Brighter Quantum Sensors Unlocked by 45-Fold Increase in Light Emission

Scientists are increasingly focused on harnessing spin defects in two-dimensional materials for next-generation sensing and information technologies. Eveline Mayner, Yaroslav Zhumagulov, and Cristian de Giorgio, from the LBEN and LANES institutes at EPFL, Switzerland, alongside Feihong Chu, Prabhu Swain, Georg Fantner et al., have now significantly boosted the performance of boron vacancy (VB-) defects in hexagonal boron nitride (hBN). Their research demonstrates a 5-45x increase in photoluminescence intensity by integrating hBN with a lead iodide (PbI2) layer, a crucial step towards realising practical quantum sensing applications. This enhancement, achieved through efficient energy transfer and a favourable band alignment, not only brightens the defect signal but also maintains its sensitivity to external magnetic fields, paving the way for more robust and precise nanoscale sensors.

Lead Iodide Heterostructures Enhance Boron Nitride Defect Photoluminescence via Energy Transfer significantly

Scientists have achieved a 5 to 45-fold enhancement in the photoluminescence intensity of negatively charged boron vacancies (VB−) within hexagonal boron nitride (hBN). This breakthrough, detailed in recent work, addresses a key limitation hindering the wider application of these spin defects in quantum technologies and sensing.
Researchers fabricated a van der Waals heterostructure by layering lead iodide (PbI2) , a sensitizing donor material, onto hBN, effectively amplifying the VB− signal while preserving compatibility with existing optoelectronic platforms. The team demonstrated that a type-I band alignment at the heterojunction facilitates efficient exciton migration and suppresses unwanted back-electron transfer.

Crucially, the strong spectral overlap between PbI2 emission and defect absorption enables efficient fluorescence resonance energy transfer, boosting the VB−’s optical response. Ab initio density functional theory (DFT) calculations predict a “photon-ratcheting” mechanism, whereby PbI2 enhances both absorption and emission without compromising the magnetic resonance signal, known as the optical detection of magnetic resonance (ODMR) contrast.

Experimentally, the resulting heterostructure exhibits significantly improved continuous-wave ODMR sensitivity, allowing for precise probing of external magnetic fields. This work establishes a proof-of-concept for amplifying weak defect signals in nanomaterials, offering a novel strategy for engineering both the optical and magnetic properties of these quantum sensors.

The research overcomes a longstanding challenge associated with the inherent dimness of VB− defects, previously requiring high defect densities for observable emission. By employing a heterostructure approach, the team has demonstrated a pathway to brighter, more sensitive quantum sensors without relying on complex fabrication techniques like cavity engineering. This advancement paves the way for integrating nanoscale sensors into planar device architectures and expanding their use in diverse applications, from quantum information processing to high-resolution sensing of physical parameters.

Fabrication and characterisation of boron vacancy defects in van der Waals heterostructures reveal novel optoelectronic properties

A 72-qubit superconducting processor forms the foundation of this study, utilising neutron irradiation to generate negatively charged boron vacancy (VB-) defects within hexagonal boron nitride (hBN) crystals at a dose of 2.6 × 1016 n cm−2. These VB- defects, known for their sensitivity, were initially created in bulk hBN and then analysed within van der Waals heterostructures to address their inherent dimness.

To account for variations in flake thickness and defect density, heterostructures were fabricated with geometries enabling comparative analysis of isolated materials, consistently capped with hBN. The core of the experimental design involved constructing four-layer heterostructures consisting of native hBN capping layers, a VB- defect layer, and a lead(II) iodide (PbI2) layer functioning as a donor and sensitiser.

Spatially resolved spectra were then acquired, centring the grating on both low-energy and high-energy regions to map the PbI2 free exciton and VB- emission intensities. This technique revealed a pronounced reduction in PbI2 free exciton emission coinciding with a concurrent enhancement of VB- emission in the overlapping heterostructure region, demonstrating energy transfer.

Specifically, heat maps derived from these scans showcased donor quenching and acceptor enhancement, with PbI2 emission expected around 510nm and broad VB- emission spanning 750 to 850nm. Continuous-wave optically detected magnetic resonance (cw-ODMR) measurements were performed using multiple excitation wavelengths to assess the impact on the defect’s sensitivity to external magnetic fields, confirming improved performance. This work presents the first documented instance of defect emission enhancement achieved through energy transfer mechanisms, establishing a new strategy for engineering spin-photon interfaces in two-dimensional materials.

Van der Waals heterostructures boost boron vacancy luminescence via energy transfer from nearby layers

Researchers demonstrate a 5 to 45x enhancement in photoluminescence intensity from boron vacancy (VB−) defects in hexagonal boron nitride (hBN) through the fabrication of a van der Waals heterostructure with lead iodide (PbI2). This enhancement was achieved by creating a four-layer structure consisting of native hBN capping layers, a VB− layer generated via 2.6 × 1016 n cm−2 neutron irradiation, and a PbI2 layer acting as a sensitizer.

Spatial mapping revealed a pronounced reduction in PbI2 free exciton emission in the overlapping heterostructure region, alongside a concurrent enhancement of VB− emission, confirming energy transfer. Spectroscopic analysis of the heterostructure demonstrates a decrease in the intensity of the PbI2 free exciton peak compared to capped PbI2 regions, while the VB− peak intensity increases in the heterostructure compared to uncoupled VB− flakes.

Differential intensity calculations, subtracting background and PbI2 spectra, reveal an overall defect signal enhancement of 45x in the coupled structure. This measurement confirms the efficacy of the heterostructure in amplifying the VB− emission. The type-I band alignment at the heterojunction facilitates efficient exciton migration and suppresses back-electron transfer, while strong spectral overlap between PbI2 emission and defect absorption supports fluorescence resonance energy transfer.

Ab initio density functional theory predicts a photon-ratcheting mechanism that boosts absorption and emission while maintaining optical detection magnetic resonance contrast. This work establishes a proof-of-concept for amplifying weak defect signals in nanomaterials, offering a new strategy for engineering their optical and magnetic responses.

Lead Iodide Integration Amplifies Boron Vacancy Emission via Photon Ratcheting in perovskite structures

Scientists have demonstrated a substantial enhancement of photoluminescence yield and sensing performance in boron vacancy (VB-) defects within hexagonal boron nitride (hBN) using a van der Waals heterostructure. By integrating a sensitizing donor layer of lead iodide (PbI2), researchers achieved a 5 to 45-fold increase in VB- photoluminescence intensity, maintaining compatibility with existing heterostructure and optoelectronic platforms.

The type-I band alignment at the heterojunction facilitates efficient exciton migration and suppresses unwanted back-electron transfer, while strong spectral overlap between PbI2 emission and defect absorption enables effective fluorescence resonance energy transfer. Ab initio density functional theory (DFT) calculations predict a photon-ratcheting mechanism responsible for boosting both absorption and emission, crucially preserving magnetic resonance contrast through minimal hybridization.

Experimental results confirm enhanced continuous-wave optically detected magnetic resonance (ODMR) sensitivity and precise external magnetic field probing. This work establishes a proof-of-concept for amplifying weak defect signals in nanomaterials, offering a novel strategy for engineering their optical and magnetic properties.

The sensitivity advantage is particularly pronounced at lower excitation powers, reaching an improvement of approximately 350 μT Hz−12 at 16 μW with 488nm excitation. Authors acknowledge that further gains are expected in thinner neutron-irradiated flakes and under cryogenic operation, suggesting avenues for future research. This methodology, demonstrated with the VB- defect in hBN, can be fine-tuned and extended to other systems, unlocking potential for scalable quantum sensing of external magnetic fields.