title: Energy Gap Tuning and Carrier Dynamics in Colloidal Ge1-xSnx Quantum Dots.
abstract: Optical transition energies and carrier dynamics in colloidally synthesized 2.0 ± 0.8 nm Ge1-xSnx quantum dots (x = 0.055-0.236) having visible luminescence were investigated using steady-state and time-resolved photoluminescence (PL) spectroscopy supported by first-principles calculations. By changing Sn content from x = 0.055 to 0.236, experimentally determined HOMO-LUMO gap at 15 K was tuned from 1.88 to 1.61 eV. Considering the size and compositional variations, these values were consistent with theoretically calculated ones. At 15 K, time-resolved PL revealed slow decay of luminescence (3-27 μs), likely due to the recombination of spin-forbidden dark excitons and recombination of carriers trapped at surface states. Increasing Sn concentration to 23.6% led to 1 order of magnitude faster recombination. At 295 K, PL decays were 3 orders of magnitude faster (9-28 ns) owing to the thermal activation of bright excitons and carrier detrapping from surface states.
authors: Department of Electrical and Computer Engineering, Virginia Commonwealth University , Richmond, Virginia 23284, United States.
authors: Shopan A
authors: SA
authors: Hafiz
authors: Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284, United States.
authors: Richard J Alan
authors: RJ
authors: Esteves
authors: Department of Physics, Virginia Commonwealth University , Richmond, Virginia 23284, United States.
authors: Denis O
authors: DO
authors: Demchenko
authors: Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284, United States.
authors: Indika U
authors: IU
authors: Arachchige
authors: Department of Electrical and Computer Engineering, Virginia Commonwealth University , Richmond, Virginia 23284, United States.
authors: Ümit
authors: Ü
authors: Özgür