Time-Resolved Spectroscopy of Single Excitons Bound to Pairs of Te Isoelectronic Impurity Centers in ZnSe

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.