Impact of Thickness-Dependent Nanophotonic Effects on the Optical Response of Color Centers in Hexagonal Boron Nitride.

Among a broad diversity of color centers hosted in layered van der Waals materials, the negatively charged boron vacancy (V _B ^- ) 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 V _B ^- 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 V _B ^- centers. Besides providing an important resource to optimize the performances of quantum sensing units based on V _B ^- 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.