Predictive Design of Defect States in Hexagonal Boron Nitride for Telecommunication-Band Quantum Emission
Defect-based single-photon emitters (SPEs) in hexagonal boron nitride (h-BN) are promising platforms for integrated quantum photonics; however, the absence of identified emitters operating at telecom wavelengths remains a critical limitation for fiber-based quantum communication. Here, we investigate previously unexplored carbon- and silicon-based point defects in monolayer h-BN as SPE candidates using hybrid density functional theory, constrained excited-state relaxations, and a generating-function approach to photoluminescence. We compute zero-phonon-line (ZPL) energies, radiative lifetimes, Huang-Rhys (HR) factors, and photoluminescence lineshapes to screen optical performance. All defects are thermodynamically stable with negative formation energies, and five candidates exhibit moderate electron-phonon coupling (HR < 5), indicating narrow emission linewidths. These emitters span a broad spectral range from the visible to the telecom regime, including near-infrared C-based centers and, most notably, the Si2BVN defect, which is identified as the first point defect in monolayer h-BN predicted to support single-photon emission in the telecom C band (1554 nm). Vacancy-containing complexes possess spin-1/2 ground states, enabling spin-photon interfaces compatible with integrated photonic and cavity-based platforms. The combined analysis of ZPL energies, electron-phonon coupling, and radiative lifetimes provides concrete targets for experimental realization of spin-active single-photon emitters in h-BN from the visible to telecom wavelengths.