  We have synthesized CdS(1.3 nm)/CdSe(1.7 nm)/CdS(3.4 nm) spherical quantum
wells with 13 nm diameter and demonstrated the first antibunching of their
emission, labelling them as single-photon sources. Antibunching survives even
at high excitation intensities, ruling-out bi-exciton emission. For the largest
intensities, antibunching coupled to spectral measurements, reveal the
signature of a blue-shifted emission, associated to an irreversible photo-aging
effect. We demonstrate a moderate correlation between the main and the
blue-shifted emission energy. Intensity-timetraces show low-blinking, with a
median time spent in the bright state of 89 %. Emission lifetime measurements
reveal a complex emission dynamic with either three or four components. While
spherical quantum wells have been initially designed for laser-oriented
applications, we demonstrate that they can serve as single-photon sources.
