Abstract
Among a broad diversity of color centers hosted in layered van der Waals materials, the negatively charged boron vacancy (VB–) center in hexagonal boron nitride (hBN) is garnering considerable attention for the development of quantum sensing units on a two-dimensional platform. In this work, we investigate how the optical response of an ensemble of VB– centers evolves with the hBN thickness in a range of a few to hundreds of nanometers. We show that the photoluminescence intensity features a nontrivial evolution with thickness, which is quantitatively reproduced by numerical calculations taking into account thickness-dependent variations of the absorption, radiative lifetime, and radiation pattern of VB– centers. Besides providing an important resource to optimize the performances of quantum sensing units based on VB– centers in hBN, the thickness-dependent nanophotonic effects discussed in this work generally apply to any type of color center embedded in a van der Waals material.