Infrared quantum emission and its tuning from boron-nitride nanotube fluors

Point-defected 2-D hBN based quantum light sources are highly regarded as promising candidates for emerging quantum photonic technologies. However, achieving tunable defect-induced optical emission within the infrared telecommunication window for low-loss, long-distance quantum communication continues to be a major challenge. In this context, Boron nitride nanotubes (BNNTs), owing to their unique one-dimensional geometry and defect engineering capability, offer a potential platform for exploring such tunable optical transitions. In this work, first-principles density functional theory (DFT) calculations were employed to investigate defect-induced optical transitions in single-walled BNNTs containing intrinsic point defects. The calculations predict that CB defect centers can exhibit tunable near-infrared zero-phonon-line (ZPL)-like emission features spanning approximately 1000–2000 nm by varying the nanotube diameter from ~ 0.8 to ~ 0.4 nm (zigzag (10,0) to (5,0)) without external tuning. Further modulation of these predicted emission energies is predicted to occur under externally applied uniaxial strain and axial electric fields. For the CB defect in the (5,0) BNNT, the calculated emission wavelength is predicted to be tunable from approximately 2000 nm to 2300 nm under uniaxial strain and from approximately 2000 nm to 3400 nm under an applied electric field. Similar strain-induced tunability is predicted for other defect configurations, including CN, CNVB, and VB, with calculated emission ranges extending from approximately 980–4000 nm and 1800–2300 nm for the CNVB and VB defects, respectively. These predicted emission modulations are anticipated to arise from subtle modifications of the local defect environment induced by nanotube curvature, externally applied strain, and electric-field-induced changes in the defect electronic structure. These results suggest that defect-engineered BNNTs may provide a promising platform for tunable defect-based optical emitters spanning important near- and mid-infrared spectral regions, including portions of the optical communication window such as the C- and L-bands and beyond, which may support future optical communication technologies and could potentially extend operation into the mid-infrared atmospheric window for free-space optical (FSO) communication. While the present predictions provide an insight into defect-induced optical transitions in BNNTs, further advanced excited-state calculations and experimental validation will be necessary to confirm their quantum emission characteristics.