation laser. These results underscore the potential of SiC to reshape room-temperature maser technologies, and lay the groundwork for future development of compact, electrically driven maser diodes. The first semiconductor maser in silicon carbide is demonstrated, achieving continuous-wave operation above room temperature with high gain, microwave mode cooling, and ultrasensitive magnetometry, enabling compact, scalable maser technologies.

Stability is now a critical factor in the commercialization of organic photovoltaic (OPV) devices. Both extrinsic stability to oxygen and water and intrinsic stability to light and heat in inert conditions must be achieved. Triplet states are known to be problematic in both cases, leading to singlet oxygen production or fullerene dimerization. The latter is thought to proceed from unquenched singlet excitons that have undergone intersystem crossing (ISC). Instead, we show that in bulk heterojunction (BHJ) solar cells the photo-degradation of C 60 via photo-oligomerization occurs primarily via back-hole transfer (BHT) from a charge-transfer state to a C 60 excited triplet state. We demonstrate this to be the principal pathway from a combination of steady-state optoelectronic measurements, time-resolved electron paramagnetic resonance, and temperature-dependent transient absorption spectroscopy on model systems. BHT is a much more serious concern than ISC because it cannot be mitigated by improved exciton quenching, obtained for example by a finer BHJ morphology. As BHT is not specific to fullerenes, our results suggest that the role of electron and hole back transfer in the degradation of BHJs should also be carefully considered when designing stable OPV devices. The commercialisation of organic photovoltaic technology calls for research on material degradation mechanisms. Ramirez et al. show that triplet excitons produced by back charge transfer can significantly impact the photo-stability of fullerene-based devices even in the absence of water and oxygen.

Semiconducting single-walled carbon nanotubes (SWNTs) are considered as building blocks for novel optoelectronic and photonic devices. Energy transport, dissipation and nonlinear optical properties of such devices depend critically on the dynamics of singlet and triplet excitons. However, little is known about triplet excitons in SWNTs despite their important role in photovoltaic, photoelectric and other applications. We present pump–probe and spin-sensitive photoluminescence studies of semiconducting SWNTs that allow the determination of the quantum yield of triplet formation (5 ± 2%), the triplet lifetime (30 ± 10 µs) and the triplet exciton size (0.65 nm). Triplet–triplet annihilation is also found to induce delayed fluorescence. The power-law decay of pump–probe and time-resolved photoluminescence signals is characteristic of diffusion-limited annihilation in one-dimensional systems and allows an estimation of the triplet diffusion constant of 0.1 cm 2  s −1 . This work suggests that exciton annihilation in SWNTs is reduced by one-dimensional confinement of diffusive exciton motion. Little is known about triplet excitons in semiconducting single-walled nanotubes, despite their importance in various applications. The pump–probe and spin-sensitive photoluminescence of such nanotubes is studied, and the quantum yield of triplet formation, triplet lifetime and triplet exciton size are found to be 5 ± 2%, 30 ± 10 µs and 0.65 nm, respectively.

A strategy for increasing the conversion efficiency of organic photovoltaics has been to increase the V OC by tuning the energy levels of donor and acceptor components. However, this opens up a new loss pathway from an interfacial charge transfer state to a triplet exciton (TE) state called electron back transfer (EBT), which is detrimental to device performance. To test this hypothesis, we study triplet formation in the high performing PTB7:PC 71 BM blend system and determine the impact of the morphology-optimizing additive 1,8-diiodoctane (DIO). Using photoluminescence and spin-sensitive optically detected magnetic resonance (ODMR) measurements at low temperature, we find that TEs form on PC 71 BM via intersystem crossing from singlet excitons and on PTB7 via EBT mechanism. For DIO blends with smaller fullerene domains, an increased density of PTB7 TEs is observed. The EBT process is found to be significant only at very low temperature. At 300 K, no triplets are detected via ODMR and electrically detected magnetic resonance on optimized solar cells indicates that TEs are only present on the fullerenes. We conclude that in PTB7:PC 71 BM devices, TE formation via EBT is impacted by fullerene domain size at low temperature, but at room temperature, EBT does not represent a dominant loss pathway.

Background Even though the post-operative outcome varies greatly among patients with nodal positive colon cancer (UICC stage III), personalized prediction of systemic disease recurrence is currently insufficient. We investigated in a retrospective setting whether genetic and immunological biomarkers can be applied for stratification of distant metastasis occurrence risk. Methods Eighty four patients with complete resection (R0) of stage III colon cancer from two clinical centres were analysed for genetic biomarkers: microsatellite instability, oncogenic mutations in KRAS exon2 and BRAF exon15, expression of osteopontin and the metastasis-associated genes SASH1 and MACC1. Tumor-infiltrating CD3 and CD8 positive T-cells were quantified by immunocytochemistry. Results were correlated with outcome and response to 5-FU based adjuvant chemotherapy, using Cox’s proportional hazard models and integrative two-step cluster analysis. Results Distant metastasis risk was significantly correlated with oncogenic KRAS mutations ( p  = 0.015), expression of SASH1 ( p  = 0.016), and the density of CD8-positive T-cells ( p  = 0.007) in Kaplan-Meier analysis. Upon multivariate Cox-regression analysis, KRAS mutation ( p  = 0.008) and density of CD8-positive TILs ( p  = 0.009) were retained as prognostic parameters for metachronous distant metastasis. Integrative two-step cluster analysis was used to combine all genetic markers, allowing stratification of patient subgroups. Post-operative distant metastasis risk ranged from 31% (low-risk) to 41% (intermediate), and 57% (high-risk) ( p  = 0.032). Increased expression of osteopontin ( p  = 0.019) and low density of CD8-positive T-cells ( p  = 0.043) were significantly associated with unfavourable response to 5-FU. Conclusions Integrative biomarker analysis allows stratification of stage III colon cancer patients for the risk of metastatic disease recurrence and may indicate response to 5-FU. Thus, biomarker analysis might facilitate the use of adjuvant therapy for high risk patients.

p-Phenylenediamine was oxidized with p-benzoquinone in the aqueous solutions of methanesulfonic acid (MSA). The conductivity of the products increased with increasing concentration of MSA from 1.5 × 10−12 S cm−1 in 0.1 M MSA up to 3.4 × 10−4 S cm−1 in 5 M MSA. The low-molecular-weight products are basically composed of one p-benzoquinone and two p-phenylenediamine molecules. Their molecular structure is discussed on the basis of mass, Fourier-transform infrared, Raman, NMR and electron paramagnetic resonance (EPR) spectroscopies. The formation of 2,5-di(p-phenylenediamine)-p-benzoquinone protonated with methanesulfonic acid best complies with the information provided by spectroscopic techniques. Its conversion to hydroquinone tautomer explains the formation of unpaired spins observed by EPR and their potential contribution to the conduction.

We report the first demonstration of a semiconductor maser based on silicon vacancies (VSi) in 4H-silicon carbide (SiC). Using an active feedback loop, we enhance the resonator's quality factor, enabling continuous-wave maser operation even above room temperature. We analyzed the SiC maser as a high-performance preamplifier, with measured gain exceeding 10 dB at 110 K and simulations suggesting potential amplification beyond 30 dB. Leveraging the small zero-field splitting of VSi, the device can also function as an optically pumped microwave photon absorber, reducing the resonator's mode temperature by 40 K relative to the environment. Additionally, the maser's ultranarrow linewidth supports highly sensitive magnetometry, achieving a nine-order-of-magnitude improvement in contrast-to-linewidth ratio over electrical and optical detection of magnetic resonance. This results in an estimated magnetic field sensitivity of 20 pT/sqrt(Hz) at room-temperature based on the relative intensity noise of the excitation laser. These results underscore the potential of SiC to reshape room-temperature maser technologies, and lay the groundwork for future development of compact, electrically driven maser diodes.