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.
Keywords: 2D materials; color centers; nanophotonic effects; quantum sensing.