Negatively charged boron-vacancy defect in hexagonal boron nitride nanoparticles

Fluorescent defects in two-dimensional (2D) hexagonal boron nitride (hBN) crystals have attracted a great potential in quantum information and sensing technologies. In particular, the negatively charged boron vacancy (VB−) center has shown spin-dependent fluorescence in 2D flakes or large hBN crystals, which can be manipulated at room temperature, enhancing the application scope of hBN in quantum technologies. In this work, we demonstrate the generation of this interesting spin defect in small hBN nanoparticles (NPs) with a size range of 10–50 nm. The obtained optical properties of the VB− showed a photostable photoluminescence peaked at 820 nm with a spin-lattice relaxation time (T1) of 17 μs and optically detected magneto resonance (ODMR) contrast of 10%. Achieving long T1 time and high ODMR contrast is crucial for effective quantum sensing using small hBN nanocrystals. The reported spin-optical properties of the generated VB− spin defect in hBN NPs are comparable to those created in bulk/flake hBN crystals. These results open the door for optimizing such spin-dependent defects in small hBN NPs for promising applications, especially in quantum sensing and biology.