Identifying the Origin of Hexagonal Boron Nitride Single Photon Emitters with nano-FTIR.

Quantum light sources in van der Waals solid systems operating at room temperature have drawn significant attention, among which, with particular interest, is hexagonal boron nitride (hBN). Numerous efforts have focused on producing reliable, bright, and controllable single photon emitters (SPEs) in hBN. However, the identity of these emitters remains ambiguous, leading to unreproducible experimental results. Here, we offer direct evidence that hBN SPEs generated through annealing are not inside the hBN itself but originate from organic residues that carbonize and form aromatic fluorophores. Nanoscale Fourier transform infrared spectroscopy is used to analyze the emission sites, revealing the presence of carbon bonds in aromatic rings with a characteristic C═C absorption peak at 1650 cm-1. These emitters are primarily located in encapsulated areas of the hBN flake rather than uniformly distributed within the lattice. This finding opens the door to designing stable and reliable SPEs, enabling their integration into the rapidly growing quantum photonics applications.