Thickness-dependent properties of color centers in hexagonal boron nitride: a first principles study

Since the discovery of quantum emission from hexagonal boron nitride (hBN) in 2016, a significant research effort has been directed to determine the chemical identities of the color centers responsible for the observed quantum emission. In the process, works have shown that properties of the as-yet unidentified color centers, such as their photo-stability and luminosity, are affected by: (i) the number of hBN layers, (ii) the presence of a substrate and (iii) even the twist angle between the layers. In addition, experiments show a wide spread in emission frequencies of the color centers. However, the mechanisms that result in the observed changes in properties have not been identified, although there is some indication that the strain in the hBN layers may be playing a role [Phys. Rev. Research 2, 022050(R) (2020)]. In this work, we used density functional theory to explore whether the presence of multiple layers is a source of strain due to “interlayer-friction”. We also determine the size of the thickness-dependent changes in excited state properties, and show how it contributes towards the spreads in quantum emission frequencies that have been observed in experiment.