Fig. 3: Bleaching mechanism of P3 emission in monolayer CVD hBN.
From: Prolonged photostability in hexagonal boron nitride quantum emitters
a Schematic of a custom-built environmental chamber with a quartz observation window, which could be filled with different gases. b Time-trace of P3 emission in monolayer CVD hBN under a N2 atmosphere. c Initial 10 s of overall decay curves of P3 emission in monolayer CVD hBN under N2 (blue line), N2 with saturated water vapor (green line), air (yellow line) and O2 (red line). The number of time-traces (N) included in each decay curve is 8 (blue, N2), 20 (green, N2 with saturated water vapor), 31 (yellow, air) and 36 (red, O2), respectively. d Intensity decay curve (blue line) of monolayer CVD hBN under N2 (N = 8) is fitted with a single exponential decay function (red dashed line) and two exponential decay functions (yellow dashed line), where the single-decay-fit shows larger discrepancy. From the two-exponential fit with 95% confidence interval, we obtain two bleaching lifetimes of \({\tau }_{1}\) = 5.0 ± 1.1 s and \({\tau }_{2}\) = 150 ± 10 s. e Schematic of laser power dependence measurement, with monolayer CVD hBN on SiO2 substrate in the air. f Illustration of a three-energy-system with ground singlet state (G), excited singlet state (S) and excited triplet state (T). Photobleaching reactions could occur from both excited states, with microscopic rate constants of kbS and kbT. Rate constants of ke, kf and kIC correspond to excitation, fluorescent emission and internal conversion, respectively. Additionally, kISC and kT correspond to intersystem crossing and depopulation from T to G, respectively. g Beaching rate 1/\(\tau\), i.e., the inverse of bleaching lifetime, is linearly dependent on the power density of the incident laser, which could be well explained by the three-energy-system in (f). For the three data points in the lower power density range, each is extracted from the sum of ~100 time-traces; and for the other three, each is extracted from the sum of 20 to 30 time-traces. The error bars correspond to 95% confidence intervals. h Four-layer stack (right) is constructed by repeatedly transferring monolayer CVD hBN onto the same substrate. i Total intensity of four-layer stack (green line) in the air (N = 27) is fitted with a single exponential decay function (red dashed line) and two exponential decay functions (yellow dashed line), where the latter is a better fit. The two bleaching lifetimes are 11 ± 3.9 s and 150 ± 20 s, respectively.
