Luminescence lineshapes of nitrogen vacancy center in lonsdaleite and dual structure of diamond/lonsdaleite - a DFT study
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-05-02 |
| Journal | Scientific Reports |
| Authors | Khaled A Abdelghafar, Daniel ChoĂŻ, Khalid Askar |
| Institutions | Khalifa University of Science and Technology |
| Citations | 2 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study utilizes Density Functional Theory (DFT) to characterize the geometry, electronic structure, and luminescence properties of Nitrogen Vacancy (NV) centers in lonsdaleite (hexagonal diamond) and diamond/lonsdaleite dual structures, providing critical data for quantum material development.
- ZPL Validation: The calculated Zero-Phonon Line (ZPL) for the neutral NV0 center in the lonsdaleite phase (2.38 eV) strongly agrees with experimental data (2.32 eV) derived from meteorite impact samples, validating the computational model.
- Symmetry Reduction and Strain: Off-c-axis NV defects in lonsdaleite exhibit a reduction in symmetry from C3v to C1h, resulting in the splitting of excited states and localized strain, including a 0.003 A elongation in the C-N bond along the c-axis.
- Electron-Phonon Coupling (EPC): Off-c-axis defects demonstrate stronger EPC (higher Huang-Rhys factor) compared to on-c-axis defects, attributed directly to the reduced symmetry and increased geometry distortion.
- Phonon Side Band Dominance: Off-c-axis NV-1 configurations show the lowest ZPL weight (2.3-2.5%), confirming that their luminescence spectra are dominated by phonon side bands (PSB) rather than the sharp ZPL.
- Dual Structure Stability: The NV0 center located in the cubic diamond phase of the dual structure exhibits the highest ZPL weight (17.4%), suggesting the lowest geometrical distortion in that configuration.
- Quantum Material Foundation: The findings offer valuable insights into the intricate interplay between geometry, vibrational dynamics, and optical transitions, essential for engineering lonsdaleite-based NV centers for quantum technologies.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| ZPL (NV0, Dual Structure) | 2.38 | eV | Calculated for NV0 in the hexagonal phase (211L_D structure). |
| ZPL (NV0, Pure Lonsdaleite) | 2.29 | eV | Calculated using HSE06 hybrid functional. |
| ZPL (NV-1, Off-c-axis, Pure Lonsdaleite) | 2.04 | eV | Lowest calculated ZPL for pure lonsdaleite. |
| ZPL Weight (WZPL) (NV-1, Off-c-axis) | 2.49 | % | Lowest ZPL contribution among 4L_D configurations (hexagonal phase). |
| ZPL Weight (WZPL) (NV0, Diamond Phase) | 17.37 | % | Highest ZPL contribution in the 4L_D dual structure. |
| C-N Bond Elongation | 0.003 | A | Observed along the c-axis for off-c-axis NV-1 defects. |
| Plane-Wave Cutoff (Kinetic Energy) | 90 | Ry | Used for DFT geometry optimization. |
| Hartree-Fock Cutoff (Exact Exchange) | 180 | Ry | Used for HSE06 hybrid functional calculations. |
| Huang-Rhys (HR) Factor (Off-c-axis NV-1) | 3.77 | N/A | Pure lonsdaleite (HSE06), indicating strong Electron-Phonon Coupling. |
| Supercell Size (Pure Lonsdaleite) | 576 | Lattice Sites | (6x6x4) supercell used for phonon calculations. |
| Supercell Size (Dual Structure) | 647 | Atoms | (211L_D) structure used for realistic dual-phase modeling. |
Key Methodologies
Section titled âKey MethodologiesâThe study relied exclusively on advanced computational methods, primarily Density Functional Theory (DFT), to model defect properties and optical transitions.
- Ground State DFT: Electronic structure determined using Quantum ESPRESSO, employing the scalar-relativistic Optimized Norm-Conserving Vanderbilt Pseudopotential (ONCVPSP).
- Functional Selection: Geometry optimization utilized the Perdew-Burke-Ernzerhof (PBE) functional, while highly accurate ZPL calculations employed the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional.
- Geometry Optimization: Performed using the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm, targeting a total energy convergence threshold of 1 x 10-6 Ry and a force convergence threshold of 1 x 10-4 Ry/bohr.
- ZPL Calculation: Estimated by calculating the energy difference between the geometry-optimized ground state and the excited state. Fractional occupation (aey1.5e1.5) was applied to preserve excited state symmetry.
- Phonon Dynamics: Phonon dispersion and density of states calculated using the open-source Phonopy code, based on Atomic Force Constants derived from DFT.
- Luminescence Lineshape Modeling: The spectral density of electron-phonon coupling S(ħĎ) was calculated using the Pyphotonics post-processing code. The final luminescence lineshape L(ħĎ) was derived via Fourier transformation of the generating function G(t).
- Supercell Design: Large supercells (up to 980 lattice sites) were used to mitigate numerical errors associated with the charged supercell method (neutralizing background) and ensure convergence of the Huang-Rhys factor.
Commercial Applications
Section titled âCommercial ApplicationsâThe fundamental research on NV centers in lonsdaleite and dual-phase structures directly supports the advancement of next-generation quantum technologies and high-performance materials.
- Quantum Computing and Qubits: NV centers are leading candidates for solid-state qubits. Understanding their stability and optical properties in lonsdaleite provides a pathway for new quantum processor architectures.
- Quantum Sensing and Metrology: The atom-like behavior and sharp spectroscopic lines of NV centers are crucial for nanoscale imaging, magnetic field sensing, and temperature sensing applications.
- High-Performance Materials: Lonsdaleite is a metastable carbon allotrope known to outperform cubic diamond in mechanical properties. This research supports the engineering of robust, ultra-hard materials containing functional quantum defects.
- Optical Communication: Analogous to NV centers in SiC, if lonsdaleite NV centers can be tuned to emit in the infrared or telecom wavelengths, they could be utilized for quantum communication via optical fibers.
- Diamond Impact Sample Analysis: The model provides a theoretical framework to interpret complex luminescence data observed in natural diamond impact samples and meteorites, aiding in geological and planetary science research.