Fig. 5: Single-photon emission from a 30-nm CsPbBr₃ QD.

a, Single-QD photoluminescence spectrum with (red) and without (black) a tunable long-pass filter rejecting biexciton emission. In the unfiltered spectrum, for each the exciton (X) and biexciton (XX), three sublevels are well resolved, denoted as V, H and O, respectively, with an average fine-structure splitting of 1.06 meV. b, Polarization-resolved photoluminescence spectra of biexciton and exciton, respectively. c, Intensity of the biexciton (left) and exciton sublevels (right) as a function of polarization angle, extracted by performing three-Lorentzian fitting on the spectra in b. The grey lines show a sin² fit to the respective linearly polarized dipoles in the observation plane. A low signal-to-noise ratio for the XX-O state precludes a precise assignment of its polarization characteristics. d, Second-order intensity correlation g⁽²⁾(τ) acquired without spectral filtering. e, Second-order intensity correlation g⁽²⁾(τ) acquired after filtering out biexciton emission. A strong anti-bunching g⁽²⁾(0) < 0.5 is observed, attesting to single-photon emission from exciton recombination.