Fig. 1. NDs containing GeV color centers. (a) AFM image showing the typical size of the NDs. The numbered white circles refer to the corresponding height profiles. (b) Characteristic PL spectrum of a typical ND containing GeV color center(s) with ZPL at 602 nm. Inset: second-order autocorrelation function indicating emission from a single GeV, g(2)(0)=0.37±0.02. The purple shading in the spectrum indicates the band of wavelengths selected by the bandpass filter in the autocorrelation measurement.

Fig. 2. BFP analysis of three individual GeV single-photon emitters. (a) BFP images measured experimentally for each individual emitter. (b) Corresponding simulated 2-D dipole fits. The fitted in-plane (ϕ) and out-of-plane (θ) angles of the crossed dipole (subscripts 1 and 2) for each GeV center are indicated explicitly.

Fig. 3. Summary of the optical properties of characteristic NDs containing GeV centers. (a) Kinetic spectra measurement of a single GeV emitter, showing photostable emission at 604 nm (FWHM ~ 4.27 nm) for 500 s at 10-s integration time intervals. (b) Saturation measurement of the emitter. The extracted saturation intensity is I∞=7.14×105counts/s. (c) Histogram of the emitter lifetime. (d) Histogram of emitter ZPL position. (e) Histogram of FWHMs of the fitted ZPLs. The dotted lines represent the average values of their respective dataset. Each histogram represents a sample size of 18 individual emitters.

Fig. 4. Measured QE of GeV ensembles. (a) Schematic illustration of the sample: in the first step of the experiment (cf. main text) the NDs lie on a transparent coverslip in air; in the second step of the experiment they are covered with a 1.5-μm thick layer of PMMA acting as an unbound dielectric medium. (b) Filtered emission lifetime measurements before (purple trace) and after (orange trace) deposition of ∼1.5μm of PMMA. (c) Simulated values for the ratio between radiative rates as a function of PMMA thickness for parallel (orange trace) and perpendicular (purple trace) dipole orientations. Inset figure shows the simulated values for the range 0 to 200 nm.