Defect-enabled single-photon emitters in two-dimensional materials such as hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMDCs) have emerged as promising candidates for quantum photonic applications. These emitters exhibit key properties such as high brightness, room-temperature operation, and wavelength tunability, making them attractive for integration into scalable quantum technologies. This article examines the emission stability, wavelength tunability, and photonic integration of these defects while contrasting their performance with diamond nitrogen-vacancy (NV) centers.

Single-photon emitters in hBN and TMDCs are typically associated with point defects, such as vacancies, antisite defects, or impurity complexes. In hBN, carbon-related defects and boron vacancies are among the most studied, emitting in the visible to near-infrared range. TMDCs, such as MoS2 and WSe2, host chalcogen vacancies or strain-induced defects that exhibit sharp photoluminescence lines. Unlike diamond NV centers, which require cryogenic temperatures for optimal performance, many 2D material emitters operate efficiently at room temperature due to reduced phonon coupling and strong exciton localization.

Emission stability is a critical metric for practical applications. hBN defects demonstrate high photostability with blinking suppression under optimized excitation conditions. Studies report continuous operation for hours without significant degradation, attributed to the inert nature of hBN and the shielding effect of its layered structure. TMDC emitters, however, show greater susceptibility to environmental factors such as oxidation and adsorbates, leading to fluctuations in emission intensity. Encapsulation with hBN or other inert layers improves stability by minimizing surface interactions. In contrast, diamond NV centers exhibit excellent stability but often require complex surface treatments to mitigate charge noise.

Wavelength tunability is another distinguishing feature of 2D material emitters. Strain engineering, electric fields, and substrate interactions enable precise control over emission energies. In hBN, defects can be tuned over a range exceeding 100 meV via applied strain or local dielectric environment modifications. TMDC defects exhibit even broader tunability, with shifts up to 200 meV achievable through electrostatic gating or mechanical deformation. This flexibility is advantageous for matching emitter wavelengths to photonic cavity resonances or other quantum systems. Diamond NV centers, while stable, lack comparable tunability due to their rigid crystal lattice.

Integration with photonic cavities is essential for enhancing emission rates and enabling quantum networking. hBN emitters couple efficiently to plasmonic nanocavities and dielectric resonators, with reported Purcell enhancements exceeding a factor of 10. The sub-nanometer thickness of hBN allows for near-field coupling without significant optical losses. TMDC emitters also benefit from cavity integration, but their performance is more sensitive to placement accuracy due to their atomic-scale emission sites. Both materials outperform diamond NV centers in terms of ease of integration, as the latter often require elaborate nanofabrication techniques to embed within optical structures.

A comparison of key metrics highlights the advantages of 2D material emitters:

| Property | hBN Defects | TMDC Defects | Diamond NV Centers |
|------------------------|-------------------|-------------------|--------------------|
| Operating Temperature | Room temperature | Room temperature | Cryogenic preferred|
| Emission Tunability | High (100+ meV) | Very High (200 meV)| Low |
| Photostability | Excellent | Moderate | Excellent |
| Cavity Integration | Straightforward | Moderate | Challenging |

Despite these strengths, challenges remain for 2D material emitters. Spectral diffusion, caused by charge fluctuations in the surrounding environment, can degrade emission linewidths. Advances in defect engineering and encapsulation techniques are mitigating this issue. Additionally, the deterministic creation of defects with uniform properties remains an ongoing research focus.

In summary, defect-enabled single-photon emitters in hBN and TMDCs offer compelling advantages over traditional diamond NV centers, particularly in terms of room-temperature operation, wavelength tunability, and photonic integration. Continued progress in defect control and device engineering will further solidify their role in quantum technologies.