# Carbon dimer defect as a source of the 4.1 eV luminescence in hexagonal boron nitride

## TL;DR

This paper identifies the carbon dimer defect in hexagonal boron nitride as the source of the 4.1 eV luminescence band, using first-principles calculations to match experimental data and elucidate the defect's optical properties.

## Contribution

It provides a detailed first-principles analysis linking the carbon dimer defect to the luminescence in hexagonal boron nitride, offering insights into the defect's electronic structure and optical behavior.

## Key findings

- Calculated zero-phonon line energy of 4.3 eV closely matches experimental 4.1 eV.
- Deduced Huang-Rhys factor of approximately 2.0 indicates modest electron-phonon coupling.
- Radiative lifetime of 1.2 nanoseconds aligns with experimental observations.

## Abstract

We propose that the carbon dimer defect in hexagonal boron nitride gives rise to the ubiquitous narrow luminescence band with a zero-phonon line of 4.08 eV (usually labeled the 4.1 eV band). Our first-principles calculations are based on hybrid density functionals that provide a reliable description of wide band-gap materials. The calculated zero-phonon line energy of 4.3 eV is close to the experimental value, and the deduced Huang-Rhys factor of ${S \approx 2.0}$, indicating modest electron-phonon coupling, falls within the experimental range. The optical transition occurs between two localized $\pi$-type defects states, with a very short radiative lifetime of 1.2 nanoseconds, in very good accord with experiments.