Abstract
We report spectroscopic characterization of Fe:ZnSe quantum dots (for 2% of Zn/Fe molar ratio) fabricated by microemulsion hydrothermal synthesis. Mid-IR photoluminescence of the 5E↔5T2 transition of Fe2+ ions over 3.5-4.5 μm spectral range was observed in Fe:ZnSe quantum dot samples and kinetics of luminescence have been characterized at temperatures of 30-300 K under direct (2.788 μm) mid-IR excitation and indirect (0.355 μm) photoionization excitation. The radiative lifetime (τrad) was estimated from these measurements to be 48 µs while lifetime at room temperature was measured to be 440 ns. This agrees closely with the behavior of bulk material.
Highlights
Transition metal (TM) doped and undoped wideband II–VI semiconductor nanoparticles and quantum dots (QDs) have attracted a great deal of interest
Works studying II–VI QDs doped with transition metals prepared by chemical means have demonstrated poor optical characteristics in the mid-IR spectral region due to the high density of surface defects associated with most methods of synthesis resulting in the quenching of mid-IR luminescence [14,15,16]
Mid-IR luminescence in the 2–6 μm spectral range has been demonstrated in Co, Cr, and Fe doped II–VI nanocrystals produced by laser ablation, and laser oscillation has been achieved under direct excitation [12,17]; this laser ablation method is not readily scalable and offers poor control of particle size distribution
Summary
Transition metal (TM) doped and undoped wideband II–VI semiconductor nanoparticles and quantum dots (QDs) have attracted a great deal of interest. In the case of ZnSe, crystals doped with TMs (such as Mn and Cu) have been characterized extensively and successfully with the stable and efficient band–edge emission at energies slightly lower than the band-gap (580 to 600 nm for Mn:ZnSe [4,5,6], 350 to 500 nm for Cu:ZnSe [7,8,9]) These TM doped QDs exhibit high efficiency and high temperature stability as well as long photoluminescence lifetimes. Works studying II–VI QDs doped with transition metals (such as Ni, Co, Fe, and Cr) prepared by chemical means have demonstrated poor optical characteristics in the mid-IR spectral region due to the high density of surface defects associated with most methods of synthesis resulting in the quenching of mid-IR luminescence [14,15,16]. We demonstrate the first spectroscopic characterization of chemically synthesized Fe:ZnSe QDs in the mid-IR spectral range over a range of temperatures (30– 300K)
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