Fig. 4

The density evolution of emitters on pre-annealing only (B1), pre-annealing followed by irradiation (B2), pre-annealing followed by post-annealing in nitrogen in graphite box (B3), pre-annealing followed by irradiation and post-annealing (B4). The blue circles are the results from Type I hBN flakes, and the black squares are those from Type II hBN flakes.