Kinetics of excitation transfer from Cr2+ to Fe2+ ions in co-doped ZnSe

The transfer of electronic excitations from Cr2+ to Fe2+ ions in co-doped epitaxially grown ZnSe is studied by time-resolved photoluminescence (PL) spectroscopy with unprecedented sub-10 ns time resolution. Upon excitation of Cr2+ ions by a picosecond pulse at 2.05 mu m wavelength, PL from Fe2+ ions displays a delayed onset and a retarded decay in comparison to Fe2+ PL directly excited at 3.24 pm. We measure an extremely rapid 60 ns buildup of the Fe2+ luminescence, which is followed by a slower relaxation on the few micrometer scale. The experimental results are analyzed in the framework of Forster radiationless resonant energy transfer. Directly connecting to the work of Fedorov et al. [Opt. Mater. Express 9, 2340 (2019)1, the 60-ns buildup time of energy transfer is found to correspond to a Cr2+-Fe2+ distance of 0.95 nm, close to the length of the space diagonal of the ZnSe unit cell. This result demonstrates a significant density of spatially correlated Cr2+-Fe2+ ion pairs at short distance, in parallel to ions with a random distribution at a larger mutual separation. (C) 2022 Optics Publishing Group

Automated summary

The transfer of electronic excitations from Cr2+ to Fe2+ ions in co-doped epitaxially grown ZnSe was studied by time-resolved photoluminescence spectroscopy, revealing a rapid 60 ns energy transfer buildup and a 0.95 nm Cr2+-Fe2+ distance.