  Tellurium impurity centers in ZnSe were individually probed with
time-resolved photoluminescence (PL) spectroscopy. Resolution-limited peaks
with an ultra-low spatial density originate in the recombination of excitons
deeply bound to isolated nearest-neighbor isoelectronic Te pairs (Te2). This
interpretation is confirmed by ab-initio calculations. The peaks reveal
anti-bunched photon emission and a doublet structure polarized along [110] and
[-110]. We analyze the time-resolved PL decay to clarify the role of the dark
states in the spin relaxation and radiative recombination of single
fine-structure split excitons.
